MONDAY, Oct. 19 (HealthDay News) -- New research suggests a link between women's exposure to household insecticides -- including roach and mosquito killers -- and the autoimmune disorders rheumatoid arthritis and lupus.

The scientist did not find a direct cause-and-effect relationship between insecticide exposure and the illnesses, and it's possible that the women have something else in common that accounts for their higher risk. But epidemiologist Christine Parks, lead investigator of the study, said the findings do raise a red flag.

"It's hard to envision what other factors might explain this association," said Parks, an epidemiologist with the National Institute of Environmental Health Sciences who was to present the study over the weekend at the American College of Rheumatology annual meeting in Philadelphia.

Previous research has linked agricultural pesticides to higher risk of rheumatoid arthritis and lupus, two diseases in which the immune system goes haywire and begins to attack the body. Farmers, among others, appear to be vulnerable.

Parks and her colleagues wanted to find out whether smaller doses of insecticides, such as those people might encounter at home from either personal or commercial residential use, might have a similar effect.

The researchers examined data from a previous study of almost 77,000 postmenopausal women aged 50 to 79. Their findings were to be released Monday at the American College of Rheumatology's annual scientific meeting in Philadelphia.

Women who reported applying insecticides or mixing them -- about half -- had a higher risk of developing the two autoimmune disorders than women who reported no insecticide use. This was the case whether or not they had lived on a farm. Those who used or mixed the insecticides the most -- judged by frequency or duration -- had double the risk.

Even so, the risk of developing the diseases remained very low. Overall, Parks said, about 2 percent of older adults develop the conditions.

Parks said the insecticides that the women used included insect killers, such as those designed to eradicate ants, wasps, termites, mosquitoes and roaches. They didn't include insect repellents.

There are some caveats to the research. For one, it's not clear exactly what products the women used or when. "Over time, there have been major changes in what products were available for home use," Parks said.

And while researchers tried to take into account the influence of factors like age that may boost a woman's risk of getting autoimmune diseases, it's possible they missed something that boosted the risk of illness.

Could gardening, which often entails insecticide use, be a contributing factor? That's possible. But Parks said a lot of insecticide use takes place inside the home, not outside in the garden.

For now, she said, the findings indicate the need for "more research on environmental risk factors and better understanding of what factors might explain these findings, what chemicals might be associated with these risks."

She declined to speculate on how insecticides might cause problems in the body.

"I would recommend that people read the labels and take precautions to minimize their personal exposure" to insecticides, she said. "This is the case regardless of whether these results are implicating a chemical that's on the market now or was before."

More information

Learn more about insecticides from the National Institutes of Health.

SOURCES: Christine Parks, Ph.D., epidemiologist, National Institute of Environmental Health Sciences, Research Triangle Park, N.C.; Oct. 17, 2009, presentation, American College of Rheumatology annual meeting, Philadelphia

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