PROSPECTIVE-STUDY OF PLASMA FATTY-ACIDS AND RISK OF PROSTATE-CANCER

Background: Although some evidence suggests that dietary fat intake is related to prostate cancer, epidemiologic studies have been inconsist ent. Purpose: Our purpose was to assess the association between plasma lipid levels, particularly linoleic and alpha-linolenic acids, and th e development of prostate cancer. Methods: In 1982, at the start of th e Physicians' Health Study, 14916 U.S. male physicians provided plasma samples, which were frozen at -82-degrees-C. Data accumulated from a series of questionnaires were used to assess the intake of various foo ds. We used a nested case-control design to compare the fatty acid com positions in plasma from 120 men who later developed prostate cancer w ith 120 matched controls who did not. Individual fatty acids were meas ured in plasma as a percentage of total fatty acids, using capillary g as chromatography. Conditional logistic regression models were used to obtain odds ratio estimates while adjusting simultaneously for the ef fects of one or more potential confounders. Results: The relative risk s (RRs) of prostate cancer for men in successively higher quartiles of plasma alpha-linolenic acid level were 3.0 (95% confidence interval [ CI] = 1.2-7.3), 3.4 (95% CI = 1.6-7.5), and 2.1 (95% CI = 0.9-4.9), co mpared with those with levels below the detection threshold (P trend = .03). For linoleic acid, RRs in successively higher quartiles were 0. 7 (95% CI = 0.4-1.5), 0.8 (95% CI = 0.4-1.6), and 0.6 (95% CI = 0.3-1. 3), with the lowest quartile as referent (P trend = .24). The effect e stimates were not notably altered by adjustment for exercise, body mas s, meat and dairy consumption, or other fatty acid levels in the plasm a. The RR for eating red meat at least five times per week compared wi th less than once a week was 2.5 (95% CI = 0.9-6.7) and was little cha nged by adjustment for alpha-linolenic acid, although alpha-linolenic acid levels were correlated with intake of red meat and butter. The as sociation of alpha-linolenic acid levels with prostate cancer was grea ter among men with low linoleic acid and reduced meat intake. Conclusi ons: These results suggest that low plasma levels of alpha-linolenic a cid might be associated with reduced risk of prostate cancer, independ ently of high meat intake. High linoleic acid and low marine fatty oil s were not associated with increased risk, as previously hypothesized. Implications: The effects of dietary alpha-linolenic acid, particular ly from vegetable sources, warrant further study. The effects of dieta ry linoleic acid and marine fatty acids seen in animal bioassays might not apply to human prostate cancer.