Improve Your Heart Rate Variability

Summarized by Robert W. Griffith, MD
January 2, 2006

What Is Heart Rate Variability?

Heart rate variability (HRV) refers to the beat-to-beat alterations in heart rate. There is a very minor variability in the regular heart rate that depends on the respiration rate; this is called sinus rhythm. More important, however, is the change in rate due to one of two processes: (1) frequent activation in response to acute stress; and (2) inadequate response, due to over-activity of the sympathetic control of cardiac rhythm, the vagus nerve.

Why Is It Interesting?

The main reason for interest in HRV is because of its ability to predict survival after a heart attack. Studies have shown that reduced HRV predicts an increased risk of sudden death in patients with an MI (myocardial infarction, or heart attack), independent of other possible tests such as the ejection fraction. Other studies have suggested that reduced HRV may predict the risk of survival even among people who are apparently free of coronary heart disease.

It's been proposed that there's a link between negative emotions (such as anxiety and hostility) and chronic stress and reduced HRV.

How Can HRV Be Changed?

As we have seen, HRV appears to be sensitive and responsive to acute, and possibly chronic, stress. Under lab conditions, a mental load (such as making a complex decision or giving a public speech) lowers HRV. As a marker of cumulative wear and tear, HRV is also reduced along with the aging process. Although resting heart rate doesn't change significantly with advancing age, there is a decline in HRV. However, regular physical activity (which slows down the aging process) has been shown to raise HRV.

A Mexico City Study

Elderly people exposed to severe air pollution are at an increased risk for cardiovascular death - and they have reduced HRV, according to a report published in the American Journal of Respiratory and Critical Care Medicine. Air pollution is a particular problem in Mexico City, and investigators there studied possible ways of reducing the HRV level in nursing home patients, using dietary supplements.

Animal-based fatty acids were compared with plant-based fatty acids in a randomized double-blind study. Specifically, 50 nursing-home residents over 60 years of age were assigned to take two 1 gm capsules of fish oil daily (containing omega-3 polyunsaturated fatty acids [PUFA]) or two 1 gm capsules of soy oil daily (containing a preponderance of 6-omega PUFA), for 5 months.

HRV was assessed once weekly for a month before the supplements were started, and then on alternate days for the 5 months of the study proper. Ambient particulate matter was determined throughout the study as a measure of air pollution.

What the study showed

The average age of the participants was 80 years. In those allocated to take fish oil supplements, heavy air pollution during the one-month pre-supplementation period was linked to a 54% reduction in HRV. However, during the 5-month supplementation period, HRV only dropped by 7%.

On the other hand, in those taking the soy oils supplement, the reduction linked to heavy pollution during the pre-supplementation period was 46%, and there was only a 15% reduction with soy supplements.

The findings showed that fish oil supplementation was significantly better a preventing pollution-associated reduction in HRV in these elderly subjects.

How relevant are these results?

The study findings lend support to the advice given by the American Heart Association, namely that everyone should eat at least two meals a week containing oily fish. 200 to 400 grams of fatty fish a week will provide about 0.5 to 0.8 gm/day of omega-3 PUFA. Of course, this isn't as much as the amount of omega-3 PUFA taken in the study, but then the study didn't test doses lower than 2 gm/day.

The study reported showed that omega-3 PUFA (given as fish oil supplement) was superior to soy oil in helping prevent one type of stress-induced HRV reduction, at least to a certain extent. It remains to be seen if lower doses will be equally effective, and whether other causes of HRV reduction can also be influenced beneficially.

Source

• Omega-3 fatty acid prevents heart variability reductions associated with particulate matter. I. Romieu, MM. Tellez-Rojo , M. Lazo,  et al., Am J Respir Crit Care Med, 2005, vol. 172, pp. 1534--1540

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