Among the reasons to believe that the environment might be involved in diabetes, according to Carpenter, is that its prevalence varies across geographic areas, and people who move to places where it’s more common become more likely to get sick. Kahn, however, said that effect could be due to people migrating to more developed areas, where a richer diet and more sedentary lifestyle are the norm.
Further evidence came from a sweeping study of more than 2,000 adults, conducted by the U.S. Centers for Disease Control and Prevention, that found people with the highest levels of six pollutants were 38 times more likely to have diabetes than those with the lowest exposure. The chemicals, including PCBs, dioxins and DDE, were chosen because they were present in at least 80 percent of participants.
“That’s just mind-boggling,” Carpenter said.
Also, Vietnam veterans exposed to the dioxin-laced defoliant Agent Orange were significantly more likely than average to become diabetic, prompting the government to offer compensation to diabetic veterans.
The way the new Great Lakes study was conducted makes its findings especially convincing, according to the authors and other experts.
Other research has found similar links between diabetes and pollutants, but they were cross-sectional studies, which means “you measure the level of a chemical and ask people if they have diabetes,” Turyk said.
Those studies could easily be skewed, Turyk said, because they don’t indicate whether diabetes developed before a person was exposed to pollutants. But in the new paper, she and colleagues measured participants’ exposure to DDE from blood samples taken in the mid-1990s, then followed up with them for nearly a decade to see who among them became diabetic, thereby ensuring that diabetics were exposed before they were diagnosed.
The paper further bulwarked the claim by discrediting the hypothesis that the link between the two is a statistical fluke. Critics have suggested that pollutants like DDE only appear to be potential causes of the disease because diabetics more slowly break down the chemicals, and therefore carry more of them.
But Turyk, sharing principal research duties with Henry Anderson of the Wisconsin Division of Public Health and Victoria Persky at the University of Illinois-Chicago, quashed that theory by showing no difference in DDE metabolism rates between diabetics and non-diabetics.
“This paper clearly shows that’s not the case,” said Carpenter. “It’s a very important contribution because of that fact.”
The researchers controlled for obesity, age and other risk factors, and still found a link to DDE exposure. The study didn’t distinguish between Type 2 and Type 1, or early-onset diabetes, but most diabetics in the study suffered from Type 2, which is more common in adults.
The authors said the relatively small number of participants and short duration limit the reliability of the findings. In addition, the link to DDE was relatively weak compared with past research.
Like nearly all human health research, it doesn’t directly show that chemicals in the environment cause diabetes.
“With epidemiology, you gather a body of evidence against something,” she said. “You can never really prove something causes something else.”
Scientists still don’t understand the mechanism by which DDE and other chemicals might contribute to diabetes, according to Carpenter, though he said pollution seems to disrupt the way genes produce proteins and “basically change the biochemistry of the cell.”
“It may be that they’re toxic to the pancreas,” which produces insulin Kahn added. “We don’t know.”
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6 Comments
Add CommentIt may be that theyre toxic to the pancreas, which produces insulin Kahn added. We dont know.
Reply | Report Abuse | Link to thisWhy not test for a correlation between DDE and insulin resistance, which is usually the first step toward adult-onset type 2 diabetes? This would be an easy way to figure out if DDE is hurting pancreas function or if it's more of a glucose receptor issue.
Data on insulin resistance was not available for the Great Lakes charter boat captains. Insulin resistance in non-diabetics was examined in the large CDC study, called NHANES, mentioned in the story (Lee et al, Diabetes 30:628, 2007). These authors found that insulin resistance was associated with organochlorine pesticides, but not PCBs or dioxins.
Reply | Report Abuse | Link to thisIt is perhaps more likely that insulin resistance and other factors preceding a diagnosis of diabetes may cause abdominal obesity than the other way around.
Reply | Report Abuse | Link to thisThe primary disability of the Veterans from Northeast Cape, Alaska is Diabetes and Heart Failure. NE Cape is a Super Fund Site and heavily polluted with PCB's.
Reply | Report Abuse | Link to thisOf the 2,500 or so vets, diabetes is endemic. Cancer and heart attacks are common.
But, the Russians never took the station! (not that they ever wanted it).
I've just returned from St. Lawrence Island where we are studying diseases in the Siberian Yupiks who live there. They have extremely elevated levels of PCBs, and those families with hunting camps at the Northeast Cape have higher levels than those that do not. PCBs cause diabetes and heart disease. Where can I find the evidence for these diseases are elevated in Veterans who worked there?
Reply | Report Abuse | Link to thisI've made a website summarizing the studies on contaminants and diabetes: www.diabetesandcontaminants.org. It focuses on type 1, but I also included studies on type 2 and gestational diabetes, since there is overlap among these diseases. And, I included studies on contaminants and insulin resistance, metabolic syndrome, and other pre-diabetes conditions.
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