Secondhand smoke may up risk of RA

Exposure to secondhand smoke, regardless of whether it is during childhood or adulthood, is associated with an increased risk of developing rheumatoid arthritis (RA) among women — particularly in those who never smoke themselves, according to data from the E3N-EPIC study presented at the EULAR 2021 Congress.

While active smoking is an established risk factor for developing RA, less is known about the effect of passive smoking through secondhand smoke exposure. 

“To date, active smoking has been the most reproducibly reported risk factor for anti-citrullinated protein antibodies positive RA, particularly [in] persons who carry the HLADRB1-shared epitope alleles,” explained presenting author Dr Yann Nguyen from the University of Paris-Saclay in Villejuif, France.

To examine the relationship between passive smoking and RA risk, Nguyen and colleagues analysed data of 79,806 healthy French women (mean age 49 years) who participated in the large prospective E3N-EPIC cohort. RA cases were identified using specific questionnaires and medication reimbursement database. [EULAR 2021, abstract OP0012]

Exposure to passive smoking referred to having been in a smoky room for several hours a day during childhood or for ≥1 hour a day during adulthood. Of the entire cohort, 10,810 (13.5 percent) had been exposed to passive smoking during childhood, and 42,807 (53.6 percent) had been exposed as adults.

Over a mean follow-up of 11.7 years, 698 women in the overall population had developed RA.

In the overall population, individuals exposed to passive smoking during childhood had a 24 percent increased risk of RA compared with those not exposed (adjusted hazard ratio [HR], 1.24, 95 percent confidence interval [CI], 1.01–1.51).

When the participant smoking status was taken into account, RA risk was increased only in women who never smoked (HR, 1.42, 95 percent CI, 1.07–1.88), but not in those who have smoked themselves (HR, 1.10, 95 percent CI, 0.83–1.46).

Similarly, exposure to secondhand smoke during adulthood was also associated with increased RA risk in the overall population (HR, 1.19, 95 percent CI, 1.02–1.40). Again, when the analysis was stratified by individual smoking status, the increased risk was only seen in women who had never smoked (HR, 1.27, 95 percent CI, 1.02–1.57), but not in those who had ever smoked themselves (HR, 1.16, 95 percent CI, 0.93–1.44).

In addition, passive smoking during childhood was associated with earlier onset of RA, especially in those who also smoked themselves (p=0.0015).

“In this large prospective cohort, passive smoking in childhood or adulthood was associated with an increased risk of RA. Moreover, RA may occur earlier with passive smoking exposure during childhood,” Nguyen concluded.

“Such exposure should be limited as much as possible, especially in subjects at risk of RA, to prevent the onset of the disease,” he urged.

On the other hand, doctors also have a role in informing their patients on the risk of RA with exposure to secondhand smoke, even in childhood.

“These results suggest that smoking by-products, whether actively or passively inhaled absorbed … could favour citrullination in genetically proned subjects, years before the first symptoms,” said Nguyen.