Introduction:
Omega-3 fatty acid levels are associated with decreased risk for sudden death; however, the protective cardiovascular mechanisms of omega-3 are poorly understood.

This study addresses the heart rate variability (HRV) changes in a cohort of elderly subjects randomized to receive either a daily high dose of marine-derived omega-3 fatty acids (fish oil) or a lower daily dose of a plant-derived omega-3 fatty acid (alpha-linolenic acid) in soy oil.

Methods:
A total of 58 elderly nursing home residents were randomized to receive 2 g/d of fish oil capsules vs 2 g/d of soy oil capsules, and were subsequently followed up every other day for a period of 6 months with 6-min measurements of HRV while resting supine.
An initial control period of 2 months without supplementation was allowed to establish an HRV baseline for each participant.

Results:
The average time- and frequency-domain parameters of HRV increased significantly during the supplementation period in both the fish oil and soy oil groups.
In the regression model after adjusting for age and mean heart rate, supplementation with fish oil was associated with a significant increase in the high- and low-frequency components, and SD of normal RR intervals (SDNN), whereas only SDNN increased significantly in the soy oil group.

Conclusions:
Supplementation with 2 g/d of fish oil was well tolerated and was associated with a significant increase in HRV. Supplementation with 2 g/d of soy oil was associated with a lesser but significant increase in HRV.

PMID 15821181

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