Animal and experimental studies have demonstrated that long-chain
n-3 fatty acids inhibit the development of
prostate cancer, whereas
n-6 fatty acids might promote it. We performed a case-cohort analysis within the Melbourne Collaborative Cohort Study using a random sample of 1,717 men and 464
prostate cancer cases to investigate associations between
fatty acids assessed in plasma
phospholipids (PPLs) or diet (estimated using
a 121-item food frequency questionnaire) and
prostate cancer risk. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox regression.
Prostate cancer risk was positively associated with %PPL
saturated fatty acids (SFAs); HR [95% CI] = 1.51 [1.06, 2.16] (Q5 vs. Q1, fifth vs. first quintile); p-trend = 0.003. HRs (Q5 to Q2 vs. Q1) were significantly elevated for %PPL
palmitic acid. %PPL
oleic acid was inversely associated with risk, HR = 0.62 [0.43, 0.91] (Q5 vs. Q1); p-trend = 0.04. No statistically significant linear trends were observed for dietary intakes. The HRs were elevated for moderate intakes of
linoleic acid (Q2 and Q3 vs. Q1, 1.58 [1.10, 2.28] and 1.70 [1.18, 2.46], respectively), but the increase was not significant for higher intakes (Q4 and Q5). No association varied significantly by tumour aggressiveness (all p-homogeneity > 0.1).
Prostate cancer risk was positively associated with %PPL SFA, largely attributable to
palmitic acid and inversely associated with %PPL
monounsaturated fatty acids, largely attributable to
oleic acid. Higher risks were also observed for dietary n-6 polyunsaturated
fats, primarily
linoleic acid.