Previous exposure to pollutants may contribute to the higher risk of metabolic disorders among Asian Indian immigrants to the US, researchers have found.
Writing in the journal Environmental Science & Technology, they link particularly high levels of dichlorodiphenyltrichloroethane (DDT) with increased risk of diabetes.
A team led by Michele A La Merrill from the University of California found that immigrants with higher levels of DDT in their blood were more likely to be obese compared to people with lower levels of DDT.
Since high DDT levels were associated with obesity, the researchers hypothesised that DDT may also increase the risk of nonalcoholic fatty liver disease in humans.
DDT and other persistent organic pollutants (POPs) accumulate in human fat tissues and stay there for months or years. Although DDT has been banned in developed countries, some South Asian countries continue to produce and use it.
This led La Merrill and colleagues to wonder whether prior exposure to POPs could influence Asian Indians’ diabetes risk, even after they moved to the US.
Based on results from animal studies, they hypothesised that POPs could possibly contribute to diabetes by triggering excess fat deposition in the liver. DDT, they say, possibly primes the liver to be susceptible to fat accumulation. Rodent studies have revealed that this pollutant increase liver fat and induce fatty liver.
To test their hypothesis, they measured 30 environmental pollutants in blood samples of 147 South Asian immigrants living in the US. They also measured the fat accumulation in their liver and spleen.
They detected that the levels of POPs were much higher than the levels previously found in other populations in the US. They found a positive association between DDT and insulin levels in the immigrants.
This is consistent with experimental evidence that DDT exposure caused increased circulating insulin in adult mice, they write. Increased insulin means insulin resistance when cells in muscles, body fat and liver start resisting or ignoring the signal of insulin, shooting blood glucose levels.
Biplab Das is a science writer based in Bangalore, India.
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