Passive smoking in childhood increases the risk of developing rheumatoid arthritis

To investigate the link between smoking status, including childhood and adult passive exposure, and the risk of incident RA.

The French E3N cohort includes 98 995 female volunteers prospectively followed since 1990. Self-administered questionnaires sent every 2-3 years collected medical events, general, lifestyle and environmental characteristics. RA diagnoses were collected in three successive questionnaires and confirmed if women received reimbursement for an RA-specific medication. The risk of incident RA was estimated using an age-adjusted Cox model that considers smoking status as a time-dependent variable.

Among 71 248 women, 371 incident RA cases were confirmed. Ever-smokers not exposed to passive smoking had an increased risk of RA [1.38 (95% CI 1.10, 1.74)]. In never-smokers, passive smoking exposure during childhood was associated with a borderline increased risk of RA in the same range as active smoking in adults, with an hazard ratio (HR) of 1.43 (95% CI 0.97, 2.11). Ever-smokers who also had childhood passive smoking exposure had a higher risk of RA than smokers not exposed during childhood [HR 1.67 (95% CI 1.17, 2.39)], but without a significant difference (P = 0.30). RA began earlier in smokers exposed to childhood passive smoking.

This study confirms that active smoking is associated with an increased risk of RA. It suggests for the first time that passive exposure to tobacco during childhood might also increase the risk of RA in future light smokers and probably non-smokers. Our results highlight the importance of avoiding any tobacco environment in children, especially in those with a family history of RA.