A unique analysis, led by Atul Butte, assistant professor of medical informatics and pediatrics at the Stanford University School of Medicine, used a government database to examine 266 potential environmental contributors to type 2 diabetes and confirmed links between several pollutants and the disease that affects about 24 million Americans. The research appears online in the May 20th edition of PLoS One.
Butte and colleagues examined data collected by the Centers for Disease Control and Prevention as part of the National Health and Nutrition Examination Survey (NHANES). The participants in the survey answer questionnaires about their health and submit blood and urine samples every two years. The agency then tests each sample for hundreds of pollutants and nutrients and, if present, measures the concentration.
Using this data, the researchers identified three factors linked to high blood sugar levels, including polychlorinated biphenyls (PCB’s), heptachlor epoxide, and a form of vitamin E called gamma-tocopherol. A positive factor affecting blood glucose levels was beta-carotene; those with the highest levels had 40% lower prevalence of diabetes.
PCB’s are a group of man-made organic chemicals that were used in a variety of products such as industrial electrical, heat transfer, and hydraulic equipment. They can also be found in oil-based paint, plastics, and floor finish. They have been banned from use in the United States since 1979 but may still be present in some products and materials made before that time.
Heptachlor, a breakdown product of a previously common pesticide, was banned in 1988 however it persists in water and soil and can accumulate in the tissues of animals. The chemical is known to be able to be passed from mothers to infants through breast milk.
Vitamin E appears in eight different molecular forms: four tocopherols and four tocotrienols. While alpha-tocopherol is the main vitamin E source in dietary supplement products and preferentially absorbed by the human body, gamma tocopherol is the most common form in the standard American diet.
Beta-carotene is a precursor to vitamin A and found mainly in yellow- and orange-colored foods such as carrots, pumpkins, mangoes, and sweet potatoes. It is also found in dark, leafy greens such as spinach and kale.
The scientists are careful to caution, however, that an association doesn't necessarily mean cause, and that more research is needed to fully understand these complex relationships. Also, Butte considers his study a “first step” toward broader examinations of environmental influences on disease, because the analysis only examines a small number of factors.