Objective To evaluate the associations between body mass index (BMI), weight change, waist circumference, hip circumference and risk of incident psoriasis.
Methods A prospective study of female nurses who were followed up over a 12-year period (1996–2008) in Nurses’ Health Study, a cohort of 121 700 US women at the inception in 1976. The study included 67 300 women who responded to a question about a history of physician-diagnosed psoriasis in last 12 years in 2008 (mean age at 1996, 62 years). The primary outcome was self-reported, physician-diagnosed psoriasis.
Results During the 12 years of follow-up, there were a total of 809 incident psoriasis cases. There was a graded positive association between BMI (both baseline and updated) and the risk of psoriasis (both P values for trend <0.0001). Compared to women with updated BMI of <25, the multivariate relative risks (RRs) of incident psoriasis were 1.21 (95% CI, 1.03–1.43) for a BMI of 25.0–29.9, 1.63 (95% CI, 1.33–2.00) for a BMI of 30.0–34.9 and 2.03 (95% CI, 1.58–2.61) for a BMI of 35.0 or greater. Higher waist circumference, hip circumference and waist–hip ratio were associated with a higher risk of incident psoriasis, but became non-significant after additionally adjusting for BMI. The BMI at age of 18 years was not associated with the risk of psoriasis. Weight gain since the age of 18 years was associated with an increased risk of psoriasis, and RR of 10 lb gain was 1.08 (95% CI, 1.06–1.11; P < 0.0001).
Conclusion This large prospective study indicates that higher BMI and weight gain are risk factors for incident psoriasis in older US women.