Bug Spray Linked to RA, Lupus

October 29, 2009

by Janis C. Kelly

PHILADELPHIA, Pennsylvania—Household bug spray, not just agricultural pesticides, may increase women's risk for both rheumatoid arthritis (RA) and systemic lupus erythematosus (lupus, SLE), according to research presented at the American College of Rheumatology 2009 meeting.

{}”Insecticide exposure may increase risk of autoimmune rheumatic diseases (ARD) in post-menopausal women,” said lead investigator Christine G. Parks, PhD, who is in the Epidemiology Branch of the National Institute of Environmental Health Science, Research Triangle Park, NC.

RA, SLE risk increase with frequency of insecticide application

Using data from the Women's Health Initiative Observational Study, the investigators found that, compared with non-use:

• Personal insecticide use (mixing or applying) doubled autoimmune rheumatic disease (ARD) risk
• Applying insecticides 6 or more times per year increased risk 4-fold
• Having applied household insecticides for 20 or more years tripled ARD risk
• Commercial residential insecticide exposure was significantly associated with ARD risk regardless of farming history (age-adjusted HR=1.85; 95% CI 1.13, 3.04 for ≥20 years)

Dr. Parks reported that increasing cumulative insecticide use (years X applications) also showed a significant trend of association (p=0.0004) with ARD risk, and that these associations persisted after adjusting for farming and covariates.

The data also confirmed other studies that linked having lived or worked on a farm with ARD risk, but the effect size was diminished after adjusting for covariates and insecticide use.

The researchers analyzed data from 76,861 women, aged 50-79 years. They examined self-reported lifetime personal or commercial residential insecticide use and having lived or worked on a farm in relation to risk of incident ARD, confirmed by use of disease modifying anti-rheumatic drugs at year 3 of follow-up.

The dataset included 213 women with new-onset disease, including 178 with RA only, 27 with SLE only, and 8 with both RA and SLE.

“Despite the small number of SLE cases, disease-stratified analyses indicated similar associations as seen for RA,” Dr. Parks said.

Translating research into practice: time to consider insecticide as an environmental trigger?

The analysis showed that, when compared to people who had never used insecticides, those who had personally mixed or applied insecticides were at greater risk of developing a rheumatic disease, with more than double the risk in those women reporting more frequent or longer duration of use.

“Although suggestive, we need to start thinking about what chemicals or other factors related to insecticide use could explain these findings,” says Christine G. Parks, PhD; epidemiologist, National Institute of Environmental Health Sciences, National Institutes of Health, Bethesda, MD, and the lead investigator in the study. “Our results also provide support for the idea that environmental factors may increase susceptibility or trigger the development of autoimmune diseases in some individuals.”

Reference

1. Parks CG. Farm History, Insecticide Use and Risk of Autoimmune Rheumatic Disease in the Women's Health Initiative Observational Study. Presented at the American College of Rheumatology 2009 meeting, Philadelphia, October 18, 2009. Presentation Number: 614.