Citrus peel use is associated with reduced risk of squamous cell carcinomaof the skin

Limonene has demonstrated efficacy in preclinical models of breast and colo n cancers. The principal sources of d-limonene ave the oils of orange, grap efruit, and lemon. The present case-control study was designed to determine the usual citrus consumption patterns of an older Southwestern population and to then evaluate how this citrus consumption varied with history of squ amous cell carcinoma (SCC) of the skin. In this Arizona population, 64.3% a nd 74.5% of the respondents reported weekly consumption of citrus fruits an d citrus juices, respectively. Orange juice (78.5%, orange (74.3%), and gra pefruit (65.3%) were the predominant varieties of citrus consumed. Peel con sumption was not uncommon, with 34.7% of all subjects reporting citrus peel use. We found no association between the overall consumption of citrus fru it (odds ratio (OR) = 0.99, 95% confidence interval (CI) = 0.73-1.32] or ci trus 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 relatio nship between higher citrus peel in the diet and degree of risk lowering. T his is the first study to explore the relationship between citrus peel cons umption and human cancers. Our results show that peel consumption, the majo r source of dietary d-limonene, is not uncommon and may have a potential pr otective effect in relation to skin SCC. Further studies with large sample sizes are needed to more completely evaluate the interrelationships between peel intake, bioavailability of d-limonene, and other lifestyle factors.