Background: Psoriasis is a common, chronic, inflammatory skin disorder. Higher adiposity may increase the risk of psoriasis, but, to our knowledge, no prospective data are available on this relationship.
Methods: We prospectively examined the relationships between body mass index (BMI [calculated as weight in kilograms divided by height in meters squared]), weight change, waist circumference, hip circumference, waist-hip ratio, and incident psoriasis in 78 626 women over a 14-year period (1991-2005) in the Nurses' Health Study II. The primary outcome was incident, self-reported, physician-diagnosed psoriasis.
Results: During the 14 years of follow-up, there were 892 self-reported incident cases of psoriasis. There was a graded positive association between BMI measured at multiple time points and the risk of incident psoriasis. When we analyzed BMI updated every 2 years, compared with a BMI of 21.0 through 22.9, the multivariate relative risks of psoriasis were 1.40 (95% confidence interval [CI], 1.13-1.73) for a BMI of 25.0 through 29.9; 1.48 (95% CI, 1.15-1.91) for a BMI of 30.0 through 34.9; and 2.69 (95% CI, 2.12-3.40) for a BMI of 35.0 or greater (P for trend, < .001). For BMI at the age of 18 years, the multivariate relative risk for the top BMI category (> or = 30.0) was 1.73 (95% CI, 1.24-2.41) and that for a lower BMI category (< 21.0) was 0.76 (95% CI, 0.65-0.90) (P for trend, < .001). Weight gain from the age of 18 years, higher waist circumference, hip circumference, and waist-hip ratio were all associated with a higher risk of incident psoriasis (all P values for trend, < .001).
Conclusion: This large prospective study indicates that increased adiposity and weight gain are strong risk factors for incident psoriasis in women.