Aims Previous studies have suggested a lower risk of atrial fibrillation (AF) with higher intakes of fish and marine n-3 polyunsaturated fatty acids (PUFAs), but the results have been inconsistent. The aim was to investigate the association between consumption of marine n-3 PUFA and development of AF. Methods and results A total of 57 053 Danish participants 50-64 years of age were enrolled in the Diet, Cancer, and Health Cohort Study between 1993 and 1997. Dietary intake of fish and marine n-3

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... PUFA was assessed by a semi-quantitative food frequency questionnaire. In total, 3345 incident cases of AF occurred over 13.6 years. Multivariate Cox regression analyses (3284 cases and 55 246 participants) using cubic splines showed a U-shaped association between consumption of marine n-3 PUFA and risk of incident AF, with the lowest risk of AF at a moderate intake of 0.63 g/day. For quintiles of marine n-3 PUFA intake, a 13% statistically significant lower risk of AF was seen in the middle vs. lowest quintile: Q1 reference, Q2 HR 0.92 (95% CI 0.82-1.03), Q3 HR 0.87 (95% CI 0.78-0.98), Q4 HR 0.96 (95% CI 0.86-1.08), and Q5 HR 1.05 (95% CI 0.93-1.18). Intake of total fish, fatty fish, and the individual n-3 PUFA eicosapentaenoic acid, docosahexaenoic acid, and docosapentaenoic acid also showed U-shaped associations with incident AF. Conclusion We found a U-shaped association between consumption of marine n-3 PUFA and risk of incident AF, with the lowest risk close to the median intake of total marine n-3 PUFA (0.63 g/day). ---