Serum Long-Chain n-3 Polyunsaturated Fatty Acids, Mercury, and Risk of Sudden Cardiac Death in Men: A Prospective Population-Based Study

Objectives: Fish consumption has been associated with reduced risk of cardiovascular diseases (CVD), especially sudden cardiac death (SCD). Fish is the major source of long-chain n-3 polyunsaturated fatty acids (PUFA) eicosapentaenoic acid and docosahexaenoic acid. It is also a major source of methylmercury, which was associated with increased risk of CVD in this study population. Impact of interaction between long-chain n-3 PUFA and methylmercury on the SCD risk is unknown. Methods: A total of 1857 men from the prospective, population-based Kuopio Ischaemic Heart Disease Risk Factor study, aged 42-60 years and free of CVD at baseline in 1984-1989, were studied. Serum long-chain n-3 PUFA was used as the marker for long-chain n-3 PUFA intake and hair mercury as the marker for mercury exposure. Results: During the mean follow-up of 20.1 years, 91 SCD events occurred. In the multivariate Cox proportional hazards regression models, serum long-chain n-3 PUFA concentration was not associated with the risk of SCD until hair mercury was accounted for; then the hazard ratio (HR) in the highest vs. lowest tertile was 0.54 [95% confidence interval (CI) 0.32 to 0.91, p for trend = 0.046]. When the analyses were stratified by hair mercury content, among those with lower hair mercury, each 0.5 percentage unit increase in the serum long-chain n-3 PUFA was associated with HR of 0.77 (95% CI 0.64 to 0.93), whereas no association was seen among those with higher hair mercury (p for interaction = 0.01). Among the individual long-chain n-3 PUFA, docosahexaenoic acid was most strongly associated with the risk. Conclusion: High exposure to mercury may reduce the benefits of long-chain n-3 PUFA on SCD.