Heart Rate Variability

The lack of omega-3 fatty acids in the vegan diet results in low heart rate variability (HRV). It has been shown that a low HRV leads to increased risk of mortality after a heart attack as well as other cardiac-related events.

 

Long-chain omega-3 polyunsaturated fatty acids (PUFA) have gained a reputation as a cardiovascular friendly food component that helps lower inflammation and triglyceride levels. Omega-3 fatty acids are comprised of alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA is found in plant oils, while EPA and DHA are both found in marine-based oils from fish and algae. Mammals cannot synthesize omega-3 fatty acids, but can synthesize them from the diet. The consumption of ALA allows the synthesis of EPA, which is used to make DHA. However, there is a catch, the conversion from ALA to EPA is very low, from undetectable amounts up to 4% in men and 9% in women. Cardiovascular health and inflammation benefits are attributed to EPA and DHA, not ALA.

A low heart rate variability (HRV), a measure of how much the heart rate changes over time, has been associated with mortality after heart attacks as well as heart failure, depression, diabetes-related nerve damage, and post-cardiac transplant. Normally, the heart rate increases due to input from the sympathetic nervous system (SNS) and decreases due to input from the parasympathetic nervous system (PSNS). A raised heart rate can also result from high SNS activity and suppressed PSNS.

Fish oil, which is high in EPA and DHA, has been shown to reduce heart rate in humans. It has been shown that EPA and DHA increase cell membrane fluidity of the cardiac tissue and nerves affecting heart rate, altering ion channel currents and reducing pacemaker activity in experiments with rabbits. Since HRV is under the control of the SNS and PSNS, regulation of the heart rate may be influenced by the omega-3 fatty acid status of neuronal and cardiac tissue.

The authors of a novel study published in the British Journal of Nutrition hypothesized that vegans have higher heart rates with shorter interbeat intervals (IBI) and lower HRV than omnivores due to a lack of EPA and DHA in their diet. Heart rate, blood and plasma levels of EPA and DHA (and their metabolites) were measured in 23 vegans and 24 omnivores, aged 40-70 years old. Researchers were particularly interested in the status of EPA and DHA in blood cell membranes, as each cell has a 4-month lifespan and indicates long-term incorporation of the fatty acids.

The results showed significant differences in the omega-3 fatty acid status of each group. Vegans had greater blood concentrations of ALA metabolites than omnivores, and very low to undetectable levels of EPA and DHA metabolites. These results support evidence that higher dietary intake of linoleic acid, an omega-6 fatty acid consumed in much greater quantities by vegans, may inhibit conversion of ALA to EPA and DHA. The daytime heart rate was higher (2 bpm faster), IBI was shorter (-67ms), and HRV was lower in vegans. There were no sleep-time differences in these parameters. These results suggest that low omega-3 status may result in higher SNS activity and/or a withdrawal of PSNS activity.

The limitations of this study are the low number of participants sampled and the need to confirm the association of low omega-3 with low HRV in a randomized trial with EPA and DHA supplementation in vegans.

 

Written By: Kenneth Dominguez, PhD

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