PHILADELPHIA -- Women who frequently sprayed their homes with insecticides over a period of years may have put themselves at risk for autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus, a researcher said here.
Among women who sprayed at least six times a year, the risk of autoimmune disease was more than twice that of women who didn't use insecticides (HR 2.47, 95% CI 1.51 to 4.03, P=0.0036).
The results were similar among women who used insecticides for 20 years or more (HR 2.07, 95% CI 1.31 to 3.25), according to Christine G. Parks, PhD, an epidemiologist with the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina.
"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 told attendees at the American College of Rheumatology's annual meeting.
She found almost the same risk of autoimmune disease among women from environments with long-term insecticide spraying by commercial companies (HR 1.85, 95% CI 1.13 to 3.04).
The researchers examined records of 76,861 postmenopausal and predominantly white women ages 50-79 enrolled in the Women's Health Initiative Observational Study. Parks and colleagues focused on questions relating to farm history and insecticide use.
Of those whose records were reviewed, 178 later were eventually diagnosed with rheumatoid arthritis and 28 with lupus. An additional seven women 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.
The relationships held when the data were adjusted for farm history, age, race, ethnicity, education, occupation, smoking, and other risk factors for disease, she 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."
http://www.medpagetoday.com/Rheumatology/Arthritis/16572