The U.S. National Toxicology Program (NTP) held a workshop to evaluate the scientific evidence on chemicals in diabetes and obesity, and published a review of the evidence: Role of environmental chemicals in the development of diabetes and obesity: A National Toxicology Program Workshop Report (Thayer et al. 2012) (They also have a website on the role of environmental chemicals in the development of diabetes and obesity). They found, “Overall, the existing literature was judged to provide plausibility, varying from suggestive to strong, that exposure to environmental chemicals may contribute to the epidemic of diabetes and/or obesity....Research on environmental chemical exposures and type 1 diabetes was very limited. This lack of research was considered a critical data gap.”
CHEM Trust has published a report, "A Review of the Science Linking Chemical Exposures to the Human Risk of Obesity and Diabetes," which is an excellent review of the evidence.
When I began this research, I had three basic questions. Here they are, along with the answers I found.
A number of environmental factors have been associated with the development of type 1 diabetes. It is not yet known which of these factors are responsible for the increasing rates of disease in children, but since many of these factors influence and interact with each other, multiple factors are probably involved. The hypotheses page describes a number of possible factors and how they may interact. Different factors may be operating in different populations and in different parts of the world, making generalizations difficult. It is also not clear whether type 1 diabetes incidence is also increasing in adults, or whether people are simply being diagnosed at younger and younger ages.
Nevertheless, there is evidence that a number of environmental factors can contribute to the development of type 1 diabetes, such as inadequate vitamin D levels, a leaky gut, high growth rates, viruses, perhaps stress, and, probably, exposure to some environmental contaminants. Many of these factors have changed over time, and could conceivably contribute to the increasing incidence of type 1 diabetes in children.
How could we find out what factors are contributing to the increasing incidence of type 1 diabetes in children? We would need to know what factors can contribute to the development of the disease, by following people over time before they develop the disease and keeping track of their environmental exposures. We could identify biological mechanisms whereby factors contribute to diabetes in animals, although animals are not quite the same as humans. And, if possible, intervention trials to prevent type 1 might also be feasible (e.g., by giving people vitamin D supplements, for example, to see if people with higher vitamin D levels have a lower risk of developing type 1 diabetes over time).
What is the evidence that environmental contaminants might have something to do with the increasing incidence of type 1 diabetes? While only a few environmental contaminant exposures have been associated with type 1 diabetes in studies of people (PCBs, air pollutants, some heavy metals, and nitrate/nitrite), most studies of type 1 have not included measures of environmental contaminant exposures. A number of contaminants have been associated with diabetes (type 2, gestational, or unspecified) in humans (see the environmental contaminants and potential mechanisms pages for a summary of these and the following associations). A number of contaminants have been associated with risk factors of type 1 diabetes, such as weight gain, in humans and animals. A number of contaminants have been found to affect beta cells, and to induce or exacerbate autoimmunity, inflammation, insulin resistance, or oxidative stress in animals and sometimes humans, all processes that may play a role in the development of type 1 diabetes.
While exposure to environmental contaminants is not traditionally thought to be a risk factor for type 1 diabetes, the weight of all this evidence suggests that there is certainly potential for contaminants to contribute to the development of type 1 diabetes. The historical patterns of contamination are consistent with historical patterns of type 1 diabetes incidence. Whether some or many environmental contaminants are contributing to the rising rates of disease in children remains unknown, but it is plausible and possible.
When I started reading these studies, I did not expect to find that type 2 diabetes may be linked to contaminants. Like most people, I thought that weight gain, a poor diet, and lack of exercise could explain the increasing rates of type 2. I now think, like many scientists, that contaminants probably play a role in the development of type 2 diabetes as well. The effects of contaminants may be exacerbated by obesity and other lifestyle factors, but lifestyle and genes alone do not account for all cases of type 2 or all of its increasing incidence. In fact, there is growing scientific evidence that contaminant exposures can contribute to the development of type 2 diabetes.
Consider that about 20% of adults with diabetes are not overweight or obese (Nguyen et al. 2010); gastric bypass surgery often leads to remission of type 2 diabetes even before any weight loss occurs (Pournaras et al. 2010); and in people with very low levels of contaminant exposures, obesity does *not* increase the risk of diabetes (Lee et al. 2006).
There is only preliminary evidence linking gestational diabetes to environmental contaminants (see the pesticides, arsenic, and bisphenol A pages). But since gestational diabetes is so common, and can increase the risk of type 1 or type 2 in the mother, more research should be devoted to the possibility that contaminants may affect the risk of gestational diabetes development.
Researchers suggest that both avoiding the intake of toxic chemicals, and increasing their elimination from the body, may help prevent or treat diabetes and other "diseases of civilization" (Lee et al. 2008 , Hennig et al. 2007). Hennig et al. (2007) discuss a number of possible ways to use nutrition and diet to both reduce exposure and increase elimination. The authors describe one case study where a person with insulin-dependent type 2 diabetes (possibly as a result of PCB poisoning) was treated and the diabetes resolved (over 2 years). Watkins et al. (2007) also provide suggestions, including increasing consumption of omega-3 fatty acids and flavonoids (like chocolate...). The Environmental Working Group provides information on how to avoid toxic chemicals in consumer products. Buying organic food, limiting animal fats, avoiding plastic food containers (especially heating food in plastic), limiting fish high in mercury; these are just some of the things you can do to reduce chemical exposures. Let me know if you try any of these strategies, and whether or not they appear to have any effect (better yet; document it with medical records if possible).
Did you develop type 1 diabetes following a chemical exposure? A number of people have emailed me who are in this situation; we may be able to work together to figure out what chemicals may be of concern. My email: firstname.lastname@example.org.
Most chemical exposures, however, are widespread, ongoing, and unavoidable. Societal action to reduce exposures may be necessary as well as individual actions, in order to really prevent disease on a population level.
This website focuses on the development of diabetes-- but what about managing diabetes and avoiding complications? I have found only one study linking contaminant exposures with diabetes management. Lee et al. (2008) found that people with higher levels of various persistent organic pollutants (POPs), specifically organochloride pesticides, had higher hemoglobin A1c levels (a measure of long term glucose control) and more neurological complications. This finding could be really important for people with diabetes, and deserves more study.
We do know that some people have a harder time managing diabetes, but we don't know why. There is no evidence (yet!) that reducing exposures/increasing elimination of contaminants could help in diabetes management, but the possibility exists. It might be worth a try. Again, let me know if you try it, and whether or not it worked for you.
There have not yet been any successful intervention trials shown to prevent type 1 diabetes (although one trial has been shown to reduce the risk of developing type 1 related autoantibodies in children genetically at risk-- using hydrolyzed infant formula instead of regular formula-- see the list below). But, if you have type 1 diabetes in your family, and/or are interested in reducing the risk of your children developing the disease, studies do suggest a number of possible steps to try. None is guaranteed to work, of course, but these recommendations are not likely to lead to any harm either. See the linked pages for more information and sources. You could try to:
Please keep in mind that even if all these measures really do help and reduce the risk for our loved ones getting type 1 diabetes, many people still may get the disease. My younger son, who has type 1 diabetes, is living proof (although I didn't try them all!). Of course, the point is not to make anyone feel guilty; I could feel guilty about being vitamin D deficient, not supplementing with omega 3s or vitamin D, and possibly even eating bacon while conceiving a baby... but that's a waste of my time.
Timing may be critical, in that these factors may be most important during gestation, in infancy, or early childhood. If you are interested in reducing the risk of type 1 diabetes in a ten year old, like I am, then it may already be too late. Also bear in mind that diabetes has been around since ancient times, and will probably never be prevented entirely. That said, it used to be a rare disease.
There are a number of on-going, prospective studies of type 1 diabetes taking place now that follow people over time, and keep track of various environmental exposures before diagnosis. These studies are important in that they can help determine what factors can contribute to the development of disease. The Environmental Determinants of Diabetes in the Young (TEDDY) is one such study (TEDDY Study Group 2008). TEDDY includes measurements of many of the other environmental factors discussed in these pages, such as dietary factors, viruses, vaccines, and stress. Yet, like most other prospective studies, it does not include measurements of many of the environmental contaminant exposures discussed on this webpage (with some exceptions). Since the search for the cause of the rising rates of type 1 diabetes has thus far largely been fruitless, research into the possible involvement of multiple environmental contaminants in the development of the disease is in order. This research should entail:
We should focus research on those contaminants that humans are exposed to, especially in utero, via breastmilk, in food, or in consumer goods, and those that show effects in the laboratory that might be important in the development of type 1 diabetes. Many of the these contaminants have already been identified, but that does not rule out the possibility of additional substances as yet unstudied. Contaminants in combination with each other, or with other environmental factors may also be critical. Those that can disrupt the endocrine system and the development and function of the immune system deserve special focus.
Elucidating the role of contaminants may be complex. Effects are likely to depend on the dose, timing, gender, and other factors. Contaminants may act via a variety of mechanisms; the evidence of exposure may be long gone by the time the disease develops; contaminants may act in combination with other factors such as diet or lifestyle (or other contaminants) to influence the progression of disease; the effects of exposure may in part depend on an individual's genetic susceptibility; and cumulative exposures over the duration of life, beginning in utero (or even earlier?), may be important.
Unfortunately, one of the main animals used to study autoimmune diabetes in the lab, NOD (non-obese diabetic) mice, may not be appropriate to use to examine the effects of environmental contaminants on type 1 diabetes in humans (see the of mice and men page).
Another complication, which should give anyone the shivers, is the possibility that contaminants can have effects that can be passed down from one generation to the next. Children today may be showing health outcomes from exposures their parents or grandparents had. The implications of this possibility are frightening, but cannot be ruled out (see the gene expression and endocrine disruption pages for some examples and more information).
As it now stands, safety data for chemicals has relied on exposures to adults to predict the effects of individual chemicals on the immune system. Yet for many substances, these adult exposures are not the same as an exposure in utero, in infancy, or in early childhood, particularly because the immune system is developing during these times. Considering how many environmental contaminants can affect the developing immune system, it is likely that they could be involved in the development of autoimmune disease later in life. Safety evaluations should consider exposures during the developmental period, not only during adulthood (Dietert and Piepenbrink 2006) (see the autoimmunity page).
It's not just type 1 diabetes that is a concern. Up to 25% of children in some developed countries suffer from an immune-based disease. And yet, only a few existing chemicals have been tested for how they may affect the developing immune system (Dietert 2010).
Here is what some researchers say about the need to protect health by reducing contaminant exposures: "All of this evidence should encourage regulatory agencies to apply the precautionary principle and thus ban and/or substitute those chemicals that are likely to be harmful to the normal development of humans and wildlife" (Vandenberg et al. 2009).... "We are likely to witness dramatic improvements in human health, and reductions in medical costs, if environmental pollution is decreased" (Edwards and Myers 2007).
According to my U.S. Senator, Kirsten Gillibrand, the Environmental Protection Agency (EPA) has the authority to regulate more than 80,000 existing chemicals, yet has only had the resources to restrict the production of 5 chemicals over the past 30+ years. Efforts to reform the U.S. Toxic Substances Control Act are now underway and sorely needed.
Indeed, preventing pollution may be the most important action we can take. Like drugs, contaminants should be "presumed guilty until proven innocent," or shown to be safe before they are used. Scientists are not allowed to experiment on children in the lab; why should children be exposed to chemicals such that they are effectively experimental subjects in the real world?
If exposure to environmental contaminants is ultimately found to contribute to the development of type 1 diabetes, then this disease may in part be preventable.
A number of researchers have been kind enough to look at and comment on this website. Here are some of their comments.
Type 1 diabetes researchers have said:
Type 2 diabetes researchers have said:
Toxicologists have said:
If you are interested in staying up to date about the issues raised on this website, please visit the get involved page.