Randomized clinical trials of supplementation with omega-3 capsules have shown conflicting outcomes regarding their beneficial effects on the prevention of heart disease.
Millions of people across the globe consume omega-3 fatty acids as supplements, thinking the intake will help them prevent heart disease. The global market for omega-3 supplements was worth around $31 billion in 2015.
Omega-3 fatty acids contain two long-chain fats: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are found in oily fish such as salmon, sardines, and mackerel. Nuts and seeds, and in particular walnuts and rapeseed oil, contain another sort of omega-3 called alpha-linolenic acid (ALA). The protection offered by these omega-3 fatty acids against cardiovascular disease is said to be due to their effects on decreasing triglyceride levels, inflammation, blood clotting, and irregular heartbeats.
Overall, it is clear that there is more clinical evidence of little or no effect of Omega-3 supplements intake than proof of beneficial effects that lead to reducing the risk of heart disease. Nevertheless, these clinical trials do not exclude the health benefits of having oily fish as part of a healthy balanced diet that protects the heart.
But is there clinical evidence that omega-3 supplements reduce the risk of developing heart disease?
Early observational clinical studies demonstrated that regular consumption of fish (oily fish in particular) is associated with a reduced risk of heart disease in many populations such as Greenland Eskimos. Since oily fish is rich in omega-3 fatty acids, it was suggested that these omega-3 fatty acids are the active constituents in fish oil that protect against heart disease. However, randomized clinical trials of supplementation with omega-3 capsules showed conflicting outcomes regarding their beneficial effects on the prevention of heart disease or death due to heart disease.
Recently, Dr. Lee Hooper, Nutrient Expert and Reader at the University of East Anglia in the United Kingdom (UK), led an extensive systematic review of 79 randomized trials involving 112,059 people. These clinical trials assessed the effects of consuming omega-3 supplements (1-gram per day) on the risk of heart and circulatory disease and compared them with those of average or lower intake of omega-3. All the trials reviewed included mixed populations who had participated in the trial for an extended period. The results of the Hooper review showed that taking omega-3 (fish oil, EPA, or DHA) supplements does not benefit heart health or reduce the risk of stroke or death from any cause.
A more recent clinical randomized trial (ASCEND), conducted by a collaborative study group of independent investigators from the University of Oxford, UK has found no effect on cardiovascular events or mortality. The study involved 15,480 diabetic patients with no cardiovascular disease at baseline (diabetics at high risk of heart disease). They were randomly assigned omega-3 supplements (1g per day) or placebo and were followed for around seven years.
Another ongoing clinical trial (named VITAL) in which 25,871 healthy middle-aged men and women across the United States are taking daily supplements of omega-3 fatty acids (1g) over five years has not resulted in a lower incidence of major cardiovascular events in this population. Interestingly, in the same study, it was reported that people with low dietary intake of fish at baseline have a more significant cardiovascular benefit from omega-3 fatty acid supplementation.
While the evidence coming from observational population studies in which diets with a high content of oily fish are linked to lower risk of heart disease is consistent, it remains difficult to conclusively isolate a single element among the benefits of eating fish. Indeed, the cardiovascular effects of eating more oily fish may differ from those of taking omega-3 supplements because fish is a rich source of other essential elements and nutrients including iodine, zinc, calcium, and protein. Also, fish is often consumed as part of a healthy diet and as a substitute for other foods, including sources of saturated fats, which are associated with a higher risk of heart disease.
Importantly, the American Heart Association (AHA) Guidelines 2018 recommended that the general public eats two servings of non-fried oily fish per week to help reduce the risk of cardiovascular disease. The guidelines restricted the use of omega-3 supplements for specific categories of cardiovascular patients. In contrast, the UK guidelines issued by the National Institute for Health and Care Excellence (NICE) encourage people to consume at least two portions of non-fried fish (200g) per week, including a portion of oily fish to prevent cardiovascular disease rather than taking omega-3 supplements. The recommended fish servings will cover the daily allowance of an adult, 0.3 to 0.5 g of omega-3 (EPA and DHA).
Evidence-based research concludes that a daily omega-3 supplementation does not help to prevent heart disease or death. Still, there is a consensus that clearly indicates there are health benefits from eating oily fish; even if that is simply because it displaces unhealthier foods.