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.
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.
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 (≥ 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).
This large prospective study indicates that increased adiposity and weight gain are strong risk factors for incident psoriasis in women.