Niacin intake and risk of skin cancer in US women and men.

A recent clinical trial found a protective role of niacinamide, a derivative of niacin, against skin cancer recurrence. However, there is no epidemiologic study to assess the association between niacin intake and risk of skin cancer [basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and melanoma]. We prospectively evaluated whether total, dietary and supplemental niacin intake was associated with skin cancer risk based on 72,308 women in the Nurses' Health Study (1984-2010) and 41,808 men in the Health Professionals Follow-up Study (1986-2010). Niacin intake was assessed every 2 to 4 years during follow-up and cumulative averaged intake. Cox proportional hazard models were used to compute the hazard ratios (HR) and 95% confidence intervals (CI) and cohort-specific results were pooled using a random-effects model. During the follow-up, we documented 23,256 BCC, 2,530 SCC and 887 melanoma cases. Total niacin intake was inversely associated with SCC risk; the pooled HR for top vs. bottom quintiles was 0.84 (95% CI = 0.74-0.95; ptrend  = 0.08). However, there were a marginally positive association between total niacin intake and BCC risk; the pooled HR for top versus bottom quintiles was 1.05 (95% CI = 1.01-1.10; ptrend  < 0.01). Higher total niacin intake was also marginally positively associated with melanoma risk in men, but not in women. The results were similar in stratified analyses according to sun exposure related factors and by body location of melanoma and SCC. Our study supports a potential beneficial role of niacin intake in relation to SCC but not of BCC or melanoma.