Citrus Peel Use Is Associated With Reduced Risk of Squamous Cell Carcinoma of the Skin

Abstract: Limonene has demonstrated efficacy in preclinical models of breast and colon cancers. The principal sources of d-limonene are the oils of orange, grapefruit, and lemon. The present case-control study was designed to determine the usual citrus consumption patterns of an older Southwest-ern population and to then evaluate how this citrus con-sumption varied with history of squamous cell carcinoma (SCC) of the skin. In this Arizona population, 64.3 % and 74.5 % of the respondents reported weekly consumption of citrus fruits and citrus juices, respectively. Orange juice (78.5%), orange (74.3%), and grapefruit (65.3%) were the predominant varieties of citrus consumed. Peel consumption was not uncommon, with 34.7 % of all subjects reporting cit-rus peel use. We found no association between the overall consumption of citrus fruits [odds ratio (OR) 0.99, 95% confidence interval (CI) 0.73–1.32] or citrus juices (OR 0.97, 95 % CI 0.71–1.31) and skin SCC. However, the most striking feature was the protection purported by citrus peel consumption (OR 0.66, 95 % CI 0.45–0.95). Moreover, there was a dose-response relationship between higher cit-rus peel in the diet and degree of risk lowering. This is the first study to explore the relationship between citrus peel consumption and human cancers. Our results show that peel consumption, the major source of dietary d-limonene, is not uncommon and may have a potential protective effect in re-lation to skin SCC. Further studies with large sample sizes are needed to more completely evaluate the interrelation-ships between peel intake, bioavailability of d-limonene, and other lifestyle factors