Lead author and associate professor at the University of California, Davis, Department of Environmental Toxicology, Michele La Merrill, PhD, and colleagues explored the continued use of persistent organic pollutants (POPs) and resultant exposure in individuals living in countries such as those in South Asia in an article published in November 2019 in Environmental Science & Technology. These countries have not complied with the 2004 United Nations Stockholm Convention ban on these POPs and have continued to produce and use POPs, including DDT and polychlorinated biphenyls (PCBs).

Dr. La Merrill noted, “Our findings evoke a new interpretation of Rachel Carson’s famous book Silent Spring, in that the high DDT exposures of South Asian immigrants in the U.S. currently fall on deaf ears in the U.S.,” adding, “Although DDT remains in use in other nations and migration globalizes these exposures, people in the U.S. often mistakenly regard DDT exposure as no longer relevant to our society due to its ban in this country nearly 50 years ago.”

Funded by the National Institutes of Health and the USDA National Institute of Food and Agriculture, the team studied 30 pollutants identified in plasma samples from 147 subjects and found that plasma levels of DDT were independently associated with both body mass index (BMI) and waist circumference. Additionally, DDT was associated with insulin insensitivity (P = .001); increased adiposity (increases of 1.26 kg/m2 BMI and 3.58 cm waist circumference, P <.0001); as and increased rates of obesity (OR = 2.17, P <.001, BMI-based; OR = 2.37, P = .001, waist-based); prediabetes (OR = 1.55, P = .02); and diabetes (OR = 1.72, P = .01), when multivariable models that addressed potential confounders such as age, sex, years in the U.S., education, and fish protein consumed were used.

While it is known that Asian Indian ancestry is associated with increased risk, the impact of immigrants from these regions bringing this inherent medical likelihood to their destination country has not been adequately recognized. Dr. La Merrill noted that healthcare providers may not be familiar with this additional risk and, as a result, may not intervene sufficiently and early enough. 

Although more research is needed, the scientists concluded that their findings might not only help explain the increased diabetes risk for Indian immigrants, but also improve public-health strategies to screen and treat the roughly 1.8 billion South Asians throughout the world who are at higher risk.

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