WASHINGTON — Licensed pesticide applicators who used chlorinated pesticides on more than 100 days in their lifetime were at greater risk of diabetes, according to researchers from the National Institutes of Health.
The associations between specific pesticides and incident diabetes ranged from a 20 percent to a 200 percent increase in risk, said the scientists with the institute’s National Institute of Environmental Health Sciences and the National Cancer Institute.
“The results suggest that pesticides may be a contributing factor for diabetes along with known risk factors such as obesity, lack of exercise and having a family history of diabetes,” said Dale Sandler, chief of the epidemiology branch at the National Institute of Environmental Health Sciences and co-author on the paper.
“Although the amount of diabetes explained by pesticides is small, these new findings may extend beyond the pesticide applicators in the study,” Sandler said.
Some of the pesticides used by these workers are used by the general population, though the strength and formulation may vary. Other insecticides in this study are no longer available on the market, but these chemicals persist in the environment and measurable levels may still be detectable in the general population and in food products.
For example, chlordane, which was used to treat homes for termites, has not been used since 1988, but can remain in treated homes for many decades. More than half of those studied in the National Health and Nutrition Examination Survey in 1999-2002, had measurable evidence of chlordane exposure.
“This is not cause for alarm,” added Sandler “since there is no evidence of health effects at such very low levels of exposure.”
Overall, pesticide applicators in the highest category of lifetime days of use of any pesticide had a small increase in risk for diabetes (17 percent) compared with those in the lowest pesticide use category. New cases of diabetes were reported by 3.4 percent of those in the lowest pesticide use category compared with 4.6 percent of those in the highest category.
Risks were greater when users of specific pesticides were compared with applicators who never applied that chemical.
For example, the strongest relationship was found for a chemical called trichlorfon, with an 85 percent increase in risk for frequent and infrequent users and nearly a 250 percent increase for those who used it more than 10 times.
In this group, 8.5 percent reported a new diagnosis of diabetes compared with 3.4 percent of those who never used this chemical.
Previous cross-sectional studies have used serum samples to show an association between diabetes and some pesticides. Diabetes occurs when the body fails to produce enough insulin to regulate blood sugar levels or when tissues stop responding to insulin.
Nearly 21 million Americans have diabetes. The cause of diabetes continues to be a mystery, although genetics and environmental factors such as obesity and lack of exercise appear to play roles.
To conduct the study, the researchers analyzed data from more than 30,000 licensed pesticide applicators participating in the Agricultural Health Study, a prospective study following the health history of thousands of pesticide applicators and their spouses in North Carolina and Iowa.
Among the 50 different pesticides the researchers looked at, they found seven specific pesticides — aldrin, chlordane, heptachlor, dichlorvos, trichlorfon, alachlor and cynazine — increased the likelihood of diabetes among study participants who had ever been exposed to any of these pesticides, and an even greater risk as cumulative days of lifetime exposure increased.
All seven pesticides are chlorinated compounds, including two herbicides, three organochlorine insecticides and two organophosphate pesticides.
“The fact that all seven of these pesticides are chlorinated provides us with an important clue for further research,” said Kamel.