medwireNews: Researchers have investigated the association between passive exposure to tobacco smoke during childhood and the risk for rheumatoid arthritis (RA) later in life.
Marie-Christine Boutron-Ruault (Institut Gustave Roussy, Villejuif, France) and colleagues studied data from 71,248 French women included in the E3N cohort, 371 of whom developed RA during an average follow-up of 23.8 years.
A total of 46.4% of women who developed RA were never smokers, while 35.0% were former smokers, and 18.6% were current smokers at the beginning of the study. In accordance with previous results, current and former smokers were significantly more likely to develop RA than never smokers, with corresponding hazard ratios (HRs) of 1.57 and 1.32 after adjustment for age, BMI, and education.
When never smokers were categorized according to whether they had passive exposure to smoke during childhood – defined as staying in a smoky room for at least a few hours per day – those with passive exposure had a numerically higher risk for RA than never smokers with no passive exposure (adjusted HR=1.41). This difference did not reach statistical significance, but the researchers point out that “the magnitude of the increase [was] similar to that associated with active smoking, i.e.~40%.”
They also found that relative to never smokers, ever smokers (including current and former smokers) who also had passive smoke exposure during childhood had a greater degree of increased risk for RA than ever smokers with no passive exposure (adjusted HR=1.67 and 1.40, respectively).
Moreover, Boutron-Ruault and team identified an association between childhood smoke exposure and age of RA onset. Current smokers and ever smokers with passive exposure in early life had the youngest average age at disease onset, at 60.1 and 60.2 years, respectively, while never smokers with no passive exposure had the oldest, at 64.1 years.
Together, these findings “fit with the preclinical scheme of RA where an external event occurs at an early stage to promote emergence of autoimmunity, followed years after by clinical RA,” write the researchers in Rheumatology.
And they conclude: “Our results highlight the importance of avoiding any tobacco environment in children, especially in those with a family history of RA.”
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