No association between vitamin D intake and incident psoriasis among US women

We investigated the association between dietary, supplementary and total vitamin D intake and incident psoriasis in women. A prospective study was performed of 70,437 US female nurses aged 47-74 enrolled in the Nurses' Health Study who did not have psoriasis at baseline in 1994 and who completed semi-quantitative food frequency questionnaires in 1994, 1998, 2002 and 2006. The incidence of clinician-diagnosed psoriasis was ascertained and validated by self-reported questionnaires. 502 confirmed incident psoriasis cases were documented during 973,057 person-years of follow-up from 1994 June to 2008 June. Association between vitamin D intake and incident psoriasis was assessed using multivariable-adjusted cox regression analysis. After adjusting for age, smoking, body mass index, calorie intake, UV flux, exercise and alcohol use, there was no significant association between vitamin D intake (dietary, supplementary and total vitamin D) and the risk of incident psoriasis. Compared with women whose dietary vitamin D intake was <100 IU/day, multivariate relative risks for psoriasis was 1.13 (95 % CI 0.66-1.92) for ≥400 IU/day (P trend = 0.88). The multivariate relative risk for women who took supplementary vitamin D ≥400 IU/day was 1.18 (95 % CI 0.88-1.58) compared with women who did not take supplementary vitamin D. The multivariate risk for women who had total vitamin D intake of 300-399 IU/day was no different than at higher and lower doses of vitamin D intake. Our study does not support preventive roles of dietary or supplemental vitamin D intake for incident psoriasis.