Ruminant Fatty Acids and Prostate Cancer Risk in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study

Consumption of high fat animal products is a characteristic feature of Western diets, which have been consistently linked with elevated risks of prostate cancer. In order to elucidate which specific fatty acids may contribute to this association, we measured circulating concentrations of myristic (C14:0), pentadecanoic (C15:0), palmitic (C16:0), heptadecanoic (C17:0), vaccenic (C18:1n-7), and alpha-linolenic (C18:3n-3) acids - all of which are present in ruminant meat and/or dairy products - in a nested case-control study within the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study. Prediagnostic blood samples from 300 prostate cancer cases and 300 controls matched on age and date of serum blood draw were analyzed for the aforementioned fatty acids by gas chromatography-mass spectrometry. There was a positive association between serum alpha-linolenic acid and overall prostate cancer risk, with a notable threshold effect (for increasing quartiles, odds ratios and 95% confidence intervals = 1.0 (referent), 1.65 (1.02–2.67), 1.96 (1.22–3.14), and 1.57 (0.97–2.54); p trend = 0.15). This association was stronger among men with low baseline levels of beta-carotene and vitamin E. The other fatty acids were unrelated to prostate cancer risk. Our findings indicate that higher blood levels of alpha-linolenic acid - the predominant omega-3 fatty acid in Western diets - is associated with elevated risks of prostate cancer, particularly within subgroups of men with low antioxidant levels.