Patterns of omega-3 and omega-6 fatty acid dietary intake and melanoma thickness at diagnosis

Abstract

Background: Experimental evidence suggests that dietary intakes of omega-3 and omega-6 polyunsaturated fatty acids have divergent effects on melanoma growth, but epidemiologic evidence on their combined effect is lacking. Methods: In 634 Australian patients with primary melanoma, we assessed prediagnosis consumption of 39 food groups by food frequency questionnaires completed within 2 months of diagnosis. We derived, by reduced rank regression, dietary patterns that explained variability in selected omega-3 and omega-6 fatty acid intakes. Prevalence ratios (PR) and 95% confidence intervals (CI) for the association between tertiles of dietary patterns and melanoma thickness >2 mm versus ≤2 mm were estimated using Poisson regression. Results: Overall omega-3 fatty acid intakes were low. Two major fatty acid dietary patterns were identified: "meat, fish, and fat," positively correlated with intakes of all fatty acids; and "fish, low-meat, and low-fat," positively correlated with long-chain omega-3 fatty acid intake, and inversely with medium-chain omega-3 and omega-6 fatty acid intakes. Prevalence of thick melanomas was significantly higher in those in the highest compared with lowest tertile of the "meat, fish, and fat" pattern (PR, 1.40; 95% CI, 1.01-1.94), especially those with serious comorbidity (PR, 1.83; 95% CI, 1.15-2.92) or a family history (PR, 2.32; 95% CI, 1.00-5.35). The "fish, low-meat, and low-fat" pattern was not associated with melanoma thickness. Conclusions: People with high meat, fish, and fat intakes, who thus consumed relatively high levels of omega-3 and high omega-6 fatty acid intakes, are more likely to be diagnosed with thick than thin melanomas.