There is human and animal evidence that BPA exposure, at low levels, could contribute to the development of insulin resistance, glucose intolerance, and type 2 diabetes. BPA may also be able to affect body weight, although studies are somewhat inconsistent. In fact, an expert panel of scientists has estimated that prenatal BPA exposure has a 20 - 69% probability of causing 42,400 cases of childhood obesity in the European Union, with associated lifetime costs of €1.54 billion (Legler et al. 2015).
BPA has not been evaluated in relation to type 1 diabetes in humans, but can affect beta cells, promote autoimmunity, and affect diabetes development in a mouse model of type 1 diabetes-- all of which may be important for type 1 diabetes.
The strongest evidence for the ability for environmental exposures to contribute to the development of diabetes comes from longitudinal studies. These are studies that take place over a period of time, where the exposure is measured before the disease develops.
The first published longitudinal study of BPA and type 2 diabetes used data from the U.S. Nurses Health Studies 1 and 2. In the Nurses Health Study 1, which includes older women (average age 66), BPA levels were not associated with type 2 diabetes. However, in the Nurses Health Study 2, which includes middle-aged women (average age 46), BPA levels were associated with type 2 diabetes (after adjusting for body mass index (BMI)). Thus, BPA exposures may be associated with the risk of type 2 diabetes among middle-aged women, but not older women. These findings may be due to menopausal status (although chance cannot be ruled out). While the younger women had higher levels of BPA than the older women, these differences did not explain the findings. Because experimental data suggests that BPA interferes with the function of the insulin-producing pancreatic beta cells by activating estrogen receptors, the authors hypothesized that any associations between BPA and diabetes would be stronger in pre-menopausal women than post-menopausal women. Indeed, the association between BPA and diabetes shows a clear linear trend in pre-menopausal women, but there is no association in post-menopausal women. And, the association between BPA and diabetes was stronger in women who developed diabetes at a younger age (under 55). These interesting findings should be examined in other cohorts. Note that this paper also found similar results for phthalate exposure levels (Sun et al. 2014).
A similar study by many of the same authors, also based on the Nurses Health Studies, found that women (without diabetes) with the highest levels of BPA (and some phthalate) exposure gained more weight during the 10 year follow-up period than those with lower levels of exposure (Song et al. 2014). For an article describing this study, see Household chemicals linked to slight weight gain, published by Environmental Health News.
A study of middle-aged and elderly East Asians found that BPA levels were associated with fasting glucose levels only in people with genetic risk of diabetes (Bi et al. 2015).
A study of adults over age 40 in Shanghai, China, found that BPA levels were associated with a higher risk of developing obesity, over a 4 year period, especially in women, individuals who were younger than 60, those of normal weight, non-smokers, non-drinkers, and those without high blood pressure (Hao et al. 2017).
A study of elderly adults from Sweden did not find any associations between BPA levels and measures of obesity (fat mass and fat distribution) two years later. It did, however, find associations between BPA levels and the hormones adiponectin, leptin, and ghrelin, implying that BPA may interfere with the hormonal control of hunger and satiety (Rönn et al. 2014). Yet a different longitudinal study of the elderly in South Korea found BPA levels were associated with overweight in women, but not men (Lee et al. 2015).
A Belgian study of adults found that those who were obese had higher levels of BPA than those who were not. Over 3, 6, and 12 months of weight loss (via either dieting or bariatric surgery), levels of BPA did not change (Geens et al. 2015).
Evidence is growing that exposure to pollution during critical developmental periods, such as in utero or during childhood, may have effects later in life.
Most of the longitudinal human studies on BPA thus far are related to growth and body weight outcomes (not diabetes), all at typical U.S. exposure levels.
A Dutch study found that infants born to women with higher amounts of BPA had smaller heads and grew slower in the womb than infants whose mothers had lower amounts of BPA. The results were more significant depending on how often the BPA was measured during the pregnancy; the more measurements, the more significant (many other BPA studies rely on one measurement of BPA, which is less accurate-- this study measured BPA multiple times). The study suggests that BPA exposure during pregnancy may impair fetal growth (Snijder et al. 2013). For an article describing this study, see BPA is associated with slower growth before birth, published by Environmental Health News. A study from University of Michigan hospitals found that BPA exposure was associated with lower birth weight and taller height (Veiga-Lopez et al. 2015). (Note that lower birth weight is associated with an increased risk of type 2 diabetes as well as other outcomes).
A Spanish study found that prenatal BPA levels were associated with increased waist circumference and higher body mass index (BMI) at age 4, but not at earlier ages (Valvi et al. 2013). The same study, when including 27 different endocrine disrupting chemicals, found that in utero levels of various persistent organic pollutants were associated with overweight/higher BMI at age 7, while other chemical levels (BPA, arsenic, phthalates, flame retardants, lead, and cadmium) were not associated (Agay-Shay et al. 2015).
Prenatal BPA exposures were associated with a lower BMI, less body fat, and less overweight/obesity in Californian girls at age 9, while current BPA levels were associated with higher BMI, obesity/overweight, waist circumference, and fat mass at that age (Harley et al. 2013). For an article describing this study, see Unclear relationship: Prenatal but not concurrent bisphenol A exposure linked to lower weight and less fat, published by Environmental Health Perspectives (Betts 2013).
A U.S. study from Cincinnati found that prenatal BPA exposure levels were not associated with BMI in early childhood. Children with the highest exposures, however, grew fastest between age 2 and 5 (Braun et al. 2014).
A Canadian study found that first-trimester maternal levels of BPA were associated with adipnectin levels in male infants-- a hormone that controls a number of metabolic processes, such as blood glucose. These infants will be followed to see if there are any later-life effects (Ashley-Martin et al. 2014).
A study from Crete (Greece) found that while prenatal BPA levels were not consistently associated with excess weight, exposure levels in early childhood were. BPA exposure levels at age 4 were associated with a higher BMI, waist circumference and skinfold thickness (Vafeiadi et al. 2016).
A study from New York City found that prenatal BPA levels were not associated with fat mass during childhood (age 4-9) (Buckley et al. 2016). However another New York City study of a different group of people found that prenatal BPA levels were associated with fat mass during childhood, as well as percent body fat and waist circumference at age 7 (BPA levels during childhood were not associated with any of these outcomes) (Hoepner et al. 2016).
BPA exposure levels in pre-adolescent girls were associated with higher insulin and insulin resistance levels one year later, in a study from Korea (Lee et al. 2013). Another Korean study found that maternal BPA levels were associated with higher diastolic blood pressure in children at age 4 (Bae et al. 2016).
Thus the results vary by study, with some showing that BPA may increase the risk of obesity, and others showing that BPA may decrease the risk of obesity. In either case, BPA may be able to affect growth rates, and the details and effects remain to be determined-- these effects may depend on a variety of things, such as the population studied, other environmental exposures, timing of exposure, dose of exposure, socio-economic factors, nutrition, etc. Also, many of the animal studies that find that BPA exposure leads to a higher body weight (see below) do not find that increase in body weight until the exposed animals reach puberty (Betts 2013).
Cross-sectional studies are studies that measure exposure and disease at one point in time. These provide weaker evidence than longitudinal studies, since the disease may potentially affect the exposure, and not vice versa.
A number of cross-sectional human studies on BPA use the same dataset, the National Health and Nutrition Examination Survey (NHANES), which is the Center for Disease Control and Prevention’s biennial biomonitoring survey of a large sample of U.S. residents. Using NHANES data from 2003/04, Lang et al. (2008) found that higher BPA concentrations in urine were associated with diabetes and cardiovascular diagnoses, but not with other common diseases. Melzer et al. (2010) then analyzed NHANES data from a subsequent survey, from 2005/06, and found that in those years, BPA levels were lower than they had been in 2003/04. The association between heart disease and BPA remained significant in 2005/06. The association between BPA and diabetes was significant in pooled data (2003-06), but did not reach significance in 2005/06 alone.
Shankar and Teppala (2011) also analyzed NHANES data, and found that pooled data from 2003-08 show a positive association between BPA and diabetes. Silver et al. (2011) took a slightly different view of the 2003-08 NHANES data, defining diabetes by whether or not participants took a diabetes medication, or had high long-term blood glucose levels (instead of using self-reported diabetes, as in the previous analyses). These authors also found an overall positive association between BPA and diabetes in 2003-08 pooled data, although breaking down by year, the association was only significant in 2003/04, not 2005/06 or 2007/08. Curiously, average BPA levels in 2007/08 were up again slightly, after falling between 2003/04 and 2005/06.
Also using NHANES data, Beydoun et al. (2014) found that higher BPA levels were associated with higher insulin levels and increased beta cell function, as well as increased insulin resistance, especially in males.
In adults, BPA was associated with a higher BMI and waist circumference in both genders and in all ethnic groups (also NHANES data, from 2003-2008) (Shankar et al. 2012). Another study, based on NHANES data (from 2003-2008), found that BPA levels were associated with metabolic syndrome in adults (Teppala et al. 2012). Metabolic syndrome is a cluster of conditions associated with type 2 diabetes, sometimes preceding the disease. Some of the same authors also found (using the same data), that BPA was associated with pre-diabetes, defined as a somewhat high fasting blood glucose level or post-meal blood glucose level (not to the point of diabetes) (Sabanayagam et al. 2013). Another study, using NHANES data from 2003-2006, found that among adults, BPA levels were associated with both general obesity and central obesity (Carwile and Michels, 2011).
A Canadian study using a similarly designed dataset (the Canadian Health Measures Survey, a survey of the general population), found that BPA levels were associated with diabetes, glucose levels, and HbA1c levels (a measure of long-term blood glucose control) in adult men (but not women) (Tai and Chen 2016).
Another study on BPA and diabetes analyzed a group of Chinese adults, whose average urinary BPA level was lower than in the US. Dividing participants into quartiles of BPA exposure, the data shows that risk of diabetes was higher in people in the second and fourth quartiles of exposure, but not the third. The overall trend was not significant (Ning et al. 2011). However, since BPA is an endocrine disruptor, a linear association would not necessarily be expected.
A study has found an association between BPA levels and increased insulin resistance, general obesity, and abdominal obesity in Chinese adults over 40 living in Shanghai (Wang T et al. 2012).
A study from Korea found that while the risk of diabetes was somewhat higher in adults with the highest levels of BPA, the results were not statistically significant (Kim and Park, 2013). In contrast, a study from Iran found that the risk of diabetes was much higher in adults with the highest levels of BPA (Ahmadkhaniha et al. 2014). Another study of Koran adults found that those with higher BPA levels had a higher waist circumference and were more likely to be obese than those with lower levels. BPA levels were associated with BMI and body fat as well (Ko et al. 2014).
In a study from Thailand, BPA levels were highest in adults with diabetes than in those without diabetes, with a stronger association in men than women. Impaired fasting glucose levels were not associated with BPA (Aekplakorn et al. 2014).
A study of Italian adults found that BPA levels were associated with higher waist circumference, triglycerides, inflammation, glucose levels, and visceral adiposity (Savastano et al. 2015). A Korean study also found associations between BPA and markers of inflammation, regardless of obesity or insulin resistance (Choi et al. 2016).
A small pilot study from Cyprus found that while total BPA levels were not associated with diabetes, monochlorinated BPA levels were strongly associated with diabetes. Monochlorinated BPA is formed when chlorine-containing chemicals come in contact with BPA (Andra et al. 2015). Expanding their analysis to a larger group, and this time looking at obesity, these same authors found that an association between BMI and monochlorinated BPA that was relatively weak (Andra and Makris 2015).
The cross-sectional studies of children and BPA thus far are related to growth and body weight outcomes (not diabetes).
A study published in the prestigious Journal of the American Medical Association, also based on NHANES data (from 2003-2008), found that Caucasian children (not Blacks or Hispanics) with higher levels of BPA had higher rates of obesity (Trasande et al. 2012). Another study of children using NHANES data (also from 2003-2008) similarly found that those with higher levels of BPA were more likely to be obese, especially non-Hispanic whites (Bhandari et al. 2013). And, a study using NHANES data from 2003-2010 found that BPA was associated with a higher risk of obesity as well as an abnormal waist circumference-to-height ratio in children. The study did not find associations between BPA and insulin or glucose levels (Eng et al. 2013). The children in all of these studies were ages 6-18. Another study using NHANES data (from 2003-2006, in children 8-19), found that BPA levels were associated with higher lean body mass index in boys, and higher fat mass in girls (Li et al. 2017).
A Canadian study found no association between BPA levels and diabetes or blood glucose levels in children (but as mentioned above, there was an association in adult men) (Tai and Chen 2016).
Higher BPA levels have been linked to higher body mass index (BMI) in Chinese schoolchildren in Shanghai, aged 8-15 (Wang HX et al. 2012). Another study of Shanghai schoolchildren found that girls aged 9-12 with the highest BPA levels (equivalent to average levels in the U.S.) had twice the risk of excess body weight (over 90th percentile) as those with the lowest exposure levels (Li et al. 2013). In Italian children, BPA levels were associated with BMI as well (D'Aniello et al. 2014). However, in children from India, BPA was not associated with obesity (Xue et al. 2014).
A study of U.S. children (using NHANES data from 2003-2010) found that BPA levels were associated with an increased weight-to-height ratio (WHR), a measure of central obesity. WHR is thought to be a better indicator of cardiovascular risk than BMI (Wells et al. 2014).
A small study of overweight or obese Ohio children aged 3-8 found that BPA levels were associated with higher insulin resistance and other metabolic differences (Khalil et al. 2014). A study of obese Italian children found that BPA levels were directly associated with inulin resistance, no matter the BMI. In addition, laboratory experiments showed that BPA does indeed have these effects on children's fat cells (Menale et al. 2016).
Laboratory studies are often used to determine the mechanisms through which environmental chemicals act.
A single injection of BPA increases insulin levels and decreases blood glucose levels in adult mice. Over a 4 day exposure period, BPA increased insulin levels and insulin resistance in mice, and decreased glucose tolerance-- at doses well below the supposed "safe" level designated by the U.S. EPA (Ropero et al. 2008; Alonso-Magdalena et al. 2006). After an 8 day exposure, adult mice developed insulin resistance and showed disrupted insulin signaling in numerous body tissues (Batista et al. 2012). You might ask how a chemical found to lower blood glucose levels in mice is suspected to contribute to the development of diabetes-- a disease defined by high blood sugar levels-- and that would be a good question. The scientists who conducted this research point out that excess insulin in the blood can itself cause insulin resistance as well as beta cell dysfunction, eventually leading to type 2 diabetes (Nadal et al. 2009). In addition, while the immediate effects of one injection was a lowering of blood glucose, the chronic effects of BPA exposure over a few days time -- including the decrease in glucose tolerance -- caused BPA-exposed mice to have higher blood glucose levels than the unexposed mice after a glucose tolerance test (Alonso-Magdalena et al. 2006). You might just say that these studies show that BPA can mess with blood glucose and insulin levels. And, mice exposed to low levels of BPA for a longer time period-- 8 months-- developed high blood sugar as well as high cholesterol levels (Marmugi et al. 2014). Other authors found that after just 4 weeks of BPA exposure, mice developed high blood sugar (and higher body weight) as well (Moghaddam et al. 2015).
There also may be interactions with diet. Mice exposed to low doses of BPA for 30 days showed increased body weight and fat mass when fed a normal diet, but not a high-fat diet (Yang et al. 2016).
Rabbits exposed to BPA developed insulin resistance, fatty liver, hardening of the arteries, and heart problems (Fang et al. 2015).
BPA is considered an environmental estrogen, because it can act similarly to the hormone estrogen. The mechanism whereby BPA promoted insulin secretion has been shown to involve estrogen receptors (Adachi et al. 2005; Soriano et al. 2012). BPA can promote insulin secretion and also insulin resistance via its estrogenic effects (Alonso-Magdalena et al. 2006).
BPA may have other effects related to diabetes as well. Adult male mice exposed to the supposed "safe" dose of BPA for 2 weeks had impaired glucose sensing in their liver. Glucose sensing is important because it is the way the body tells what the blood sugar level is, and how to react. Glucose sensing is impaired in people with type 2 diabetes, and we don't know why (Perreault et al. 2013).
BPA even affects fruit flies. These effects, involving the gut as well as metabolism-related tissues, involved epigenetic mechanisms, and were enhanced with a high-sugar diet (Branco and Lemos, 2014).
Most of the animal research on BPA has involved exposing pregnant animals to the chemical, then looking for effects on the offspring.
One of the first studies on this topic found that when pregnant mice were exposed to low and high doses of BPA, the exposed male offspring, at 6 months of age, had increased insulin resistance, reduced glucose tolerance, and altered insulin secretion. The offspring exposed to the lower doses of BPA in utero had higher birth weights than the controls, while the offspring exposed to the higher doses in utero had lower birth weights. The results suggest that BPA could contribute to the development of diabetes, and predispose male offspring to type 2 diabetes in adulthood (Alonso-Magdalena et al. 2010). The researchers at this laboratory have also treated mice with BPA during pregnancy, and then fed the offspring either a normal or high-fat diet (controls in both diet groups were not exposed to BPA). The BPA group fed a normal diet caught up in weight to the unexposed high-fat diet before age 28 weeks. Both BPA-exposed groups and the high-fat diet group developed high fasting blood sugar, glucose intolerance, disrupted insulin release from beta cells, high triglycerides, and other effects as well, all of which resemble type 2 diabetes and obesity in humans (García-Arevalo et al. 2014).
A number of other researchers have pursued this topic further. When researchers exposed mother rats to BPA during pregnancy and lactation, their offspring weighed more and had glucose intolerance as adults. If the offspring were fed a high-fat diet, these effects were accelerated and exacerbated: they were obese and developed severe metabolic syndrome. Interestingly, these effects showed up at the lowest dose of BPA, but not the higher doses (Wei et al. 2011). Male offspring rats exposed to BPA while in the womb and through lactation had higher blood glucose levels and insulin resistance. These effects showed up earlier in life in the rats that received a higher dose, and later in life in the lower dosed rats (Song et al. 2014).
In another study, pregnant and lactating mice were exposed to high and low doses of BPA (both relevant for human exposure). The male offspring exposed to the higher BPA dose developed glucose intolerance as adults. The female offspring exposed to the higher BPA dose were heavier, ate more, and had more fat than the unexposed offspring, although only when they ate a high-fat diet as adults (Mackay et al. 2013). According to the English abstract of a study published in Chinese, researchers found that the offspring of BPA-exposed pregnant and lactating rats had higher fasting blood glucose levels and insulin levels, as well as higher body weight at birth and after weaning (Liu et al. 2012).
Rat offspring whose mothers were exposed to BPA during pregnancy and lactation developed impaired glucose tolerance (only males), and higher glucose-stimulated insulin secretion (Galyon et al. 2016). Another rat study found that develomental exposure to BPA resulted in significantly increased body weight and adipose tissue, abnormal serum lipids, and lower adiponectin levels in both female and male offspring (Gao et al. 2016).
Rats exposed to BPA during development showed higher body weight throughout life, an effect that was somewhat lessened in the animals fed a soy-based diet (Patisaul et al. 2014). Other studies have also found that rats exposed to low doses of BPA during development show a variety of metabolic disruption effects, including changed glucose metabolism (Tremblay-Franco et al. 2015) and increased body weight later in life (in females) (Hass et al. 2016). However, other studies have found that BPA exposure during development can also lead to lower body weight and food intake later in life (Suglia et al. 2016).
Miyawaki et al. et al. (2007) found that mice exposed to BPA in the womb and afterwards developed obesity as well as lipid abnormalities. Rubin et al. (2001) found that mother rats exposed to low doses of BPA had heavier offspring, even after the exposure ended. The weight gain persisted longer in females, and, interestingly, was higher at lower doses. Exposure to BPA in utero and in early life can not only affect the body weight of animals, but affect fat cells as well (Rubin and Soto 2009).
Juvenile male mice exposed to BPA for 12 weeks developed glucose intolerance and insulin resistance, in combination with a high fat diet. The BPA made the problems worse than the diet alone (Moon et al. 2015). Rats exposed to BPA only while in the womb showed lower levels of adiponectin and other hormones, and higher levels of leptin and insulin as fetuses (Ahmed 2016). Developmental exposure to BPA also affected leptin sensitivity in mice offspring in adulthood (MacKay et al. 2017).
Sheep have also been exposed to BPA during pregnancy, and their offspring also show metabolic changes that can lead to insulin resistance, although the outcomes depended on the genetic strain of sheep (Veiga-Lopez et al. 2105). Curiously, these authors also found that BPA exposure prevented the adverse effects of postnatal obesity in inducing high blood pressure. BPA also partially reversed the effects of overfeeding. Note that BPA did, however, affect many genes related to obesity, blood pressure, and heart disease (Koneva et al. 2017). Cow embryos exposed to low levels of BPA showed metabolic effects, even as embryos (Choi et al. 2016).
An extensive study designed to test how BPA can program metabolism in early life -- at levels relevant to human exposures -- exposed mice during gestation and lactation to 8 different low doses of BPA, and followed offspring for 20 weeks after weaning, with no further exposure (until mouse adulthood). The effects varied depending on sex: adult male offspring showed dose-dependent increases of body and liver weights, no effects on fat pad weights and a dose-dependent decrease in glucagon levels. Adult female offspring showed a dose-dependent decrease in body weight, liver, muscle and fat pad weights, fat cell size, lipids (fats, e.g., cholesterol levels), leptin and adiponectin levels. Physical activity was decreased in exposed males and slightly increased in exposed females. These results suggest that BPA cannot be categorically labeled an obesogen-- males showed higher body weight from exposure while females showed lower-- but that BPA does have the ability to alter metabolism later in life, following early life exposure, and that the specific effects vary by sex (van Esterik et al. 2014). The mechanisms did not appear to involve DNA methylation, an epigenetic change (van Esterik et al. 2014b).
BPA affects the development of the pancreas
When pregnant mice were exposed to BPA, their fetuses showed altered pancreatic development. These changes may have implications for both the structure and function of the pancreas in later life (Whitehead et al. 2016).
Another study also showed that when pregnant mice were exposed to BPA, it affected the development of the pancreas. For the first month of life, the exposed animals had higher beta cell mass, but at 4 months, beta cell mass was equal or lower than the unexposed controls. The exposed mice also had altered fasting glucose levels (García-Arévalo et al. 2016).
In fact, some authors point out that developmental exposure to BPA affects not only the pancreas but also the other organs that also derive from the endoderm, including the thyroid, liver, gut, prostate and lung (Porreca et al. 2016).
Another phenol, 4-tert-octylphenol, when given during development, has adverse effects on fat metabolism in pregnant rats (Kim et al. 2015).
Some researchers have tried to determine the "critical windows of exposure" for BPA in relation to how it can cause glucose intolerance in animals. That is, when is an animal most susceptible to the glucose intolerance effects of BPA? These scientists exposed pregnant and lactating mice to different amounts of BPA at different times during and/or after pregnancy, and studied the effects on the offspring, later in life. Overall, they found that the effects of BPA exposure depends on the gender of the offspring, the dose, as well as the timing. The effects caused by fetal exposure were most severe, as compared to effects caused by later exposures (Liu et al. 2013).
A different study aimed to identify what dose and what timing were most important for BPA expsoure. It found that "both perinatal exposure alone and perinatal plus peripubertal exposure to environmentally relevant levels of BPA resulted in lasting effects on body weight and body composition. The effects were dose specific and sex specific and were influenced by the precise window of BPA exposure. The addition of peripubertal BPA exposure following the initial perinatal exposure exacerbated adverse effects in the females but appeared to reduce differences in body weight and body composition between control and BPA exposed males." Thus the effects varied by dose, sex, and timing (Rubin et al. 2016).
An interesting study exposed only the father rats to BPA, not the mothers, and looked for effects in both the fathers and offspring. The offspring did not show metabolic effects, but the fathers did. The father rats, who were exposed to the supposedly "safe" dose of BPA over a number of weeks, showed disrupted blood glucose control and pancreatic function (but not body weight). A high fat diet worsened these effects (Ding et al. 2014).
Some studies have tried to determine the specific mechanisms by which fetal and early-life BPA exposure can induce insulin resistance and diabetes later in life. For example, Ma et al. (2013) found that at 21 weeks of age, rats exposed to BPA (while in the womb and nursing) had higher insulin resistance and insulin levels than unexposed controls (just as other studies have found). None of these effects were apparent earlier in life, at 3 weeks of age. However, the researchers did find abnormal epigenetic changes that were not apparent in the controls, which suggests that these changes may play a role in later development of insulin resistance. And again, these rats were exposed to the U.S. EPA's supposed "safe" dose of BPA. Additional studies are now identifying the specific epigenetic changes that may explain BPA's affect on metabolism (Anderson et al. 2016).
Alarmingly, the epigenetic effects of BPA have also been shown to sometimes pass from one generation to the next (Singh and Li, 2012).
Another study looked at metabolic changes in mice exposed to BPA early in life at 2 days and 3 weeks of age. Their tissues showed differences even at this early age, including in levels of glucose, that suggested BPA induced changes in whole body metabolism (Cabaton et al. 2013).
An alarming study of developmental exposure to mixtures of chemicals tested a mixture of BPA and two types of phthalates (DEHP and DBP), both found in plastics. Pregnant rats were exposed to this mixture, and outcomes evaluated in their offspring, for 3 generations. The third generation offspring (the exposed mothers' great-grandchildren), had higher rates of obesity (in addition to many other health issues). The mechanism involved not changes to DNA, but epigenetic changes that were passed down from one generation to the next (Manikkam et al. 2013). You can listen to a recording of a call with one of the authors of this study, Transgenerational Effects of Prenatal Exposure to Environmental Obesogens in Rodents, sponsored by the Collaborative on Health and the Environment.
An additional study found that when pregnant and lactating rodents were exposed just to BPA, their grandchildren had impaired glucose tolerance and insulin resistance-- even though those grandchildren were not directly exposed to BPA. These effects were passed down via the sperm (Li et al. 2014). In another study, the same authors confirmed that the effects were passed through the male line, and found that the effects of BPA also included beta cell dysfunction (in addition to glucose intolerance). Epigenetic mechanisms probably are involved (Mao et al. 2015). And an additional study in mice has also found that BPA exposure in the womb led to higher body fat and disturbed glucose levels in male children and grandchildren (but not female offspring) (Susiarjo et al. 2015).
BPA also has transgenerational effects, passed through the male line, that impede development of the heart and increase heart failure for a few generations, in addition to affecting insulin signalling in zebrafish (Lombó et al. 2015).
Researchers exposed pregnant mice to BPA at a range of different levels, ranging from 10 times lower than the EPA's "safe" dose to 10 times above the EPA's predicted "No Adverse Effect Level (NOAEL)." They found that at doses below the NOAEL, there were significant effects in the adult male offspring (just as other studies have found), including lower glucose tolerance, increased insulin levels and insulin resistance, higher food intake, higher body weight, more abdominal fat, and more. For most of these effects, the dose-response curve was non-linear. At the highest dose studied, there were no significant effects (Angle et al. 2013). This is a very interesting study, not only because it finds significant effects at low doses, but also because the effects at low doses are worse than at high doses. That may be in part due to the way the body reacts to hormones (and BPA is a hormonally active endocrine disruptor); when the body encounters high levels of a hormone, it reduces its cellular receptors to that hormone. The authors conclude that "the dose does not make the poison," that is, that very high doses do not necessarily have a greater effect than very low doses (Angle et al. 2013). For an article about this study, see Mice harmed by low doses of BPA but not high doses, study says, published by Environmental Health News.
Other authors explain that BPA (and BPS) have mechanisms of action that explain why they are very potent at very low doses (Nadal et al. 2017).
Exposure to BPA in utero and in early life may affect the body weight of animals, depending on dose and gender (Rubin and Soto 2009). One study, for example, found that exposure to a low dose of BPA during gestation and lactation increased the body weight of rats. The effects varied by age, gender, and diet (Somm et al. 2009). Another study found that exposure to BPA during gestation and lactation led to increased body weight and height after weaning in mice (as compared to controls), but that these difference disappeared by adulthood (Ryan et al. 2010). And yet another study found that early life BPA exposure was not associated with changed body weight in exposed mice, although body fat and weight were lower than controls in female mice of certain ages (Anderson et al. 2013). Juvenile rats exposed to BPA did not have different body weights later in life than unexposed rats, although the exposed rats did develop more fat in their liver than the unexposed rats (Rönn et al. 2013).
In alligators, BPA exposured babies grew more quickly in early life but more slowly thereafter. They were fatter than unexposed controls at 5 weeks but then leaner at 21 weeks of age (Cruze et al. 2015).
Thus you can see that different studies have found different things. These differences may be due to a variety of factors, including the species studied, gender, the amount of BPA used, the timing/duration of exposure, diet/nutrition, etc. According to a review of the evidence, vom Saal et al. (2012) argue that these differences may also be explained by laboratory practices, e.g., measuring body weight instead of the more accurate body fat, making sure control animals are not inadvertently exposed to BPA or other estrogenic chemicals (e.g., via water bottles or cages), or feeding rodents soy-based chow that does not contain variable amounts of plant-based estrogens.
Another factor is exercise-- interestingly, female mice exposed to BPA during development participated in less physical activity than controls. They also had altered metabolism of carbohydrates and fats (Johnson et al. 2015).
What are the effects of mixtures of chemicals? Very few studies have been done on chemicals in combination with one another, although that is how humans are exposed. One study exposed mice -- starting from before conception -- throughout life to very low doses (at levels thought to be "safe") of a combination of chemicals commonly found in food, including phthalates, BPA, dioxin, and PCBs, and fed them a high-fat diet. As adults, compared to unexposed controls, pollutant-exposed females developed impaired glucose tolerance, and males showed liver and cholesterol effects, as well as epigenetic changes (Naville et al. 2013). The same authors subsequently fed mice a high-fat, high-sugar diet, both with and without this same low-dose mixture of chemicals. This time, the chemical-exposed females showed improvement in glucose tolerance, inflammation, and insulin resistance at 7 weeks of age, but then worsening of these factors at 12 weeks of age. Thus the chemicals cause at first an apparent improvement, then a worsening as aging takes place (as compared to the mice fed the same diet but without chemicals) (Naville et al. 2015).
One rodent study has found that procyanidin A2, a chemical found in some plant foods (like avocado, cinnamon, cranberry) can help prevent the effects of BPA in mice. For example, it can prevent the death of insulin-producing cells that BPA causes, and also reduces high blood sugar caused by BPA (Ahangarpour et al. 2016).
In a rat study, maternal exposure to BPA induced pancreatic impairments in the offspring, which included disrupted insulin secretion, glucose intolerance, and impaired structure of beta cells. However, maternal folate supplementation counteracted the pancreatic effects of BPA (Mao et al. 2017).
Beta cells are the cells in the pancreas that produce insulin. Studies show that BPA affects the production and activity of insulin by pancreatic beta cells. These effects have been seen in studies using human beta cells as well as mouse beta cells, at levels comparable to those humans encounter (Soriano et al. 2012). A study of rat beta cells shows that low levels of BPA (and other estrogenic chemicals) affect insulin secretion and disrupt beta cell function (Song et al. 2012). A study that compared BPA to other chemicals found that only BPA affected insulin secretion in mouse beta cells (Makaji et al. 2011). The effects of BPA are similar in mouse and human beta cells, and were significant even at very small doses, the doses that we are exposed to in the environment (Soriano et al. 2012). The mechanisms by which BPA can promote insulin resistance and impaired glucose tolerance are known in mice, and the ability of BPA to have the same effects on human beta cells implies that at least some of these effects are also applicable to humans (Soriano et al. 2012).
A study that aimed to determine the mechanisms by which BPA affects beta cells found that BPA suppressed cell viability and disturbed insulin secretion. Eventually, the beta cells died. The authors found that BPA affected the mitochondria in the cells, leading to these effects (Lin et al. 2013). BPA has also been found to damage DNA in pacreatic beta cells, in conjunction with oxidative stress (Xin et al. 2014). It also may affect beta cells by affecting ion channels (Soriano et al. 2016).
Low dose exposure to BPA damaged beta cells, eventually leading to their death. BPA in combination with the stress of high glucose levels led to a reduced ability of beta cells to respond to damage (Carchia et al. 2015).
An interesting study found that BPA was more potent than phthalates in reducing beta cell function. Both BPA and the phthalate metabolites reduced beta cell viability after 72 hours of exposure, with BPA the most potent. Both BPA and the phthalate metabolites increased insulin secretion after 2 hours of simultaneous exposure to the chemicals and glucose, with BPA again the most potent. However, neither BPA nor phthalates affected susceptibility to beta cell death. And, unlike other studies, low level exposures did not show effects (Weldingh et al. 2017).
Long-term, high dose exposure to BPA, as well as another phenol chemical, nonylphenol, promotes insulin secretion from the pancreatic islet cells in rats. Nonylphenol is used in some personal care products, pesticides, detergents, and paints (Adachi et al. 2005). (Nonylphenol also promotes obesity in mice (Hao et al. 2012).)
BPA has also been found to affect another hormone (besides insulin) that is released from beta cells (the hormone is human islet amyloid polypeptide, if you really want to know). Aggregation and misfolding of this hormone can lead to beta cell death, and indeed, BPA was found to exacerbate its aggregation in beta cells (Gong et al. 2013).
Beta cells are not the only types of cells affected by BPA. Using pre-fat cells from people with a normal body mass index (BMI), researchers found that exposing these cells to BPA induced them to turn into (differentiate) fat cells and accumulate fat (Boucher et al. 2014). A different lab also found that BPA enhanced the ability of human pre-fat cells to differentiate into fat cells, at levels that humans are exposed to (Ohlstein et al. 2014). Another study also found that BPA promoted adipogenesis in pre-fat cells (but not stem cells). These authors also found that a related compound, bisphenol A diglycidyl ether (BADGE), a BPA derivative, induced adipogenesis in both pre-fat cells and stem cells, at levels comparative to those found in humans (Chamorro-García et al. 2012). Another study using human fat cells found that low doses of BPA cause inflammation in fat cells, and inhibits glucose utilization, which lead to impaired fat cell function (Valentino et al. 2013). This lab also found that pre-fat cells cultured with low doses of BPA for 3 weeks showed increased pre-fat cell proliferation. Mature fat cells held more fat, had impaired insulin signalling, and reduced glucose utilization (Ariemma et al. 2016).
In children's fat cells, BPA promotes inflammation and the expression of genes linked to lipid metabolism, and decreases the expression of a gene linked to insulin production (Menale et al. 2015). Another study of children's fat cells found that even at the lowest exposure level, BPA activated an enzyme that promotes conversion of pre-fat cells to fat cells (adipogenesis), and also affected gene expression (Wang et al. 2013).
Ben-Jonathan et al. (2009) reviews earlier studies of BPA's effects on fat cells. For example, BPA has been found to affect the transport of glucose in the fat cells of mice, which could have implications for the development of diabetes (Sakurai et al. 2004). BPA increases the deposition of lipids in fat cells, which could increase the likelihood of metabolic syndrome (Wada et al. 2007). BPA also promotes the development of fat cells (Masuno et al. 2002).
Scientists are now working to identify the mechanisms by which BPA can affect fat cell development (Xie et al. 2016; Boucher et al. 2014). For example, BPA can promote the development of fat cells from rodent pre-fat cells even under less-than-ideal conditions (Atlas et al. 2014).
BPA is also capable of acting like other hormones besides estrogen, by binding with various other hormone receptors (just like it binds with estrogen receptors). For example, it can promote the formation of fat cells by activating glucocorticoid hormone receptors, which play a role in glucose metabolism (Sargis et al. 2010). In addition, exposure of human tissues to low doses of BPA inhibits the release of a hormone (adiponectin) that increases insulin sensitivity and reduces tissue inflammation. Any factor that inhibits this hormone's release could lead to insulin resistance (Hugo et al. 2008). BPA also has other effects on fat cells that may lead to insulin resistance (Dai et al. 2016).
Some compounds that are related to BPA and used as flame retardants can activate PPARγ (peroxisome proliferator-activated gamma receptor), which play a role in glucose metabolism as well as fat storage. In one study, BPA, however, did not activate PPARγ receptors Riu et al. 2011), but in another, it did (Biasiotto et al. 2016). For an article on the Riu study on halogenated BPA flame reatardands, see Warm reception? Halogenated BPA flame retardants and PPARγ activation, published by Environmental Health Perspectives (Barrett 2011). Another study, of zebrafish, also found that developmental exposure to these compounds promotes fat accumulation in larvae and weight gain in the juvenile fish (Riu et al. 2014).
And, as discussed in the type 1 diabetes section below, BPA can affect immune cells as well.
BPA is often thought to break down to harmless metabolites in the body. However, a study shows that these metabolites may not be harmless at all. Pre-fat cells treated with the metabolite BPA-Glucuronide (BPA-G) showed increased fat cell formation (Boucher et al. 2015). For two articles describing this study, see Do our bodies safely break down BPA? Fat chance, study suggests, published by Environmental Health News, and Unexpected activity: Evidence for Obesogenicity of a BPA Metabolite, published by Environmental Health Perspectives (Nicole, 2015).
Two studies have found that BPA exposure accelerates insulitis and diabetes development in non-obese diabetic (NOD) mice, an animal model of type 1 diabetes (Bodin et al. 2013 and Bodin et al. 2014). The first study found that long-term exposure to BPA at relatively high levels accelerated insulitis in NOD mice. The second found that exposing mothers to BPA caused their female offspring to have more severe and higher incidence of insulitis. The authors write, "In conclusion, transmaternal BPA exposure, in utero and through lactation, accelerated the spontaneous diabetes development in NOD mice. This acceleration appeared to be related to early life modulatory effects on the immune system, resulting in adverse effects later in life." (Bodin et al. 2014).
BPA has been shown to affect the immune system of rodents in ways that may be significant for autoimmune diseases. In genetically susceptible mice, BPA enhances the production of autoantibodies. While this study used higher doses than humans are probably exposed to, further studies should be able to determine if these effects also occur at lower doses. The authors conclude that BPA may be a factor in the increased incidence of autoimmune disease in humans. Both estradiol, a natural estrogen, and the estrogenic pharmaceutical diethylstilbestrol (DES) showed the same autoimmune-enhancing effects as BPA (Yurino et al. 2004). Laboratory studies also show that BPA can affect the immune system of animals (e.g., Qiu et al. 2016). Because BPA exposure can influence the immune system, BPA is considered to be an immunotoxicant (desribed on the autoimmunity page (Dietert and Dietert 2007) and a risk factor for autoimmune diseases (Jochmanová et al. 2015). BPA has been associated with thyroid autoimmunity in humans, for example (Chailurkit et al. 2016).
BPA also affects adult rodents' response to infection, and patterns of immune system cells called cytokines. Rodents exposed to BPA in utero showed an increased immune response as adults, with higher levels of certain cytokines. BPA's ability to disturb cytokine production in animals could influence inflammation; cytokines are discussed further on the inflammation page. The effects of BPA on the immune system of rodents depend on the timing of the exposure as well as gender (Richter et al. 2007). Oxidative stress is another mechanism likely involved in the effects of BPA on the immune system. Zebrafish embryos, a model used to screen for toxicity in the lab, show a higher immune response when exposed to BPA (and nonylphenol), involving altered immune gene expression and oxidative stress (Xu et al. 2013). Studies of other autoimmune diseases, e.g., SLE (lupus), show that BPA can induce immune signalling that may potentiate these diseases (Panchanathan et al. 2015). BPA can also trigger neurological autoantibodies (Kharrazian and Vojdani, 2016).
Numerous types of immune cells have been found to be affected by BPA, including T cells, regulatory T cells, B cells, dendritic cells, and macrophages (reviewed in Rogers et al. 2013). In fact, "virtually all the major cells of the immune system" are affected by BPA, and these pathways may be one way that autoimmune diseases are promoted by BPA (Kharrazian 2014). Many of these cells are involved in inflammation and human disease, including autoimmune disease such as type 1 diabetes. BPA has been found to specifically augment the Th1 immune response, which is linked to autoimmunity (Goto et al. 2007). Developmental expousre BPA also affects levels of Th17 cells, also linked to autoimmunity (Luo et al. 2016).
Does BPA interact with viruses?
In humans, exposure to BPA has been associated with higher levels of cytomegalovirus antibodies in adults, a sign of altered immune system function. In youth, BPA exposure was associated with lower cytomegalovirus antibody levels. It is unclear what could account for these differences. The authors of this study suggest that perhaps the consequences of BPA exposure may vary depending on the timing, quantity, and duration of exposure. Perhaps short exposures stimulate the immune system, and longer exposures result in immune dysfunction (Clayton et al. 2011).
In rats, early life exposure to BPA made them more susceptible to intestinal infection than those unexposed, and impaired their ability to respond to food antigens (Ménard et al. 2014). Intestinal infections and food antigens are both linked to type 1 diabetes (see the diet and the gut page). Laboratory evidence also indicates that BPA detrimentally alters gut microbiota (Javurek et al. 2016, Koestel et al. 2017; Lai et al. 2016). Gut microbiota are also linked to diabetes development. And, BPA causes intestinal cells to absorb more cholesterol (Feng et al. 2017).
A study of a mouse model of Multiple Sclerosis (MS), another autoimmune disease, found that BPA exposure in combination with a virus had numerous effects on these mice, including an acceleration of symptoms, increased inflammation, and changes in immune-related gene expression (Brinkmeyer-Langford et al. 2014).
Does BPA influence vitamin D levels? One cross-sectional study of U.S. adults found that women with higher BPA levels have lower vitamin D levels (Johns et al. 2016). Low vitamin D levels are linked to diabetes development (see the vitamin D page). I expect this finding will encourage additional research on the topic.
A study found that when pregnant mice were exposed to low and high doses of BPA, their insulin resistance increased, and glucose tolerance decreased during the pregnancy (especially those exposed to the lower doses). Four months after the birth, they had increased insulin resistance and also weighed more than the untreated control mice (without differences in food intake). Interestingly, the effects were not apparent three months after the birth, but reappeared at four months. The results suggest that BPA could contribute to the development of gestational diabetes (Alonso-Magdalena et al. 2010). Another study by the same authors found that mother mice treated with low doses of BPA during pregnancy developed glucose intolerance, increased body weight, and insulin resistance, decreased insulin secretion, reduced beta cell mass, and increased beta cell death, several months after delivery (Alonso-Magdalena et al. 2015). These factors are important for a mother's development of diabetes following pregnancy (mothers commonly develop type 2 following gestational diabetes; I developed type 1 following gestational diabetes-- it does happen!)
Two human studies have not found links between BPA and gestational diabetes, however. One study done in Oklahoma did not find an association between pregnant women's BPA levels and gestational diabetes or fasting blood glucose levels (Robledo et al. 2013). Another study from Canada also did not find an association between BPA and gestational diabetes (although it did find an association between arsenic and gestational diabetes) (Shapiro et al. 2015).
A study from the Boston area, however, found that BPA levels during the second trimester (but not the first) were associated with glucose levels in women from a fertility clinic (Chiu et al. 2017).
BPA exposure during pregnancy is associated with inflammation and oxidative stress in mothers (Ferguson et al. 2016); perhaps these mechanisms could help explain the health effects of BPA on both mother and child.
People with type 2 diabetes who had higher levels of BPA in their bodies had a 7-fold (!) higher risk of developing chronic kidney disease than those with lower levels. That number is from a study of Chinese adults who were followed for 6 years (Hu et al. 2015). This finding deserves some attention!
Also, people with diabetes undergoing dialysis have measurably higher BPA levels in their blood after a single dialysis session that before the session, implying that dialysis itself is a source of BPA exposure. Those with diabetes also had higher BPA levels than those without diabetes (Neri 2016; Turgut et al. 2016).
BPA elimination is impaired in individuals with diabetes, obesity, or fatty liver, as shown in studies with human and mouse liver samples. The liver metabolizes BPA and leads to its elimination from the body (Yalcin et al. 2015).
Melzer et al. (2010) and Lang et al. (2008) found that BPA is associated with heart/cardiovascular disease in the general U.S. population. In fact, numerous human studies have shown that higher BPA concentrations in humans are associated with various types of cardiovascular diseases, including angina, hypertension, heart attack, and coronary and peripheral arterial disease (e.g., Aekplorn et al 2015; Han and Hong 2016, and earlier studies reviewed in Gao and Wang 2014). In Chinese adults, BPA is also associated with albuminuria (protein in the urine), a common complication of diabetes (Li et al. 2012). And in Iranian adults, those with higher levels of BPA had higher average blood glucose levels (higher HbA1c) (Ahmadkhaniha et al. 2014). In Ohio children, BPA levels were associated with higher blood pressure and other adverse liver and metabolic changes (Khalil et al. 2014). In U.S. and Korean adults, BPA exposure was associated with hypertension (high blood pressure) as well (Bae et al. 2012; Shankar and Teppela, 2012). And in those with hypertension, BPA is associated with the development of kidney disease (Hu et al. 2016). In animals, BPA affects the heart muscle (Preethi et al. 2017).
BPA is also linked to obstructive sleep apnea, common in people with diabetes, obesity, or metabolic syndrome. People with severe sleep apnea were found to have higher levels of BPA (and lower levels of vitamin D) (Erden et al. 2014).
Elderly adults who consumed two beverages out of cans containing BPA had significantly higher blood pressure two hours later, as compared to when they drank beverages out of glass (Bae and Hong, 2015).
In animals, mice chronically exposed to BPA and a high-fat, high-cholesterol diet showed accelerated atherosclerosis as compared to control mice who ate the same diet but were not exposed to BPA. The exposed mice also had higher levels of non-HDL cholesterol than controls (Kim et al. 2014). Animal studies show that BPA causes atherosclerosis and high blood pressure in rodents (reviewed in Gao and Wang 2014, or specific studies such as Saura et al. 2014).
Adult exposure to BPA causes fatty liver in animals (Yang et al. 2017); early-life exposure to BPA also enhances non-alcoholic fatty liver disease in animals, especially in combination with a high fat diet (Wei et al. 2014; Strakovsky et al. 2015). Fetal exposure also affects fetal development of the liver in mice (DeBenedictis et al. 2016). BPA exposure from birth through young adulthood affects heart function and blood pressure in mice, with females at greater risk (Belcher et al. 2015). It affects heart function in sheep as well (MohanKumar et al. 2016). Exposure to BPA during development affects fatty acid levels in mice (Veiga-Lopez et al. 2015). BPA also has detrimental effects on the heart (Ljunggren et al. 2016), and makes it harder for animals to recover from a heart attack (Patel et al. 2015)
BPA can also cause "brain insulin resistance" in mice, which is a condition linked to Alzheimer's disease (Fang et al. 2015).
A systematic review and meta-analysis of 33 large human studies concluded that, "there is evidence from the large body of cross-sectional studies that individuals with higher BPA concentrations are more likely to suffer from diabetes, general/abdominal obesity and hypertension than those with lower BPA concentrations.... Moreover, among the five prospective studies, 3 reported significant findings, relating BPA exposure to incident diabetes, incident coronary artery disease, and weight gain" (Rancière et al. 2015).
Another review summarizes "both epidemiological evidence and in vivo experimental data that point to an association between BPA exposure and the induction of insulin resistance and/or disruption of pancreatic beta cell function and/or obesity" (Chevalier and Fénichel 2016). An additional review, of 13 studies on type 2 diabetes and BPA argues that, "chance is unlikely the plausible explanation for the observed association" between BPA exposure and type 2 (Sowlat et al. 2016).
Another review finds that "Most data support the effects of bisphenol A ... on the development obesity and type 2 diabetes mellitus. These endocrine disrupting chemicals interfere with different cell signaling pathways involved in weight and glucose homeostasis." (Stojanoska et al. 2016). An additional review finds that "Most of the clinical observational studies in humans reveal a positive link between BPA exposure, evaluated by the measurement of urinary BPA levels, and the risk of developing type 2 diabetes mellitus. Clinical studies on humans and preclinical studies on in vivo, ex vivo, and in vitro models indicate that BPA, mostly at low doses, may have a role in increasing type 2 diabetes mellitus developmental risk, directly acting on pancreatic cells, in which BPA induces the impairment of insulin and glucagon secretion, triggers inhibition of cell growth and apoptosis, and acts on muscle, hepatic, and adipose cell function, triggering an insulin-resistant state." (Provvisiero et al. 2016).
For a nice (and free full text) review of the evidence linking prenatal BPA exposure to diabetes and obesity, see Alonso-Magdalena et al. 2015.
So why is BPA still legal to use? It is beyond me. Ask the FDA.
To download or see a list of all the references cited on this page, see the collection BPA and diabetes/obesity in PubMed.