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The Truth About Fish Oil Supplements: Benefits, Risks, and Controversies

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The Truth About Fish Oil Supplements: Benefits, Risks, and Controversies

Fish oil, widely promoted for its health benefits, is seldom criticized in mainstream media or the health community.

Touted for its high concentration of heart-healthy and inflammation-reducing omega-3 fatty acids, fish oil supplements are commonly seen on the shelves of drug stores and in people’s medicine cabinets.

According to data from the National Health Interview Survey, fish oil supplements are the most popular non-vitamin or mineral natural product consumed by both adults and children as a dietary supplement.1

The survey found that 18.8 million adults (nearly 8%) and 664,000 children (over 1%) ages 4 to 17 had taken a fish oil supplement in the previous month.

The ubiquitous dietary supplement is also backed by a massive industry, with recent data indicating that there is a high demand for the product. By 2033, experts estimate the market value of the fish oil industry to hit a whopping 34.4 billion dollars.2

Yet, despite fish oil’s aggressive promotion by the industry, there is growing evidence highlighting its potential dangers. There is also limited support for its use as a functional or preventative medicine.


Fish Oil History and Use

Fish oil is one of the earliest substances to be marketed and sold as a dietary supplement.

In the late 1800s, fish oil in the form of cod liver oil was used to treat physical and mental disorders of the time, such as tuberculosis and hysteria3.

Today, fish oil supplements are taken orally in the form of capsules or soft gels. The oil is usually extracted from fatty fish such as salmon, herring, mackerel, or sardines. Other popular formulations are derived from krill or cod liver.

Fish oil contains two important kinds of key omega-3 fatty acids: EPA and DHA. These fatty acids are said to have an anti-inflammatory effect in the body. They also are purported to exert a triglyceride-lowering and blood pressure-lowering effect, which explains their promotion as a cardiovascular-supporting substance4

Because of this, the US National Institute of Health (NIH) recommends that adults consume at least 250 mg of EPA and DHA per day.5

The American Heart Association (AHA) also issued guidelines recommending 1 gram of fish oil daily for prevention of cardiovascular incidents. However, the AHA recommended consuming whole fish rather than extracted oil.

In contrast to these health organizations, in the UK, the NIH did not recommend the use of fish oil or omega-3 supplements for prevention of cardiovascular disease due to their “inconclusive benefits.”

The Controversy Surrounding Fish Oil

Fish oil supplements are one of the most controversial topics in the health industry due to

their debated health claims, conflicting research, and concerns over manufacturing quality. 

The common argument that fish oil helps prevent heart disease is primarily based on its

ability to lower blood lipids, a continuation of the American Heart Association’s “traditional heart protective diet” approach.6

However, this argument is undermined by findings that the reduction in blood triglycerides results from fish oil's harmful effects on the liver.7

Studies with rats, for example, have shown that EPA and DHA only reduce blood lipids when the rats were fed, leading to the fats being stored into tissues and causing a subsequent suppression of mitochondrial respiration.8

Another argument for consuming fish oil and omega-3 fats is the idea that diseases are linked to lower levels of EPA, DHA, or arachidonic acid in the body, suggesting that these oils are deficient and this deficiency causes the disease. 

However, these oils are very prone to oxidation and tend to break down quickly when tissues are injured, stressed, exposed to toxins, radiation, or even light. This tendency to oxidize is what makes them useful in products like varnish or paint. However, it also means they make tissues more vulnerable to damage.

Often, it is the presence of these oils, not their absence, that leads to disease. This is due to the oxidative stress caused by lipid breakdowns. Since oxidation in the body is a trigger for inflammation, oxidized fatty acids from fish oils could hypothetically lead to arterial damage and atherosclerosis.

EPA and DHA are not only sensitive to oxidation in the body, but quickly oxidize throughout their processing. This causes a tendency for the oils to turn rancid while sitting on the shelves, which may cause further detrimental health effects to consumers.

For instance, a study in the Journal of Nutritional Science by Jackowski et al. evaluated oxidation levels in over-the-counter fish oils available in retail stores in Canada and obtained some interesting results.

The study comprised a total of 171 supplements from forty-nine brands. Shockingly, half of the brands showed a significant level of oxidation, with 39 percent exceeding the international safety recommendations for total oxidation value. 

Meanwhile, in the USA, dangerous levels of lipid peroxides were discovered in 27 percent of similar products tested. This trend was also found in other countries as well. 

It is important to note that the level of oxidation varies depending on the methods of oil extraction, the type of processing, encapsulation, storage, and modes of transport. 

Due to a lack of evidence, the safety and health effects of eating rancid or oxidized fish oil is currently unknown.

However, a study done on mice found that long-term intake of fish oil led to reduced cellular function, an increase in oxidative stress, increased aging, and a shorter lifespan.9

Quality control of supplement brands is a separate issue that deserves its own topic. However, when it comes to products that easily spoil, such as fish oil, it is important to be careful when choosing brands and to perform due diligence.

Eating a whole, fresh fish may also be a healthy alternative to supplements if one cannot verify the quality of a certain product.

Recent Studies Cast Doubt on Fish Oil Claims

A recent meta-analysis study published in BMJ Medicine has generated headlines after it contradicted the notion that fish oil supplements are cardioprotective.

A team of researchers in China tracked over 400,000 participants from the UK Biobank, a biomedical database, for an average of 12 years to examine the effects of fish oil supplements on the development of heart conditions like atrial fibrillation (irregular heartbeat), heart attack, stroke, and heart failure. 

They also investigated whether these supplements influenced the progression of existing heart conditions.

The findings revealed that regular use of fish oil supplements was linked to a 13% increased risk of developing atrial fibrillation and a 5% increased risk of having a stroke. However, the study also found that these supplements were associated with a 15% lower risk of progressing from atrial fibrillation to a heart attack and a 9% lower risk of progressing from heart failure to death.

Thus, the findings are somewhat contradictory, as they suggest, on the one hand, that fish oil is cardiotoxic for those without heart disease but helpful in those who have already been diagnosed with cardiovascular disease or have had a previous stroke or heart attack.

It is also important to note that this study focused solely on omega-3 supplements and did not provide information on the risks and benefits of consuming oily fish.

Another previous study published in the Cochrane Library, as well as several others, also failed to find any significant beneficial effect on all-cause mortality or cardiovascular risk from consuming omega-3 supplements.

The role of omega-3 supplements like fish oil on diseases such as prostate cancer, dementia, or Crohn’s disease is limited at best.

Should You Stop Taking Fish Oil?

Omega-3s are essential fatty acids crucial for health, as your body cannot produce them and they must be obtained through diet. 

According to Tom Sanders, a professor emeritus of nutrition and dietetics at King’s College London, small amounts of long-chain omega-3 fatty acids support a healthy heart and normal brain and visual development.

However, Sanders said that most trials on heart disease prevention have involved people with type 2 diabetes or those who have already experienced a cardiovascular event. Additionally, while high doses of fish oil supplements have been linked to reduced cardiovascular mortality, most studies using lower doses do not show the same benefit.

“Current guidelines for cardiovascular disease prevention recommend eating fish but not taking fish oil supplements,” he told The Guardian.

Clinical nutritionist Nathan Davies of the University College London also advised eating whole fish rather than taking supplements.

“Eating a healthy diet is always preferable to taking supplements, and following NHS advice to eat oily fish weekly is beneficial for omega-3 intake, vitamin D, and other micronutrients,” he said.


Key Takeaways 

  • Fish oil is widely promoted for its health benefits, especially its high concentration of heart-healthy omega-3 fatty acids.
  • Health organizations like the NIH and AAA have recommended the consumption of EPA and DHA, though guidelines vary on whether to use supplements or whole fish.
  • Omega-3 oils are prone to oxidation, which can make them less effective and potentially harmful if consumed in an oxidized state.
  • Recent research suggests fish oil supplements may increase the risk of atrial fibrillation and stroke but could reduce the progression of heart disease in those already affected.
  • There is no substantial evidence supporting the use of omega-3 supplements for preventing other diseases 
  • Experts recommend eating a healthy, varied diet with oily fish rather than relying on supplements, as this is beneficial for omega-3 intake and overall nutrition.
  • People should consult healthcare providers for personalized advice and avoid self-medicating with supplements.
The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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  1. Trends in the use of complementary health approaches among adults: United States, 2002-2012. (2015, February 10). PubMed. ; Use of complementary health approaches among children aged 4-17 years in the United States: National Health Interview Survey, 2007-2012. PubMed. Published February 10, 2015.
  2. MarketResearch.Biz. Fish Oil Market Booms, to be Valued at USD 34.4 Bn by 2033, Growing at 7.10% CAGR by 2033, Asia-Pacific to be Dominant Region | GlobeNewswire News Room. Published January 24, 2024.
  3. Science History Institute. The Man with a Fish on His Back | Science History Institute. Science History Institute. Published June 1, 2023.
  4. Office of Dietary Supplements - Omega-3 fatty acids.; Skulas-Ray AC, Wilson PWF, Harris WS, et al. Omega-3 Fatty Acids for the Management of Hypertriglyceridemia: A Science Advisory From the American Heart Association. Circulation. 2019;140(12). doi:10.1161/cir.0000000000000709
  5. Office of Dietary Supplements - Omega-3 fatty acids.
  6. The American Heart Association Diet and Lifestyle recommendations. Published December 18, 2023.
  7. Hagve T a., Christophersen BO. Mechanisms for the serum lipid-lowering effect of n-3 fatty acids. Scandinavian Journal of Clinical and Laboratory Investigation. 1988;48(8):813-816. doi:10.3109/00365518809088765; Ritskes-Hoitinga J, Verschuren PM, Meijer GW, et al. The Association of Increasing dietary concentrations of fish oil with hepatotoxic effects and a higher degree of aorta atherosclerosis in the ad lib.-fed rabbit. Food and Chemical Toxicology. 1998;36(8):663-672. doi:10.1016/s0278-6915(98)00028-3
  8. Osmundsen H, Braud H, Beauseigneur F, Gresti J, Tsoko M, Clouet P. Effects of dietary treatment of rats with eicosapentaenoic acid or docosahexaenoic acid on hepatic lipid metabolism. Biochemical Journal. 1998;331(1):153-160. doi:10.1042/bj3310153
  9. Tsuduki T, Honma T, Nakagawa K, Ikeda I, Miyazawa T. Long-term intake of fish oil increases oxidative stress and decreases lifespan in senescence-accelerated mice. Nutrition. 2011;27(3):334-337. doi:10.1016/j.nut.2010.05.017
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