Animal experiments have demonstrated the photocarcinogenic properties of furocoumarins, a group of naturally occurring chemicals that are rich in citrus products. We conducted a prospective study for citrus consumption and risk of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin based on data from 41530 men in the Health Professionals Follow-up Study (1986-2010) and 63759 women in the Nurses' Health Study (1984-2010) who were free of cancers at baseline. Over 24-26 years of follow-up, we documented 20840 incident BCCs and 3544 incident SCCs. Compared to those who consumed citrus products less than twice per week, the pooled multivariable-adjusted hazard ratios were 1.03 [95% confidence interval (95% CI): 0.99-1.08] for BCC and 1.14 (95% CI: 1.00-1.30) for SCC for those who consumed two to four times per week, 1.06 (95% CI: 1.01-1.11) for BCC and 1.15 (95% CI: 1.02-1.28) for SCC for five to six times per week, 1.11 (95% CI: 1.06-1.16) for BCC and 1.22 (95% CI: 1.08-1.37) for SCC for once to 1.4 times per day and 1.16 (95% CI: 1.09-1.23) for BCC and 1.21 (95% Cl: 1.06-1.38) for SCC for 1.5 times per day or more (P trend = 0.001 for BCC and 0.04 for SCC). In contrast, consumption of non-citrus fruit and juice appeared to be inversely associated with risk of BCC and SCC. Our findings support positive associations between citrus consumption and risk of cutaneous BCC and SCC in two cohorts of men and women, and call for further investigations to better understand the potential photocarcinogenesis associated with dietary intakes.
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