Patterns of Omega-3 and Omega-6 Fatty Acid Dietary Intake and Melanoma Thickness at Diagnosis.

Abstract

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. 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. 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. 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. High omega-3 and omega-6 fatty acid intakes may contribute to patients' presentation with thick melanomas.