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Fish Oil Pills Have Not Been Shown to Prevent Heart Attacks

Studies show that neither taking omega-3 polyunsaturated fatty acids (PUFAs) in fish oil pills nor eating fish reduce the risk for heart attacks (American Journal of Preventive Medicine, September 16, 2016). A review of studies in the world's scientific literature agrees that taking fish oil pills does not prevent heart attacks (Am J Clin Nutr, Sept 14, 2016;104(4):951-952). Yet more people are taking fish oil pills than ever before. In 1999, 1.3 percent of North Americans took fish oil pills and by 2012 the number had gone up to 12 percent (JAMA, Oct 11, 2016;316(14):1464-1474). North Americans are now spending more than $1.1 billion on fish oil pills per year.

Data from the many studies on fish oil pills has failed to show that they help to prevent heart attacks. From 2005 to 2012, at least two dozen rigorous studies of fish oil pills were published and 22 showed no benefit at all in preventing heart attacks or strokes in high-risk populations -- obese, low exercise, meat eaters, smokers, history of heart disease, high cholesterol, hypertension or Type 2 diabetics (JAMA Intern Med, 2014;174(3):460-462). A clinical trial of 12,000 people, done by Dr. Gianni Tognoni, found that fish oil pills did not reduce the rates of death from heart attacks or strokes (N Engl J Med, May 9, 2013; 368:1800-1808).

Why So Many People Believe that Fish Oil Pills Prevent Heart Attacks
Many older studies have shown an association between eating fish and reduced rate of heart attacks, but the overwhelming majority of the more recent studies have failed to show that eating fish prevents heart attacks, strokes or premature death. In the 1970s, Danish scientists Dr. Hans Olaf Bang and Dr. Jorn Dyerberg reported that the Inuits living in Greenland had low rates of heart attacks and ate a lot of fish. Later a University of Ottawa cardiologist, George Fodor, showed that the Inuits had the same heart disease rate as other populations. That didn't stop the American Heart Association from listing fish oils as a way to reduce heart attack risk.

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, researchers believed that they could help to prevent heart attacks. They could also reduce inflammation, the process that first punches holes in arteries to start the formation of plaques. The Food and Drug Administration has approved fish oil pills as a treatment for high triglycerides, which are a risk factor for heart attacks. However, at this point, fish oil pills have not been shown to prevent heart attacks by these mechanisms or any other way.

• A study of more than 12,000 people showed that a gram of fish oil daily did not help to 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).

• The Iowa Women's Health Study found no significant association between fish or fish oil and prevention of heart attacks (Am J Epidemiol, 2004; 160:1005-1010) or strokes (Stroke 2011; 42:3621-23).

• Several studies show that eating fish is associated with reduced risk for heart attacks, but this does not show that eating fish prevents heart attacks. It could be that people who eat fish eat less red meat, which is a known heart attack risk factor.

Fish Oil Pills Are Not Harmless
Fish oil in pills is extracted from oily fish such as sardines, anchovies, herring, mackerel, salmon and tuna. During processing, the oil is exposed to air, which means that the oil can become oxidized. 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 harmless; it becomes harmful only after the fats in it are oxidized to form oxidized LDL cholesterol. See Cholesterol and Oxycholesterol

The omega-3 fatty acids in fish oils 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 exceeded 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 that scientific studies 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 you should throw the bottle away. Even if you buy a brand that you trust, check each bottle because one batch can be fresh while the next batch can be rancid.

A study this month showed that rancid fish oil pills may cause diabetes (Am J Physiol - Reg Int and Comp Physiol, September 1, 2016;311(3): R497-R504). Pregnant rats were fed water or rancid fish oils until they gave birth. The newborn rats from the mothers that were fed rancid fish oils had higher blood sugar levels and reduced response to insulin, and had a much higher death rate after birth.

My Recommendations
• I do NOT recommend taking fish oil pills.
• There is no proven benefit from taking fish oil pills and there may be some harm. On the other hand, some studies show benefit from eating fish once or twice a week, and eating fish has not been shown to be harmful (even with the possible issue of mercury or other contamination). However, no one has shown benefit from eating fish more often than twice a week.
• If you do decide to take fish oil, prescription pills are preferable to those sold over the counter because there is a higher level of quality control for the prescription products.
• Whether your pills are by prescription or over the counter, with every new bottle, take out a pill, cut it open and smell it. If the pill smells fishy, it is rancid and you should throw the whole bottle away. See Check those Fish Oil Pills

Checked 11/19/17

October 30th, 2016
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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