Secondhand smoke exposure in both childhood and adulthood is associated with an increased risk of rheumatoid arthritis in women, according to a study presented at the annual European Congress of Rheumatology.
“These results suggest that smoking by-products, whether actively or passively inhaled or absorbed, could generate autoimmunity, at least towards antigens involved in rheumatoid arthritis pathogenesis,” said Yann Nguyen, MD, MPH, of the center for research in epidemiology and population health at the University of Paris-Saclay in Villejuif and of Beaujon Hospital at the University of Paris in Clichy, France.
Dr. Yann Nguyen
Previous research has already repeatedly implicated smoking as a risk factor for rheumatoid arthritis positive for anticitrullinated protein antibodies (ACPA), especially in those who have the HLA-DRB1-shared epitope (SE) alleles, Dr. Nguyen explained to attendees. This study looked at whether exposure to others’ smoke had any similar associations.
The researchers relied on the French prospective cohort study known as E3N-EPIC (Etude Epidémiologique auprès de femmes de la Mutuelle Générale de l’Education Nationale), which is designed to examine potential associations between environmental factors and chronic disease. Of the 98,995 healthy French women the longitudinal study has tracked since 1990, this study included 79,806 participants with an average age of 49 years. A total of 698 women developed rheumatoid arthritis during the study an average of 11.7 years after baseline.
Exposure to secondhand smoke, or passive smoking, in childhood was defined as spending several hours a day in a smoky room as a child, based on participants’ self-report. Adult exposure to passive smoking referred to women’s self-report of spending at least 1 hour a day around actively smoking adults. Researchers further stratified participants according to whether they currently smoke, have never smoked, or used to smoke. Additional covariates in the fully adjusted models included body mass index and educational level.
About one in seven of the women (13.5%) reported exposure to childhood passive smoking, and just over half (53.6%) reported passive smoking exposure as adults. Overall, 58.9% of participants had secondhand exposure in adulthood or childhood, and 8.25% had both.
A positive association existed between childhood exposure and rheumatoid arthritis in the unadjusted and adjusted models. In the fully adjusted model, the risk of rheumatoid arthritis was 1.24 times greater overall for those exposed to secondhand smoke in childhood compared with those who had no exposure. The risk was even greater, however, among women who had never smoked (hazard ratio, 1.42), and the association was not statistically significant in women who had ever smoked.
Similarly, risk of rheumatoid arthritis was greater among those women reporting exposure to passive smoking in adulthood in the unadjusted and adjusted models (HR, 1.19 after adjustment). Once again, women who had never smoked had a modestly higher increased risk (HR, 1.27) if they had secondhand smoke exposure in adulthood, but no statistically significant association existed for women who were current or former smokers.
Dr. Loreto Carmona
Although research had previously shown the association between active smoking and rheumatoid arthritis, these new findings suggest clinicians need to emphasize to their patients this additional negative effect from smoking.
Dr. Hendrik Schulze-Koops
Dr. Nguyen, Dr. Carmona, and Dr. Schulze-Koops have reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.