Long-chain, n-3 fatty acids and physical activity--independent and interactive associations with cardiac autonomic...

Intake of the marine-based, n-3 fatty acids and engagement in physical activity are inversely related to cardiac morbidity and mortality. Among putative mechanisms, both n-3 fatty acids and physical activity may act through modulation of autonomic control of the cardiovascular system. This investigation examined the independent and interactive associations of n-3 fatty acids (eicosapentaenoic and docosahexanenoic acid; EPA, DHA) and physical activity with heart rate variability (HRV).

Subjects were 259 healthy 30-54 year-old adults. Serum phospholipid fatty acid composition was employed as a biomarker of dietary n-3 fatty acid exposure. Physical activity based on the Paffenbarger questionnaire was coded as < or ≥ 2000 kcal/week. Standard time-domain (standard deviation of normal-to-normal intervals and root-mean squared of successive differences; SDNN, RMSSD) and frequency domain (high frequency and low frequency power) measures of HRV were derived from resting electrocardiographic recordings.

In linear regression models with covariate adjustment for age, gender and race, greater n-3 fatty acid exposure was associated with greater SDNN and RMSSD, and high physical activity was associated with greater RMSSD. n-3 fatty acid exposure also predicted variation in SDNN, RMSSD, and high-frequency power in interaction with physical activity. Specifically, n-3 fatty acid exposure covaried positively with these three HRV indices only among participants expending 2000 kcal per week or more in physical activity. These latter findings were noted for DHA but not EPA.

These results suggest that the cardiovascular benefits of n-3 fatty acid consumption may be mediated, in part, by effects on cardiac autonomic control and may be dependent upon concomitant habitual exercise.