Passive smoking associated with an increased risk of RA

Exposure to passive smoking in childhood and/or adulthood is associated with an increased risk of rheumatoid arthritis (RA). This was found in the large prospective E3N-EPIC cohort study of French women. The effect is more pronounced in women who have also actively smoked during their lives. Furthermore, passive smoking during childhood could lead to an earlier onset of RA [1].

Active smoking is an established risk factor for RA [2]. The role of passive smoking in the development of RA has not been studied thoroughly. The E3N-EPIC cohort study focuses on diet and hormones as major components of women’s health and the team performs analytical epidemiological research with interests in environment. The current analysis of E3N-EPIC was presented by Dr Yann Nguyen (Université Paris-Saclay, France) and aimed to fill this gap in the literature. The study included 79,806 women (mean age at baseline 49.0); 698 incident RA cases have been identified since the initiation of the project in 1990. At baseline, participants were asked whether they were exposed to passive smoking in their childhood or adulthood. A cox proportional hazards model was used to analyse the data. The adjusted model controlled for active smoking, passive smoking exposure in childhood or adulthood, educational level, and baseline BMI. Data was stratified on active smoking status (ever-smoker or never-smoker).

Passive smoking in childhood (non-cases 13.5% vs RA cases 16.3%; HR 1.24; 95% CI 1.01–1.51) and adulthood (non-cases 53.6% vs RA 57.45%; HR 1.19; 95% CI 1.02–1.40) were significantly associated with an increased risk of RA. Among the participants exposed to passive smoking, the effect was larger for ever-smokers compared with never-smokers (absolute risk 53.67/100,000 vs 47.59/100,000 per year). Both these subgroups had an increased risk of RA compared with never-smokers with no exposure to passive smoking: being a never-smoker with exposure to passive smoking had an HR 1.33 (95% CI 1.08–1.6), ever-smoker plus exposure to passive smoking had an HR 1.50 (95% CI 1.22–1.84).

Participants who were not exposed to passive smoking and never smoked had a later age of disease onset (mean age 66.5) compared with participants who were exposed to passive smoking (mean age 63.7), had actively smoked (mean age 63.4), or had been exposed to passive smoking and had actively smoked (mean age 62.3). In addition, in the subgroup of the childhood passive smoking, ever-smokers had an earlier age of RA onset than never-smokers (mean age 60.6 vs 64.2). Dr Nguyen summarised the findings by saying that exposure to passive smoking in childhood and/or adulthood is associated with an increased risk of RA, and that passive smoking in childhood could lead to an earlier age of RA onset. He suggested that the results could be explained by a citrullination effect of passive smoking in genetically predisposed individuals.

1. Nguyen Y, et al. Association between passive smoking in childhood and adulthood and rheumatoid arthritis: results from the French E3N-EPIC cohort study. OP0010, EULAR 2021 Virtual Congress, 2–5 June.
2. Di Giuseppe D, et al. Arthritis Res Ther. 2014;16(2):R61.

 

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Posted on 2 August 20213 August 2021