Heart rate variability and fatty acid content of blood cell membranes: a dose-response study with n-3 fatty acids

Background: Dietary intake of long-chain n-3 polyunsaturated fatty acids (PUFA) may protect against sudden cardiac death, an event that may be predicted by measurement of heart rate variability (HRV). Objective: The objectives of this study were to 1) examine the correlations between the content of fatty acids in blood cell membranes (platelets and granulocytes) and HRV in healthy subjects, and 2) assess the effect on HRV of dietary intervention with n-3 PUFA in different doses. Design: Sixty healthy volunteers (25 women and 35 men) were randomly assigned to 3 treatment groups in a double-blind design. Subjects received a daily supplement of either 6.6 g n-3 PUFA, 2.0 g n-3 PUFA, or placebo (olive oil). A 24-h Holter recording was obtained for each subject before supplementation and after 12 wk of supplementation; the 24-h HRV was then related to the content of fatty acids in granulocytes and platelets. Results: Before supplementation, positive correlations were observed in men between the content of docosahexaenoic acid in cell membranes and HRV indexes (r = 0.50, P < 0.01), whereas such correlations were not found in women. Dietary intervention revealed a dose-dependent effect of n-3 PUFA on HRV in men, whereas no effect was found in women. Conclusion: The study showed a beneficial effect of n-3 PUFA on HRV in healthy men, suggesting an antiarrhythmic effect of n-3 PUFA. No such effect was observed in healthy women.