Indian Americans who may have been exposed to high levels of DDT are likely to be at greater risk for developing diabetes, concluded researchers at the University of California, Davis, in a study published Nov. 20 in the American Chemical Society’s journal Environmental Science & Technology.
DDT, short for dichlorodiphenyltrichloroethane, is an insecticide that was commonly used in agriculture until its toxic side effects were exposed. In 2004, the United Nations Stockholm Convention banned the production and use of many persistent organic pollutants, or POPs, such as DDT and polychlorinated biphenyls, or PCBs.
However, POP production and use continue in some nations that did not ratify the treaty, including India and other South Asian countries. Previous studies have found DDT in samples taken from the environment, food and people of the Indian subcontinent, noted the researchers.
Based on results from animal studies, the researchers hypothesized that POPs could contribute to diabetes by causing excess fat deposition in the liver, which in turn can lead to insulin resistance.
After animal testing, the researchers turned to humans to test their hypothesis, and examined the levels of 30 environmental pollutants in blood plasma samples from 147 Indian American participants, 45 to 84 years old, living in the San Francisco Bay Area.
The researchers found that levels of numerous POPs that were much higher than levels previously found in other U.S. populations. The participants with higher levels of DDT in their blood were more likely to be obese, store excess fat in their livers and show increased insulin resistance compared to people with lower levels, according to the study.
Although more research is needed to establish a causal relationship, these findings could help explain the increased diabetes risk for Indian Americans and has public health implications for the approximately 1.8 billion South Asians throughout the world, the researchers said.
In India, more than 69 million people suffer from diabetes, according to a 2015 study published in the journal Endocrine News. That number is expected to grow exponentially as Indians adapt to Western diets.
“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.,” said lead author Michele La Merrill, an associate professor in the UC Davis Department of Environmental Toxicology.