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Something Fishy: Fish Oil Supplements

Matthew Crowley

Skeptical Briefs Volume 27.3, Fall 2017

Fish oil supplements are immensely popular these days. According to the New York Times, 10 percent of Americans consume fish oil supplements regularly. In the United States, fish oil supplements accounted for $1.2 billion in sales for the year 2014. Most commonly people take these supplements for cardiac health, but many claims have been made for benefits besides protection of the heart. Claims for substances that act as panaceas are familiar to skeptics. Skeptics may take interest in the variety and boldness of claims made for fish oil supplements—particularly since fish oil is not a “miracle drug” but a nutritional supplement.

Conditions for which fish oil supplements have been claimed to be helpful include cardiovascular disease, depression, anxiety, seasonal affective disorder, postpartum depression, bipolar disorder, ADHD, Alzheimer’s disease, arthritis, cancer, eczema, psoriasis, sunburn, diabetes, eye disorders, polycystic ovarian syndrome, and endometriosis. They have also been claimed to help increase a child’s intelligence and help people achieve weight loss. Clearly an extensive analysis of all these claims is beyond the scope of this article, yet a summary is still possible.

Where do we begin? How did fish oil supplements become so popular in the first place? First off, “fish oil supplements” should be disambiguated from cod liver oil, which has long been used as a source of vitamins A and D. The fish oil under consideration here contains high amounts of omega-3 fatty acids, primarily DHA (docosahexanoic acid) and EPA (eicosahexanoic acid), not vitamins A and D. Omega-3 fatty acids are like vitamins and minerals in that they are required for human nutrition and can’t be manufactured by the body. They are considered “essential fatty acids.” The designation “omega” refers to one end of the fatty acid molecule, and the “3” indicates a double bond three carbon atoms away from that end. Unlike other fats, these molecules are not “burned” for caloric fuel but function to modulate biochemical processes such as inflammation.

The current fascination with these molecules largely began in the 1970s, when two Danish researchers—Bang and Dyerberg—began investigating Inuit Eskimos living in Greenland. They wanted to understand the consequences of this unique population eating so much fat. The Inuit’s diet consisted “mostly of meat of whales, seals, sea birds, and fish” according to the researchers. Bang and Dyerberg suspected that the omega-3 oils in the fish they ate acted to protect against cardiac disease, which would be expected to result from a diet rich in saturated animal fat. Bang and Dyerberg were clinical chemists, not epidemiologists, yet their research was epidemiological in nature as they analyzed records maintained by Greenland’s chief medical officer. In addition, they drew blood from 130 natives of the small town of Uummannaq. Compared to their control population of Danes, the Inuit had lower levels of triglycerides and cholesterol, as well as higher levels of omega-3 fatty acids. Bang and Dyerberg published their findings in 1971 in the British journal The Lancet, one of the preeminent medical journals in the world. By 1980, they began to publicly suggest that omega-3 fatty acids in the diet might help prevent cardiac disease in populations besides the Inuit.

According to George Fodor, a cardiologist at the University of Ottawa Heart Institute, the number of individuals that died of cardiac disease may have been significantly underrepresented in the Lancet study. Since this was a remote area, with people living far from urbanized medical centers, the exact cause of death may have not been precisely determined. In any event, this was the birth of the meme that fish oils may help prevent cardiac disease. Since that time, a wide variety of studies have been done regarding heart health. It’s fairly well established that fish oils can lower LDL or “bad” triglyceride levels, which is a valid risk indicator for heart disease.

In fact, the FDA has approved several drugs, including Lovaza and Vascepa, which are semi-synthetic versions of fish oil, meaning that the natural fatty acid has been slightly chemically modified. These drugs are indicated for people with very high levels of blood lipids. In addition, fish oil has an anticoagulant effect, much like aspirin, that may reduce the risk of blood clots.

The problem is that a “risk indicator” is not the same as the risk itself. The important question is whether fish oil supplements actually lower risk of cardiac disease, not just bad triglyceride levels. Between 2005 and 2012, at least two dozen large scale studies of fish oil were conducted in high-risk populations. All but two found no benefit, including one published in the New England Journal of Medicine, which included 12,000 people. The evidence simply doesn’t support the claim that fish oil supplements can reduce the risk of cardiac disease, at least in high-risk individuals.

What about other claims for fish oil supplements, besides amelioration of cardiac disease? Perhaps the most encouraging findings are those related to rheumatoid arthritis. Essential fatty acids within fish oil act as anti-inflammatories by blocking the action of prostaglandins and cytokines. Multiple studies have demonstrated significant pain relief for rheumatoid arthritis sufferers, in some cases enabling individuals to completely discontinue use of conventional non-steroidal anti-inflammatory drugs.

Fish oil supplementation has also been studied for its potential to prevent dementia in the elderly. Study findings have been mixed, some suggesting benefit while others show no benefit. Thus, unambiguous evidence that fish oil can prevent the onset of dementia is lacking. If there is a silver lining to this unfortunate state of affairs, it’s that studies of longer duration should be undertaken in order to observe greater mental changes in study participants. It’s possible that positive benefits of fish oil may appear over greater time spans.

An interesting set of claims surrounds the use of fish oil for exercise recovery. The idea is that exercise induces some degree of inflammation and oxidation in the body, and fish oil can help suppress these negative processes. There are studies that support this. Even more suggestive is the claim from a popular bodybuilding website, Bodybuilding.com, that fish oil can help add muscle mass: “Perhaps more interesting for people looking to build muscle, EPA and DHA supplementation has been suggested to support muscle protein synthesis and limit muscle protein degradation. This can mean less muscle breakdown and more muscle growth.” Note this claim hinges on the word suggestive. Indeed, a number of studies point in the direction of fish oil having at least some positive impact on muscle building for those who exercise. It should be noted that how positive an effect is often not overtly stated and only inferred.

The story of fish oil is not unusual. There are many drugs and nutritional supplements for which the evidence of efficacy is marginal or for which the effect is minimal. For most people, the choice to buy and consume fish oil is a simple binary; Should I take this? Yes or no? If I spend money on this supplement, will it provide a benefit commensurate with the money spent? The bulk of studies for a wide range of conditions indicate either no effect or a mildly positive effect. In many cases, the evidence is “suggestive,” which really means there is a physiological mechanism why fish oil could work. The exception seems to be rheumatoid arthritis, for which the evidence of benefit is fairly compelling. Unless one is on anticoagulant drugs, introduction of fish oil supplements to the diet has not been shown to be negative and may provide a positive benefit for a variety of conditions, though this benefit is likely mild. A decision to supplement one’s diet with fish oil is therefore reasonable, though ironically not for what many people take it for, which is prevention of cardiac disease.