Cardiovascular risk: DHA supplements help reduce heart rate

Supplementation with EPA and DHA can lower heart rate, that is, the number of heart beats per minute, a parameter that, if too high, can be a cardiovascular risk factor. Treatment with omega-3 supplements is associated with an average reduction in resting heart rate of more than 2 bpm (beats per minute), and when analyzed individually, it is DHA that has greater effects than EPA. Thus, omega-3 supplements could be a simple strategy to reduce mortality in general and the risk of heart disease, especially for those who do not regularly consume fish in the diet.

This is the finding of a meta-analysis study published in the European Journal of Clinical Nutrition conducted by a team of researchers from Soochow University (China). 

Cardiovascular health effects of omega-3s 

The results of this new study join those of numerous research studies, begun in the 1970s thanks to Dr. Jorn Dyerberg, that have highlighted the role of omega-3s in reducing cardiovascular risk. EPA and DHA, in fact are linked to a number of positive effects on heart and vessel health, ranging from improving blood lipid levels to reducing blood pressure and heart rate and thus the risk of coronary heart disease and cardiac death.

The potential cardioprotective effects of marine-derived omega-3 fatty acids and fish intake have been the subject of numerous studies for years, particularly with regard to sudden cardiac death. A recent meta-analysis published in the Mayo Clinic Proceedings indicated that EPA and DHA taken in foods and supplements may reduce the risk of coronary heart disease. 

Specifically, data collected from 18 clinical trials indicated that omega-3s were associated a 6 percent reduction in the risk of coronary heart disease among all populations, while the risk reduction increased up to 18 percent by evaluating data from 16 prospective studies, in which individuals who habitually consumed or did not consume omega-3s were selected and followed.

The results of clinical trials, in which omega-3 or a placebo was given to two groups of people, also showed that there was a statistically significant reduction in the likelihood of coronary heart disease in the highest risk subjects: by 16 percent in those with high triglycerides and 14 percent in those with high LDL cholesterol. A 2014 meta-analysis, reported that for untreated hypertensive subjects, omega-3 was associated with a mean reduction in systolic and diastolic blood pressure of 4.51 mmHg and 3.05 mmHg, respectively. In 2012, on the other hand, a meta-analysis conducted by Chinese researchers revealed an association between 56-day treatment with omega-3 supplements and a 2.3 percent improvement in flow-mediated dilation, a measure that indicates the ability of a blood vessel to release, and thus the "health" of the vessel itself. As mentioned, according to data from several studies, consumption of oily fish or supplementation with fish oil reduces the risk of sudden cardiac death. 

Although the exact physiological mechanisms underlying this preventive effect remain unclear, it has been suggested that omega-3s may exert a protective action on cardiac death by reducing heart rate, i.e., the number of beats the heart makes each minute. Resting heart rate if elevated is a potential risk factor for cardiovascular morbidity and mortality. The results of a study, conducted among physicians without a history of pre-existing cardiovascular disease, revealed that those who consumed fish at least once a week had a lower risk of sudden cardiac death. Moreover, baseline blood levels of omega-3 were inversely associated with sudden cardiac death in this population.

DHA significantly reduces heart rate 

To conduct the meta-analysis, which is a statistical study that includes the results of numerous research studies on a topic, the researchers collected data from 51 studies that met their inclusion criteria, considering about 3,000 people in total. The selected studies had all tested the ability of omega-3 EPA and DHA to reduce heart rate and were searched using specific databases, such as PubMed. The results obtained from the meta-analysis, indicate that omega-3 supplementation is associated with a significant reduction in heart rate, with the effects due more to DHA than EPA. Specifically, the data indicated that, compared with placebo, omega-3 supplementation was associated with a mild but significant average reduction in heart rate of 2.23 beats per minute. 

When the researchers analyzed studies that evaluated the action of EPA and DHA separately, they found that DHA was associated with an average reduction in heart rate of 2.47 bpm, while no statistically significant reduction was observed for EPA alone. According to the study authors, the present meta-analysis provides important and up-to-date clinical evidence demonstrating the effect on heart rate reduction of omega-3 supplementation. 

As the scientists pointed out, it should be considered that the heart rate of most of the participants included in this study had values within the normal range anyway. However, at the population level, the reduction in heart rate could have important public health implications, as a reduction of 3.2 bpm roughly corresponds to a 7.5 percent decrease in the risk of sudden cardiac death.

Toward more in-depth research

According to the Chinese researchers, the new study provides updated evidence on heart rate reduction by omega-3 supplementation, although this chronotropic effect is attributable only to DHA. 

Despite some limitations, the findings may have valuable clinical and public health implications; omega-3 supplements could be a useful lifestyle factor in reducing mortality and risk of heart disease, particularly in those who do not consume enough fatty fish. Therefore, future investigations are needed to assess whether heart rate reduction is associated with improvements in patients or a better public health profile. 

Source: K. Hidayat, et al. "Effect of omega-3 long-chain polyunsaturated fatty acid supplementation on heart rate: a meta-analysis of randomized controlled trials." European Journal of Clinical Nutrition. Risk of coronary artery disease and cardiac death.