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 (FAs) have divergent effects on melanoma growth, but epidemiologic evidence on their combined effect is lacking. Methods:In 634 Australian primary melanoma patients, we assessed pre-diagnosis 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 FA intakes. Prevalence ratios (PRs) and 95% confidence intervals (CIs) for the association between tertiles of dietary patterns and melanoma thickness >2mm vs ≤ 2mm were estimated using Poisson regression. Results:Overall omega-3 FA intakes were low. Two major FA dietary patterns were identified: 'meat, fish, fat', positively correlated with intakes of all FAs; and 'fish, low-meat, low-fat', positively correlated with long-chain omega-3 FA intake, and inversely with medium-chain omega-3 and omega-6 FA intakes. Prevalence of thick melanomas was significantly higher in those in the highest compared to lowest tertile of the 'meat, fish, fat' pattern (PR 1.40 95% CI 1.01-1.94), especially those with serious co-morbidity (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, 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 FA intakes, are more likely to be diagnosed with thick than thin melanomas. Impact:High omega-3 and omega-6 FA intakes may contribute to patients' presentation with thick melanomas.