Fish, Omega-3 and Heart Rate Variability
Mozaffarian D. et al., Circulation. 117:1130-1137 (2008)
Division of Cardiovascular Medicine, Brigham and Women’s Hospital and Harvard Medical School, and the Departments of Epidemiology and Nutrition, Harvard School of Public Health, Boston, Mass.
Various components of heart rate variability (HRV) have been implicated in the risk of sudden cardiac death. Relatively small experimental trials have evaluated fish oil (containing DHA/EPA) and HRV with varying results likely due to small samples sizes, shorter durations of intake, limited periods of HRV assessment and differences in omega-3 dosages. In the present report, the authors hypothesize that habitual consumption of fish containing DHA/EPA may be associated with more favorable HRV which could contribute to the lower risk of death from coronary heart disease seen in various studies (and reviews thereof) with greater fish consumptions.
In this population-based cohort of older U.S. adults (men and women over 64 years of age), cross-sectional associations of dietary fish intakes and dietary DHA/EPA (summed) intakes were correlated with measures of HRV performed via ECG (electrocardiogram)-derived and 24-hour Holter monitor-derived approaches. Higher fish intakes (ranging from a low intake of <1 serving/month (mean intake of DHA/EPA of 47 mg/day) and increasing up to ≥5 servings per week (mean intake of DHA/EPA of 927 mg/day) was associated with a greater HRV as measured by SDNNECG (standard deviation of N-N intervals). The sub-group of the population with the higher intakes of fish and DHA/EPA exhibited an 11% higher average HRV (as compared to the lowest sub-group). Higher intakes were also associated with greater HRV as measured by the rMSSDECG (the root mean square of successive differences of N-N intervals). In addition to these associations with HRV reflecting short-term parasympathetic HRV, higher intakes of tuna/other fish were associated with a trend towards a higher 24-hour rMSSD reflecting average daytime and nighttime parasympathetic HRV.
The authors suggest that some of these differences in individual HRV parameters, reflective of vagally-mediated effects of fish/omega-3 fatty acids, may correspond to between a 1-8% lower risk of coronary heart disease which is considered to be a significant proportion of the approximate 35% lower risk of death due to coronary heart disease found with higher fish consumptions.
Dr. Holub's Comments:
It is necessary to point out that the higher values for the HRV parameters were generally found at fish intakes amounting to 5 or more servings per week or the equivalent of average intakes of DHA/EPA (summed) of 927 mg/day. These intakes are markedly higher than those found in a typical North American diet where a fatty fish serving is consumed once every 10-12 days on average and where the average daily intake of DHA/EPA (summed) is 120-150 mg/day. In addition, the DHA/EPA intake of 927 mg/day is almost identical with the recommended intakes from the American Heart Association for individuals with coronary heart disease (900 mg or gm daily).