Secondhand smoking exposure in childhood poses risk of adult-onset RA

Children whose parents smoke are likely to develop seropositive rheumatoid arthritis (RA) as adults, regardless of their smoking habits, a study suggests.

The study used data from the Nurses’ Health Study II prospective cohort, which included 90,923 women who completed biennial questionnaires. Researchers evaluated the effect of (1) maternal smoking during pregnancy (in utero exposure), (2) childhood parental smoking, and (3) years lived with smokers since age 18 years.

Over a median follow up of 27.7 years, a total of 532 incident RA cases (66 percent seropositive) were documented. Cox proportional hazards regression analysis adjusted for confounders showed that maternal smoking during pregnancy contributed to an increased risk of RA (hazard ratio [HR], 1.25, 95 percent confidence interval [CI], 1.03–1.52). However, this association disappeared after controlling for subsequent smoking exposures.

Likewise, childhood parental smoking was associated with seropositive RA (HR, 1.41, 95 percent CI, 1.08–1.83). Controlled direct effect analyses confirmed the relationship between childhood parental smoking and seropositive RA (HR, 1.75, 95 percent CI, 1.03–2.98) after controlling for adult personal smoking, which was pronounced among ever smokers (HR, 2.18, 95 percent CI, 1.23–3.88).

There was no significant association observed between adult passive smoking and RA (20+ years lived with a smoker vs none: HR, 1.30, 95 percent CI, 0.97–1.74).