Fish oil pills are the third most-bought food supplement, after vitamins and minerals, and are bought by 10 percent of North Americans at a cost of about $1.2 billion each year. Fish oil pills have not been shown to help prevent heart attacks, even though people who eat fish have been shown to have a reduced incidence of heart attacks. You get your maximum protection from eating fish twice a week. Eating fish more often than that has not been shown to offer further protection from heart attacks.
Fish oil pills are among the most unstable supplements on the market because the oil oxidizes quickly when exposed to oxygen. Fish oils contain omega-3 fatty acids that are unusually susceptible to being oxidized to products that can be harmful (J Nutr Sci, November 23, 2015;4:e36). This study showed that 50 percent of fish oil pills in Canada exceeded the voluntary limits for at least one measure of oxidation, and 39 percent exceeds the international voluntary safety recommendations for total oxidation. In another study, 27 percent of fish oil products tested in South Africa were found to have more than twice the recommended levels of lipid peroxides (Cardiovasc J Afr, 2013;24:297–302), and more than 80 percent of supplements tested in New Zealand exceeded recommended levels (Sci Rep, 2015;5:7928).
The reason scientific studies today have failed to show that fish oil pills prevent heart attacks may be that the harm from rancid fish oil pills offsets any benefits the pills may offer. The oxidized oils have a stale-fish odor, so if you break open a fish oil capsule and it smells or tastes fishy, it is rancid and should be discarded. Even if you buy a brand that you trust, check each bottle because one batch can be fresh while the next batch is rancid.
Oxidants and Antioxidants
Many foods that you eat and chemicals in your body are harmless, but when exposed to oxygen, they combine with the oxygen to form harmful oxidized substances. That is why you hear so much about antioxidants that can help to get rid of the oxidized chemicals . An example of an oxidized substance that is harmful is LDL cholesterol that doctors use to predict susceptibility for a heart attack. LDL cholesterol is really harmless; it becomes harmful only after the fats in it are oxidized to form oxidized LDL cholesterol. More at Cholesterol and Oxycholesterol
Evidence that Fish Oil Pills Do Not Prevent Heart Attacks
A review of more than 24 scientific studies on fish oil pills found that all but two showed that fish oil pills were no more effective than placebo pills in preventing heart attacks or strokes (JAMA Intern Med, 2014;174(3):460-462). A study of more than 12,000 people showed that a gram of fish oil daily did not prevent death from heart attacks and strokes (New England Journal of Medicine, March 9, 2013). Another study reviewed 14 studies that were randomized, placebo-controlled and involved 20,485 people and found that fish oil pills did not reduce the risk of heart attacks or death from heart attacks in patients who already had heart disease (Arch Intern Med, 2012;172(9):686-694).
How Eating Fish May Help to Prevent Heart Attacks
Fish oils contain two omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), that help to prevent clotting. Clots are the primary cause of heart attacks. First you suffer inflammation where your overactive immunity punches holes in the inner linings of your arteries. The holes bleed and clot, and plaques start to form in the healing clots lining your arteries. Having plaques does not cause a heart attack; a heart attack occurs only after a plaque breaks off from the arterial wall. Then the damaged area bleeds and clots. The clot that forms in the place where the plaque broke off grows to block the blood flow to the heart. The part of the heart muscle that has had its blood supply shut off dies and you suffer a heart attack.
Since omega-3 fatty acids reduce clotting, they can help to prevent heart attacks. They also reduce inflammation, the process that first punches holes in arteries to start the formation of plaques. The Food and Drug Administration has approved some fish oil pills to treat high triglycerides, another risk factor for heart attacks. However, at this point, fish oil pills have not been shown to prevent heart attacks.
• Eating fish up to twice a week appears to reduce risk for heart attacks.
• Taking fish oil pills has not been shown to prevent heart attacks.
• It is possible that scientists may have failed to show that fish oil pills help to prevent heart attacks because many of the supplements are broken down into oxidized fats whose harm equals or exceeds any benefits the pills may offer.
• If you choose to take fish oil pills, break open a capsule from each bottle you buy. If it smells or tastes rancid, discard the bottle or return it to the store.