Can Fish Oil Really Protect the Heart?

This article is an excerpt from “Clinical Insights:  New Knowledge on Heart Disease Prevention and Treatment, Volume 3.”, written by Prof Tan Huay Cheem, Chairman of the Singapore Heart Foundation and Senior Consultant Cardiologist at the National University Heart Centre, Singapore.

Fats consumed through food may be broadly categorised into two types: saturated fats and unsaturated fats. Saturated fats mostly come from animal meats, while unsaturated fats are predominantly found in fish and plant oils. The idea that fish oil might protect the heart originated from observations of the Eskimos living in Greenland. Epidemiological studies in the 1970s revealed that Eskimos had a cardiovascular disease death rate of only 3.5%, which is much lower than that of other populations. Despite their high-fat diet, primarily from animal sources, they had normal cholesterol and triglyceride levels.

Scientists speculated that this might be related to their diet, which included a significant amount of fish and marine mammals like seals. Studies showed that every day they consumed an average of 500 grams of fish or whale meat, which contained about 7 grams of fish oil. Similarly, the Japanese also consume an average 100 grams of fish per day; and they have a low incidence of cardiovascular disease.

A Certain Dose Of Fish Oil Lowers Triglycerides

Fish oil differs significantly from animal fats; its fat content consists mainly omega-3 (n-3) polyunsaturated fatty acids, notably eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). DHA, a metabolite of EPA, is present in lower quantities in fish but has almost the same clinical effects as EPA. Since the human body cannot synthesise DHA and EPA, they are known as “essential fatty acids” and must be obtained from diet; they are crucial for maintaining the structure and function of tissues such as the retina and the brain.

Another n-3 unsaturated fatty acid, alpha-linolenic acid (ALA), found in nuts, seeds, grains, and plant oils, could be converted into DHA and EPA in the body. However, the conversion rate from ALA to DHA and EPA is minimal, so consuming fish such as salmon, sardines, and tuna is more effective in meeting DHA and EPA needs.

Fish oil has various biochemical functions, but its most notable effect is reducing triglycerides in the blood. While normal dietary fish oil levels do not affect blood lipid levels, increasing fish oil intake correlates with a decrease in triglyceride concentrations. Fish oil can also lower blood pressure and heart rate, reduce platelet aggregation, and decrease thrombus formation. Although clinical trials have not confirmed fish oil’s anti-arrhythmic properties, some people believe it may reduce arrhythmias and sudden death.

A 2014 study led by the National University of Singapore’s School of Public Health investigated the relationship between fish oil intake and heart disease. The study included 60,000 healthy Chinese participants and tracked them for 18 years. The results showed a 17% reduction in cardiovascular-related mortality among the top 25% of n-3 fatty acid consumers compared to the bottom 25%. Over 30 years, various studies have demonstrated that consuming fish or fish oil could reduce mortality from cardiovascular disease, including fatal heart attacks and sudden death. In the 1990s, Kromhout first published that fish had a preventive effect on coronary heart disease, and this attracted wide attention. The GISSI trial, the largest study, showed a 35% to 45% reduction in cardiac mortality and sudden death, though the benefit is most pronounced in the first nine months after a heart attack. This suggests that fish oil’s secondary prevention effect for coronary heart disease is better than its primary prevention effect; this means fish oil is more effective for individuals with existing cardiovascular disease.

The benefits of fish oil are consistent across different ages, genders, and ethnic groups. In addition to preventing heart attacks and sudden death, fish oil could also slow down the progression of heart failure and extend lifespan. However, fish oil does not reduce the risk of stroke, atrial fibrillation, or recurrent arrhythmias.

Fish or Fish Oil Pills?

Given the benefits of fish oil for cardiovascular health, the question is, which is the better method of consumption: eating fish or taking fish oil supplements? Most research is based on eating fish rather than on taking supplements. Fish provides protein, vitamins, and minerals beneficial to health, thereby making it the preferred choice. Fish oil supplements should be considered only if eating fish is not feasible because of specific reasons. Some deep-sea fishes, such as albacore tuna, swordfish, and shark, contain higher mercury levels, and so raises concerns about mercury poisoning. However, there is no evidence that mercury in fish increases the risk of cardiovascular disease. Overall, eating fish is more beneficial than harmful for cardiovascular health. Governments should focus on protecting marine environments, and on ensuring sustainable fisheries so as to maintain fish quality and availability.

How much n-3 unsaturated fatty acid should we consume daily? European and American guidelines generally recommend at least 250 micrograms (mg) of EPA+DHA daily or consuming fatty fish twice a week, with at least 3.5 ounces (as advised by the American Heart Association). The Health Promotion Board of Singapore also recommends eating fish twice a week. Pregnant women and children should avoid fish with high mercury content and consider fish oil supplements (without mercury) as an alternative. There are many types of fish oil supplements in the market; these have EPA+DHA content ranging from 300 to 800 micrograms per gram. Patients with high triglycerides may need 3 to 12 grams of EPA+DHA daily to manage their condition. Large quantities of fish oil supplements may cause bad breath or a fishy taste. Using frozen supplements or taking them with meals could help, and trying different brands or taking them at night is also beneficial.

Current research supports that eating fish or taking n-3 unsaturated fatty acids (fish oil) could prevent cardiovascular disease and reduce mortality risk. However, ecological changes, regional and cultural differences, and individual food preferences make it difficult to implement fish consumption universally for protection against cardiovascular disease. Nonetheless, high-risk cardiovascular individuals should eat more fish and complement their diets with healthy foods like vegetables, grains, plant oils, and dairy to maximise the benefits. Doctors should encourage patients to eat more fish: and governments and public health organisations should promote fish consumption to protect cardiovascular health.