Objective Higher marine-derived n-3 fatty acids (MDn3FAs) intake reduces the risk of sudden cardiac death via antiarrhythmic effects. The article evaluates whether MDn3FAs intake attenuates the increased risk of cardiac death associated with J-point elevation (JPE), characterised by an elevation of QRS-ST junction (J-point) ≥0.1 mV on electrocardiography.

Design A prospective population-based cohort study.

Setting The National Survey on Circulatory Disorders and the National Nutrition Survey of Japan.

Participants A total of 4348 community-dwelling men (mean age 49.3 years), without cardiovascular diseases at baseline, from randomly selected areas across Japan.

Main outcome measures Cardiac death (200 men) during the 24-year follow-up.

Results Dietary MDn3FAs intake was assessed using a dietary method to estimate individual intake of household-based weighed food records for 3 days. Cox models were used to calculate HRs and 95% CIs adjusted for possible confounding factors. JPE was present in 340 participants (7.8%). The median daily intake of MDn3FAs was 0.35%kcal (0.92 g/day). The risk of cardiac death was significantly higher in participants with JPE than in those without JPE in the low intake group (<0.35%kcal; adjusted HR 3.51; 95% CI 1.84 to 6.73; p<0.001), but not in the high intake group (≥0.35%kcal; adjusted HR 1.09; 95% CI 0.56 to 2.16; p=0.795). The interaction between dietary MDn3FAs intake and JPE on the risk of cardiac death was statistically significant (p=0.006).

Conclusions The increased risk of cardiac death associated with JPE may be attenuated by higher dietary MDn3FAs intake.