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Study Links Heptachlor, PCBs and Form of Vitamin E to Diabetes

(Beyond Pesticides, May 25, 2010) An analysis of 266 potential environmental contributors to type 2 diabetes published May 20, 2010 in the online edition of the journal PLoS ONE, links the disease to individuals who have higher levels of polychlorinated biphenyls (PCBs) and the pesticide heptachlor, as well a form of vitamin E found at high levels in soybean and corn oil, in their bodies compared to the general population. PCB was banned in 1979 and most uses of heptachlor were canceled between 1978 and 1989 (except for limited control of fire ants, which continues), but the compounds persist in the environment, especially near former industrial sites or contaminated soil. Environmentalists point to the fact that chemicals banned decades ago are still increasing people’s risk of disease, as a reason to take a precautionary approach when evaluating and registering chemicals.

The analysis, led by Atul Butte, MD, PhD, assistant professor of medical informatics and pediatrics at the Stanford University School of Medicine, drew on data collected by the Centers for Disease Control and Prevention as part of the National Health and Nutrition Examination Survey (NHANES) to examine a wide range of environmental influences on type 2 diabetes. Dr. Butte conceived of an “environment-wide association study,” a parallel to genome-wide association studies that have become a tool of choice among geneticists in recent years. The time has come to put an equal focus on environmental risk factors, says Dr. Butte. “Genetics is certainly a hot field, but so far genome-wide association studies have not explained a large amount of the risk for type 2 diabetes and other diseases,” he says. “So we decided to borrow the concept of the genome-wide association study and apply it to the environment.”

The researchers used NHANES data from 1999 to 2006. Each cohort included between 507 and 3,318 people who had their blood and urine tested. Dr. Butte divided these participants into a “case” group, who had high concentrations of blood sugar (surrogate marker for diabetes), and a “control” group, who had normal blood sugar. The analysis confirmed previous findings that high blood levels of PCBs were highly associated with the disease. The prevalence of Type 2 diabetes was two to three times higher for those with the higher levels of the pollutant compared to those with the lowest. Type 2 diabetes prevalence among those with high levels of heptachlor epoxide, a break down product of heptachlor, was at about two times higher than those with low levels of the compound.

Heptachlor was first registered in the United States in 1952 for in agriculture, as well as home and garden insect control, for termite control and as a seed treatment. Heptachlor and its metabolite, heptachlor epoxide, had been demonstrated to cause cancer and birth defects in laboratory mice and rats. They also were known to persist in soil for many years, and to bioaccumulate throughout the food chain. Most uses of heptachlor were cancelled in March 1978, but existing stocks were allowed used by pineapple growers for years following the cancelation. In 1989, all heptachlor tolerances (residue limits in foods) were revoked and replaced with action levels (limits set for unavoidable residues in foods resulting from environmental contamination, which are lowered as actual residue levels decline).

The analysis also indentified a factor never before linked to type 2 diabetes, a form of vitamin E called gamma-tocopherol. Vitamin E appears in eight different molecular forms; gamma-tocopherol is the most common form in the American diet, and is particularly high in soybean and corn oil (see chart of tocopherol sources). Prevalence of type 2 diabetes among study participants with high blood levels of gamma-tocopherol—which, like other forms of vitamin E, is an antioxidant—was two times greater compared to people with low levels of the nutrient. Butte says that much additional research is needed to sort out how this form of vitamin E is related to type 2 diabetes.

There was also good news. The researchers confirmed previous studies showing the protective association of the vitamin beta-carotene. The prevalence of type 2 diabetes among people with high amounts of beta-carotene, a form of vitamin A, was about 40% lower than those with lowest amounts of the vitamin.

Type 2 diabetes affects around 23.6 million people in the United States, or 7.8% of the population, according to the American Diabetes Association. Its prevalence is rising so quickly that the Centers for Disease Control and Prevention (CDC) has labeled it an epidemic. The condition occurs when the body stops responding to insulin, which leads to high concentrations of blood sugar and, if not controlled, a host of health problems, including heart disease, blindness, kidney failure, and lower-extremity amputations.

Beyond Pesticides recommends reducing your risk to a number of environmentally-linked diseases by eating an organic diet, whenever possible. It’s healthier for your family, farm and farmworker families and the environment. Learn more at Beyond Pesticides’ Organic Food webpage.


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