To study the association of cigarette smoking with risk of rheumatoid arthritis (RA), among 377,481 female health professionals in the Women's Health Cohort Study.
Subjects completed mailed questionnaires regarding demographics, health habits, including cigarette smoking history, and medical history, including RA diagnosis made by a physician and date of diagnosis. Of 7,697 women who self-reported RA, 3,416 reported seropositive RA. Cox proportional hazards regression models were used to retrospectively assess the associations of smoking intensity and duration with the risk of developing RA or seropositive RA. Cigarette smoking status was treated as a time-varying exposure in these regression models.
In multivariate analyses controlling for age, race, education, age at menarche, pregnancy history, menopausal status, and postmenopausal hormone use, duration of smoking was associated with a significantly increased risk of both RA and seropositive RA (both P < 0.01 for trend), after adjusting for smoking intensity. Women who smoked > or =25 cigarettes/day for more than 20 years experienced a 39% increased risk of RA and 49% increased risk of seropositive RA. However, smoking intensity (number of cigarettes/day) was unrelated to risk of RA or seropositive RA (both P = 0.3 for trend), after adjusting for duration of smoking.
Duration, but not intensity, of cigarette smoking is associated with a modest increased risk of RA in women.