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Insecticides May Increase Rheumatoid Arthritis Risk

Posted Nov 07 2009 10:01pm

A new study indicates that women who frequently used insecticides in their homes over a period of years may have increased their risk for autoimmune diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus.

According to the research, women who sprayed insecticides at least six times a year had double the risk of developing autoimmune disease compared to women who didn’t use insecticides.

In addition, the study led by Christine G. Parks, PhD, an epidemiologist with the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, found almost the same risk of autoimmune disease among women from environments with long-term insecticide spraying by commercial companies.

“We also saw that long-term application of insecticides by others in the home or in the lawn or garden about doubled disease risk,” she said.

The researchers studied the records of 76,861 postmenopausal and mostly white women between the ages of 50-79 who were enrolled in the Women’s Health Initiative Observational Study. Parks and associates focused on questions relating to farm history and insecticide use.

Of the women whose records were examined, 178 were eventually diagnosed with rheumatoid arthritis and 28 with lupus. There were seven other women who were diagnosed with both lupus and rheumatoid arthritis.

Parks said investigators found that a history of just working or living on a farm — although relatively frequent among the women in the survey — did not appear to increase risk of rheumatoid arthritis or lupus.
But compared to people who had never used insecticides, women who had personally mixed or applied insecticides regularly had double the risk of a rheumatic disease.

“About 46% of the rheumatoid arthritis cases occurred among women who mixed or applied insecticides themselves,” Parks said.
Parks cited studies showing that up to 75% of U.S. households use insecticides in the home or garden, with 20% of householders reporting that they had applied insecticide in the month before being surveyed. She also noted that insecticides don’t break down readily in the home environment.

“Our results also provide support for the idea that environmental factors may increase susceptibility or trigger the development of autoimmune diseases in some individuals,” said Parks. “We need to start thinking about what chemicals or other factors related to insecticide use could explain these findings.”

The researchers did indicate that there were some limitations to the study because the questions asked about insecticides did not address specific products.

“It is important to note that these are still relatively uncommon diseases affecting only a small percentage of adults, but I believe it provides proof of principle that these environmental exposures may be risk factors that need to be studied more thoroughly,” she said.

“Although our findings are not proof of a causal relationship with products currently on the market and available for household use,” Parks said, “I think the take-home message is that people should always follow recommended practices to reduce their individual exposures.”

The research was presented at the American College of Rheumatology’s annual meeting.

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