with Obesity to Raise Diabetes Risk
by Emerging Health Threats Forum   
Exposure to dioxins is linked to insulin resistance, which causes diabetes, according to research published this month in Epidemiology.1 Experts say that there is now strong evidence for a link between diabetes and exposure to persistent organic pollutants (POPs), including dioxins, but that this is still being largely overlooked by the medical community.

“There’s just been a flood of evidence linking POPs to diabetics in the last five years,” says David Carpenter, Director of the Institute for Health and the Environment at the University at Albany, New York, USA. “When you put this study in the context of what’s being done in other groups, it gives a very convincing story.”

The researchers, led by Jung-Wei Chang of the National Cheng Kung University in Tainan, Taiwan, measured the levels of serum dioxins, fasting glucose, and insulin in 1234 people living near an abandoned pentachlorophenol manufacturing plant. They used a homeostasis model, which uses fasting glucose and insulin levels to estimate insulin resistance. After controlling for risk factors such as age, obesity, and family history of diabetes, they found a positive association, with a linear dose-response, between serum dioxins and the prevalence of insulin resistance.

Earlier studies have linked a variety of POPs, including dioxins, polychlorinated biphenols (PCBs) and organochlorine pesticides such as DDT, to an increased risk of type II diabetes. Since obesity is linked with greater levels of POPs in the body, scientists speculate that the link between obesity and the development of diabetes might be mediated through these toxins.

“People get obese because they eat too much animal fat, and that’s where the contaminants are,” Carpenter points out. This effect may explain why indigenous populations in Canada are at higher risk of diabetes, Carpenter explains, as they are often exposed to greater levels of POPs than the general population.

One study in particular,2 led by Duk-Hee Lee of the Kyungpook National University in Daegu, Korea, looked at 2016 participants to the 1999–2002 National Health and Nutrition Examination Survey, which took blood samples from a cross section of the general US population, and found no association between obesity and diabetes among people with no detectable levels of POPs in their blood. This implies that the risk of diabetes from obesity could be largely due to POPs, which accumulate in adipose tissue, rather than physiological changes that come with obesity, Carpenter says.

“I am somewhat sceptical of that finding,” says David Jacobs, Professor of Public Health at the University of Minnesota and one of Lee’s co-authors. The association between exposure to POPs and diabetes is stronger in obese people, he points out. But it’s clear that POPs and obesity interact to raise the risk of diabetes, he says.

This would suggest that losing weight may only partially reduce the risk for diabetes. POPs accumulate in adipose tissue — which means that weight loss releases the toxins back into the blood. “That stuff has got to go somewhere,” Jacobs says. “It’s clear that POPs [released from fat deposits] distribute into blood and other tissues.”

Worryingly, some data show a stronger association with diabetes at low concentrations of POPs, Jacobs says. “We have seen that kind of pattern, but it’s very difficult to interpret,” says Jacobs. Because of the difficulty of measuring low-level exposure to these pollutants, a lot more research is needed to confirm whether they have this effect, he argues.

Despite the body of evidence linking POPs and diabetes, the link is still not widely acknowledged in the medical community. “Physicians are totally oblivious to this being a risk factor,” Carpenter says. “The nutrition community have oversold the benefits of fish and underplayed the dangers of contaminants.”

Although production of many of the toxins studied has been banned worldwide, they persist in the environment, are distributed globally, and continue to bioaccumulate in the food chain. Pesticides like DDT, which are still used in malarial regions, can turn up in the food supply all over the world. And others are still on the increase. “[POP] exposure is to some degree going down, except in the case of flame retardants where exposure is increasing exponentially,” Carpenter says. Flame retardants are structurally very similar to PCBs, he points out, and so these too should be investigated for the potential to cause diabetes — especially as children are among the most highly exposed population groups.