Fish Oil & Heart Rate

Fish oil supplementation is becoming increasingly popular and boasts claims of improving many conditions, from psoriasis to heart disease. Fish oil can be obtained by consuming oily fishes, or through supplementation with a gelatin capsule containing fish oils, which typically derive from anchovies and sardines. Fish oils contain docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are types of omega-3 fatty acids. Omega-3 fatty acids are thought to provide many health benefits, including improved heart health.
Many studies over the past decade have examined the theory that fish oil supplementation lowers heart rate. Heart rate is an important predictor of cardiac health, because a high heart rate increases one's risk of heart attack and sudden death. Because of this proposed benefit of fish oil, healthy people, those with cardiac diseases, and athletes may all stand something to gain from fish oil supplementation.

Fish Oil Reduces Heart Rate

In 2005, Mozaffarian et al. performed a meta-analysis that pooled results from 30 separate, well-designed experiments with fish oil. The analysis found that fish oil supplementation resulted in an average decrease in heart rate of 1.6 beats per minute (bpm). However, it was determined that subjects with initial heart rates above 69 bpm had an average reduction of 2.5 bpm after supplementation; thus those with a higher baseline heart rate may have more to gain from fish oil supplementation. It was also found that studies of 12 weeks or longer duration resulted in an average of 2.5 bpm reduction in heart rate after supplementation. The amount of heart rate reduction did not change significantly between studies based on the average age or health status of subjects, nor the dosage of fish oil.

In Athletes

Heart rate is an indicator of how hard you are working during exercise. Thus, many athletes, especially endurance athletes, take fish oil supplements in the hopes that a decreased heart rate during sub-maximal exercise will allow them to work less at a given power output. A 2008 study by Peoples et al. tested this hypothesis on well-trained male cyclists. The cyclists performed graded exercise tests that started at an easy level, then increased in resistance at each stage thereafter until exhaustion. Sub-maximal heart rate was lower in the cyclists after 12 weeks of fish oil supplementation, as was maximal heart rate. However, the cyclists did not increase their time to exhaustion, nor did they reach a higher stage in the tests; thus, their performance was not improved by fish oil supplementation. A 2007 study by Buckley et al. found similar results with Australian rules football players, in which sub-maximal heart rate was lowered by fish oil, but with no increases in exercise test performance. These studies indicate that although athletes will obtain the same health benefits from fish oil as non-athletes, these cardiovascular changes will not necessarily improve sport performance.

Heart Rate Variability

Heart rate variability (HRV) reflects the sensitivity of the circulatory system to changes in activity levels, emotions and any other environmental conditions. HRV is measured by taking an EKG of your heart and examining the changes in time between each heart beat. Low HRV is a risk factor for heart attack and sudden death. A study by Ninio et al. examined the effect fish oil had on HRV in sedentary, overweight adults who were at moderate to high risk for heart disease. The study found a significant increase in HRV in the fish oil group compared with the control group. This evidence shows that fish oil supplementation may improve cardiac health by increasing heart rate variability.

In Heart Attack Survivors

A 1996 study by Christensen et al. examined HRV in individuals who had survived myocardial infarction (MI), also known as a heart attack. After 12 weeks of fish oil supplementation, the HRV of the heart attack survivors increased significantly compared with both baseline and the control group. This result shows that fish oil not only improves heart health in non-diseased individuals, but can also help improve health and possibly prolong life for those who already have cardiovascular disease.

Possible Mechanisms

The processes by which fish oil supplementation decreases heart rate and increases heart rate variability have yet to be determined. However, proposed mechanisms include changes at the sinus node, an increase in heart pump efficiency, changes in the autonomic nervous system or possibly a combination of the three.
The first mechanism involves the sinus node, which is also called the "pacemaker of the heart" as this is where the heart's electrical activity originates. When you supplement with fish oils, the omega-3 fatty acids from the oils bond with the membranes of the cells in your heart. It is speculated that this bond changes the chemical activities of the sinus node, which cause it to become less excitable and thus to fire more slowly. The second theory involves the ventricles, which accomplish the main pumping action of your heart. Omega-3 fatty acids may make various changes to your cardiovascular system that increase the efficiency of your heart ventricles. If your heart can beat stronger and more easily, it does not have to beat as quickly. The final fish oil theory involves an increase in elasticity of the heart's arteries. Omega-3 fatty acids may increase sensitivity of the arterial stretch sensors, which would increase heart rate variability.