Links Between Breastfeeding and Diabetes/Obesity
Breastfeeding has links to a lower risk of type 1 diabetes, type 2 diabetes, and obesity in offspring, and benefits for the mother as well, including a lower risk of metabolic syndrome and type 2 diabetes. Some authors suggest that exclusive and prolonged breastfeeding might help prevent type 1 diabetes by supporting the immune system (Xiao et al. 2017).
However, the evidence is not always consistent. If breastfeeding is not possible, try not to worry about it, since the evidence is far from overwhelming that it actually does reduce the later risk of diabetes.
World Health Organization (WHO) infant feeding guidelines call for exclusive breastfeeding for a full 6 months, the introduction of safe and complementary foods from the sixth month of life while breastfeeding continues, and then continued breastfeeding for up to 2 years of age or beyond. Only 5% of families of children with first degree relatives who have type 1 diabetes follow the WHO recommendations for infant feeding (Pflüger et al. 2010), and mothers with type 1 diabetes tend to breastfeed their children less than other mothers, and less than WHO recommends (Hummel et al. 2007).
Type 1 Diabetes
While breastmilk may be the best food for a baby, can it also lower the risk of that baby developing type 1 diabetes?
A meta-analysis of the data from 43 studies found "weak" protective associations between exclusive breastfeeding (i.e., with no added formula) and later development of type 1 diabetes. It was difficult to analyze the data, however, due to differences among studies (Cardwell et al. 2012).
A systematic review of 28 studies found that lack of breastfeeding or a too-short duration of breastfeeding may be a risk factor for the development of type 1 diabetes later in life (Patelarou et al. 2012). A systematic review of dozens of studies by the U.S. Department of Health and Human Services found the same thing (Güngör et al. 2019).
An analysis of data from 17 earlier studies found moderately increased incidence of type 1 diabetes in infants given formula before 3 months of age. Yet they also found that studies that depended on parental recall showed breastfeeding to be more protective than the other studies. These and other methodological differences may explain the differing results (Norris and Scott 1996).
A retrospective study found that longer exclusive and total breastfeeding was protective against type 1 diabetes in a group of Swedish and Lithuanian children, regions of high and low incidence of type 1 respectively (Sadauskaite-Kuehne et al. 2004). Another retrospective study in Germany also found breastfeeding protective (Rosenbauer et al. 2007), as did a Brazilian study (Alves et al. 2012).
Some prospective studies have not found breastfeeding to be protective:
A German study found no differences in type 1-related autoantibody risk related to the duration of exclusive or total breastfeeding in children genetically at risk of type 1 diabetes (the children were followed until age 8) (Ziegler et al. 2003).
An Australian study of genetically at-risk children also found that the duration of total or exclusive breastfeeding was not associated with the risk of developing type-1 related autoantibodies (Couper et al. 1999).
And, a U.S. study also did not find breastfeeding to be protective against the risk of developing autoantibodies in genetically at-risk children (Norris et al. 2003). Interestingly, however, this study found that if cereals were introduced while the child was still breastfeeding, the risk of autoimmunity was lower (see the wheat and dairy page).
In children genetically at risk for type 1 diabetes in the large, international TEDDY study, longer breastfeeding was not associated with a lower risk of childhood diabetes or celiac disease related autoimmunity (but was associated with decreased risk of allergies and obesity at 5.5 years of age) (Hummel et al. 2021).
However, other prospective studies have found breastfeeding to be protective:
A large population-based study using data from Norway and Denmark found that children who were never breastfed had twice the risk of type 1 diabetes compared to those who were breastfed. The length of time breastfeeding or full breastfeeding did not make a difference (Lund-Blix et al. 2017).
A prospective study of the general population has found breastfeeding to be protective: a study from Sweden found that longer term breastfeeding was protective against type 1-related autoimmunity, even in 5 year olds, in children who were not necessarily at high genetic risk of developing the disease (Holmberg et al. 2007).
A prospective study from Finland found that the more breastmilk consumed, the lower the risk of type 1 diabetes-related autoimmunity (Niinistö et al. 2017).
A prospective Norwegian study of genetically susceptible children found breastfeeding of at least 12 months to reduce the risk of progression from autoimmunity to the development of type 1 diabetes (Lund-Blix et al. 2015).
A U.S. prospective study found that breastfeeding at the time of introducing wheat or barley was protective against later type 1 diabetes development (Fredericksen et al. 2013).
Breastfeeding may interact with other factors, e.g., daycare attendance (a proxy measurement of exposure to infections). Children at genetic risk of type 1 and attended daycare had a higher risk of type 1 if not breastfed, but a lower risk if breastfed (Hall et al. 2015).
And some studies are still unclear:
A prospective study of a group of Finnish children, followed from birth, found that infants with genetic risk of developing type 1 diabetes who had been exclusively breastfed for at least 4 months had a lower risk of developing type 1-associated autoantibodies than did infants exclusively breastfed for less than two months (Kimpimäki et al. 2001). Yet a more recent study by the same authors found that breastfeeding was not associated with the development of beta cell autoimmunity (Virtanen et al. 2006).
The Immune System
So what is going on here? Breastmilk contains numerous protective immunological and anti-inflammatory factors (see the inflammation page), may support the maturation of the intestine (see the diet and the gut page), and may enhance thymus size (see the autoimmunity page for more on the thymus), and thereby potentially help a child's immune system develop properly (Jackson and Nazar 2006). In fact, breastmilk has more influence on an infant's microbiome than other factors studied (Stewart et al. 2018). Breastfeeding also has been shown to protect against enterovirus infections during infancy, and these infections are a likely trigger of type 1-related autoimmunity (see the viruses page) (Knip et al. 2010). Breastmilk contains numerous bioactive substances that may be protective against type 1 diabetes (Yahaya and Shemishere 2020). Breastfeeding also decreases the likelihood of obesity in the offspring of mothers with diabetes of any type (Feig et al. 2011). It would seem to make sense, then, that breastfeeding might be protective against type 1 diabetes.
So why, then, are there inconsistent results to these studies on breastfeeding and type 1 diabetes? Some of the reasons that might help explain the inconsistent results of these studies follow. One, exclusively breastfed infants are at higher risk of vitamin D deficiency than are formula-fed infants. This deficiency can be remedied. During pregnancy, the fetus will maintain sufficient vitamin D levels if the mother has sufficient levels of vitamin D, which may require supplementation. After birth, the mother may need up to 4000 IU per day to maintain sufficient levels in her and her exclusively breastfed baby (Kovacs 2008). Vitamin D deficiency may contribute to the development of type 1 diabetes (see the vitamin D page). Two, just because breastmilk contains a number of immune system factors that can protect against infection in early life does not necessarily mean that these factors would be able to influence the development of disease later in life (Jackson and Nazar 2006). In other words, we might be expecting too much. A third, more troubling possibility, is that environmental chemicals may play a role in compromising the protective effects of breastmilk. Read on for some evidence supporting this possibility.
Breastfeeding and Environmental Chemicals
One possible reason for the conflicting results in the studies on type 1 diabetes and breastfeeding is the method of delivery of milk or formula. None of these studies have looked at whether the babies receive breastmilk directly from the breast, from a glass bottle, or from a plastic baby bottle. Was pumped breastmilk stored in plastic? Was the milk or formula heated in plastic? Toxic chemicals such as BPA can leach out of plastic baby bottles, especially when heated (De Coensel et al. 2009). Some of the chemicals found in plastics affect animals in ways that imply they could potentially contribute to the development of type 1 diabetes in humans (see the BPA and phthalates pages, for example). Researchers conducting studies on breastmilk vs. formula might consider controlling for the method of milk delivery, which bottles were used, how often, and how the milk was stored and heated. Mothers could use glass bottles; in my experience they are sturdy and do not break easily.
And then there's the milk itself. Breastfed children are exposed to higher levels of some environmental chemicals than those who are not breastfed. In a study of German 10 year olds, for example, breastfeeding was one of the strongest factors influencing the concentration of persistent organic pollutants (POPs) in their bodies. Breastfeeding was associated with about 30% higher median concentrations of various POPs (DDE, HCB, PCBs), and breastfeeding for 6 months doubled the concentrations of DDE and PCBs compared to children who were not breastfed. These findings are consistent with other studies as well (Link et al. 2005). In Norway, every month of breastfeeding increased children's level of PFASs by 3-6% (Papadopoulou et al 2016). However, note that some chemical levels, including some heavy metals and BPA, are lower in breastmilk than in formula (Martínez et al. 2019).
Lactation, meanwhile lowers the chemical levels in the mother-- and also a lower risk of diabetes in the mother (Zong et al. 2016). Losing weight while breastfeeding does increase POP levels in the milk, but the estimate average intake of POPs by the babies stayed the same since over time they drink less milk (Lignell et al. 2016).
Levels of various POPs in lactating women are also associated with levels of leptin and adiponectin their breastmilk, hormones that play a role in metabolism. Whether this would affect the growth of infants we don't know, but it is a possibility (Kim et al. 2015). In mother rats, lead exposure led to lower levels of omega 3 fatty acids in their breastmilk (Hossain et al. 2019); omega 3s may be protective against type 1 diabetes (see the Nutrition page).
Weisglas-Kuperus et al. (2004) found that some of the expected protective effects of breastfeeding on the immune system were counteracted by the negative effects of higher perinatal PCB exposure in Dutch children exposed to normal, background levels of contamination.
In another study of Dutch children, breastfeeding for six months was found to make up 12-14% of the children's cumulative exposure to PCBs and dioxins until age 25. Yet since in utero exposures are likely to have more severe effects than those via breastfeeding, and since the benefits of breastfeeding still outweigh the negatives, this finding should not be a reason to reduce breastfeeding (Patandin et al. 1999).
Chemical levels in mothers' bodies may also affect their capability to breastfeed. For example, two studies have found that women who have higher levels of PFAS (especially PFOA and PFOS) breastfed their babies for a shorter duration than those who had lower exposure levels (Romano et al. 2016; Timmermann et al. 2017). A review of this topic finds that both PFAS and BPA are linked to reduced breastfeeding duration, and that other chemicals, including phthalates and pesticides, affect mammary gland development (Criswell et al. 2020).
Chemical levels also can influence the nutritional quality of breastmilk. PFAS levels were linked to detrimental changes in breastmilk, which were in turn associated with slower infant growth and more intestinal inflammation in the infants (Lamichhane et al. 2021).
Chemical levels in mothers' bodies may also affect the gut microbiome of their infants. For example, levels of various POPs (including PCBs, PBDEs, and PFASs) in breastmilk were were associated with less microbiome diversity and with microbiome functionality in 1 month old infants (Iszatt et al. 2019). Exposure to environmental pollutants (metals, PFAS, pesticides) in women is associated with alterations in gut microbiome development in their infants. Associations were affected by mode of birth (C section vs vaginial), breastfeeding, and fetal exposure time (Naspolini et al. 2021). The gut microbiome is linked to the development of diabetes, especially type 1 diabetes (see the Diet and the Gut page). Exposure to the POP hexachlorocyclohexane (HCH) alters the microbiome of colostrum in breastfeeding mothers (Tang et al. 2019). Some have tried to see if taking probiotics while breastfeeding reduces the infant's exposure to chemicals; the results aren't clear yet, although this was a small study and this topic will be interesting to follow (Astolfi et al. 2019).
A review finds that, "The available literature does not provide conclusive evidence of consistent or clinically relevant health consequences to infants exposed to environmental chemicals in breast milk at background levels." However, "A critical data gap is a lack of research on environmental chemicals in formula and infant/child health outcomes" (LaKind et al. 2018). An article that summarizes this and another review concludes that the benefits of breastmilk still outweigh the risks from chemicals in the milk (Arnold 2019).
Breastfeeding and the Mother's Diet
Another contributing factor to the various findings could be the mother's diet. Very few studies have considered what the mother eats while breastfeeding. One that did found that the more red meat and processed meat that the mother eats while breastfeeding, the higher the child's later risk of type 1 diabetes. Fatty acid consumption was not associated (Niinistö et al. 2015). Artificial sweeteners consumed by the mother are present in breastmilk; we don't know what effects these have on the infant or fetus (Sylvetsky et al. 2015).
The levels of meat, dairy, eggs, and fish in a mother's diet do appear the affect the POP content of her breastmilk. Also, the levels are higher early in breastfeeding and decline as lactation continues (Witczak et al. 2021).
Consumption of canned drinks increases the levels of BPA in mother's milk. In turn, BPA levels in milk (as well as levels of heavy metals) were linked to a different immunological profile of the milk (Castro et al. 2021).
Type 2 Diabetes and Body Weight
Type 2 Diabetes in Mothers
A review states that, "In the mother, breastfeeding has been suggested to reduce the incidence of type 2 diabetes, the metabolic syndrome and cardiovascular disease. Moreover, it appears to reduce the risk of premenopausal breast cancer and ovarian cancer. In the neonate and infant, among other benefits, lactation confers protection from future both type 1 and type 2 diabetes. Whether lactation protects women with gestational diabetes and their offspring from future type 2 diabetes remains to be answered" (Gouveri et al. 2011). A more recent review found that women with gestational diabetes who breastfed showed better metabolic and glucose levels for 3 months after they gave birth. A long-term study also found that breastfeeding for at least three months reduced the risk of type 2 diabetes and delayed type 2 for 10 years in women who had gestational diabetes, as compared to women with gestational diabetes who breastfed for less than 3 months (Much et al. 2014). Another review found that "Lactation is associated with a significantly reduced risk of maternal type 2 diabetes over the life course, particularly in women with gestational diabetes. The protective effect seems to increase with longer duration of lactation." (Pinho-Gomes et al. 2021).
Breastfeeding also can reduce the risk of metabolic syndrome (a cluster of conditions that is common in people with diabetes) in the mother (Blair et al. 2021; Choi et al. 2017). Previous studies have also sometimes found that breastfeeding is associated with a lower risk of type 2 diabetes in the mother (Gunderson et al. 2010). Newer studies also find that breastfeeding is protective against the later development of diabetes in women who had gestational diabetes (Gunderson et al. 2015; Ley et al. 2020).
A meta-analysis of four longitudinal studies found that the longer the breastfeeding, the lower the risk of type 2 diabetes in the mother (Jäger et al. 2014). A larger meta-analysis, of 9 studies, found that breastfeeding was associated with a lower risk of type 2 diabetes in women who had gestational diabetes (Tanase-Nakao et al. 2017). A 30 year long study found that breastfeeding was associated with a lower risk of diabetes in the mother, and the longer the mother breastfed, the more protective it was (Gunderson et al. 2018). The evidence, however, is limited, and stronger for type 1 diabetes than type 2 (Güngör et al. 2019).
Lactation, in both mice and humans, appears to improve pancreatic beta cell survival, mass, and function in the long-term, even years after breastfeeding stops (Moon et al. 2020).
Type 2 Diabetes and Insulin Resistance in Offspring
In children from India, where breastfeeding is the norm, longer breastfeeding (over 18 months) was protective against glucose intolerance in children at 9-10 years of age, and was associated with lower insulin resistance at 5 years of age (Veena et al. 2011).
Systematic reviews or meta-analyses have found that for the infants, breastfeeding is protective against later type 2 diabetes (Horta et al. 2015; Owen et al. 2006; Pereria et al. 2014). However, a large prospective study from Denmark found that other maternal and early-life factors could explain this association-- that breastfeeding was not the critical factor (Bjerregaard et a. 2019).
In children with type 1 and type 2 diabetes, those who were breastfed as infants did not have a different level of insulin sensitivity/insulin resistance during childhood (The et al. 2016).
Obesity in Offspring
A large study from 22 European countries found that compared to children who were breastfed for at least 6 months, the risk of being obese were higher among children never breastfed or breastfed for a shorter period (Rito et al. 2019).
According to a meta-analysis of 35 studies, breastfeeding promotion interventions do not really appear to affect growth in the infant (height or weight), although did result in a slightly lower body mass index (BMI) (Giugliani et al. 2015).
Breastfeeding has been found to be protective against weight gain later in life, in the children of women who had diabetes when pregnant (Crume et al. 2011c).
Systematic reviews or meta-analyses have found that for the infants, breastfeeding is protective against later obesity (Harder et al. 2005; Horta et al. 2015; Owen et al. 2005; Yan et al. 2014), as do numerous individual studies (e.g., Zheng et al. 2020).
In the U.S., in the offspring of women who had gestational diabetes, breastfeeding was protective against obesity, but only if offspring have a lower intake of sugar-sweetened beverages (breastfeeding is protective even in children who drink sugar-sweetened beverages if their mothers did not have gestational diabetes) (Vandyousefi et al. 2019).
To download or see all the references on this and other diet-related pages, including cow's milk, gluten, nutrition, and more, see the collection Diet, nutrition, gut, microbiome and diabetes/obesity in PubMed.