Omega-3 supplements have little effect on cardiovascular disease and mortality


Last updated on November 15th, 2022 at 12:05 pm

This article about omega-3 supplements is a companion piece to my recent article about fatty fish and cardiovascular disease. There is little evidence that two servings of fatty fish, which are filled with omega-3, have any effect on the risk of cardiovascular diseases.

I have been skeptical of supplements for a long period of time. Supplements are generally of low quality, they don’t prevent or cure cancer, they don’t prevent colds, they can’t boost the immune system, and they don’t prevent heart disease. Now there is a powerful review of omega-3 supplements that shows that it has little effect on cardiovascular disease.

Unless one has a chronic disease or is chronically malnourished, there are precious few instances where supplements are necessary. A couple of cases where supplements may be critical include prenatal folic acid supplements to prevent neurological defects in the developing fetus, vitamin C to prevent scurvy, and vitamin D supplements for individuals who do not produce enough endogenous vitamin D. In each of these cases, however, supplements are necessary to counteract a micronutrient deficiency that results from a chronic deficiency in the diet.

The benefits of omega-3 supplements have always been intriguing to me because it is one supplement that I thought might be useful for improving cardiovascular health based on some clinical evidence. But as I reviewed before, the evidence seemed awfully weak. With this new study, there may be no evidence whatsoever supporting the use of omega-3 supplements, at least for cardiovascular disease.

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What are omega-3 supplements?

Omega-3 fatty acids, which are the primary ingredients in these supplements, are generally found in fish, as it is produced by the phytoplankton that is the primary food source of much of the prey for larger fish and bio-accumulates up the food chain. However, for humans, there are other sources of omega-3 oils including walnuts and edible seeds, eggs (especially those from chickens who are fed extra omega-3 supplements), and other non-fish sources.

Omega-3 fatty acids are considered one of the “essential fatty acids” because they are important to normal growth in young children and animals, and because humans (and many other mammals) cannot biochemically manufacture omega-3 fatty acids. Generally, humans consume adequate amounts of fatty acids and only rarely are required to take omega-3 supplements to maintain proper health.

Now for some science.

There are three principal omega-3 fatty acids — alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). The main sources of ALA in the U.S. diet are vegetable oils, particularly canola and soybean oils. ALA can be converted, usually in small amounts, into EPA and DHA in the body. EPA and DHA are found in seafood, including fatty fish (trout, salmon, and tuna) and shellfish (including crabs, lobsters, clams, and mussels).

Without getting into a lot of complex biochemistry, omega-3 oils are converted by various organs into key agents that are necessary for physiological development and for regulating some aspects of the immune response. For example, omega-3 fatty acids are converted by enzymes into what is now known as eicosanoidsthromboxanesprostacyclins, and leukotrienes. Eicosanoids, which have numerous biological functions such as wound repair, typically have a short lifespan in the blood — they are quickly metabolized by enzymes. However, if the rate of synthesis exceeds the rate of metabolism, the excess eicosanoids may be dangerous.

As I keep saying, the immune system is not some pathetic network in the body — it is quite robust and can only be damaged through chronic disease or malnutrition. A normal diet that includes fatty acids is more than sufficient to keep that part of the immune system running very well. It does not mean that taking omega-3 supplements will cause your immune system to be even better. You cannot boost your immune system.

Additionally, omega-3 fatty acids are important for a number of bodily functions, including muscle activity, blood clotting, digestion, fertility, and cell division and growth. Specifically, DHA is important for brain development and function.

Once again, just because a little bit of omega 3 in the diet may be good, it’s possible that excess amounts may not be. One of the major myths of the supplement industry is that “if a little is good, a lot is better.” There is an assumption that the body is so weak that it constantly needs to be given omega-3 fatty acids or any other supplement to survive. Well, that’s just not supported by science.

Why did omega-3 supplements become a thing?

Observational studies done in the late 1980s seem to indicate relatively low death rates due to cardiovascular disease in Inuit populations with high seafood consumption. These results began the rush to consume omega-3 supplements and created a booming supplement industry for the product. A lot of researchers began to critique these studies because confounding factors may have been as important as the fatty acids themselves.

Since the publication of those initial studies, much research has been done on seafood and heart disease. And the results don’t give much credence to the cardiovascular benefits of omega-3 fish oils as a useful supplement.

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Are there benefits of omega-3 supplements?

There are some very specific benefits of omega-3 supplements that are supported by strong scientific evidence.

  1. Infant development — Omega-3 supplements, especially in the form of DHA, might be important for young children. The nutritional value of seafood is particularly important during early development. The Dietary Guidelines recommend that women who are pregnant or breastfeeding consume at least 8 ounces but no more than 12 ounces of seafood each week and not eat certain types of seafood that are high in methylmercury — a toxin that can harm the nervous system of a fetus or young child. However, the recommendation includes consuming seafood, not omega-3 supplements, although if one is afraid of consuming seafood, it is useful in this case.
  2. Rheumatoid arthritis  — A 2012 systematic review concluded that the types of omega-3s found in seafood and fish oil may be modestly helpful in relieving symptoms of rheumatoid arthritis. The review of 23 studies concluded that “a fairly consistent, but modest, benefit of (omega 3 fish oils) on joint swelling and pain, duration of morning stiffness, global assessments of pain and disease activity, and use of non-steroidal anti-inflammatory drugs.” The benefits are just on the border of clinically significant, and will not reverse the course of the disease, but it may be helpful.
  3. Other claims — Omega 3 fish oil supplements also have been claimed to prevent or treat other conditions–allergies (meta-review says no), asthma (research says no), Crohn’s disease (ineffective), cystic fibrosis (no useful clinical data according to meta-review), kidney disease (no solid clinical evidence), lupus (no evidence), obesity (no evidence), osteoporosis (no conclusive clinical evidence), and ulcerative colitis (no evidence).

In general, omega-3 supplements, even ones rich in EPA and DHA, may not help prevent or manage health conditions. In fact, more omega-3 fatty acids may not be better.

Moreover, some of the benefits of consuming seafood high in omega-3 fatty acids may result from people eating it in lieu of other, less healthful, foods. The so-called Mediterranean diet is an example of a high fish diet that may be linked to better cardiovascular outcomes.

In general, there is no conclusive or, in some cases, negative evidence regarding the benefits of omega-3 fish oil for most health conditions. In fact, even the annoying and wasteful National Center for Complementary and Integrative Health, which pushes junk medicine under the guise of the National Institutes of Health, provides a fairly negative review of the benefits of omega-3 fish oil.

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Omega-3 supplements and cardiovascular disease

Many individuals take omega-3 supplements to prevent heart disease. But what does the science say after nearly 30 years since that initial epidemiological study was done with Inuit populations?

There have been several studies that have evaluated the potential benefits of omega-3 fish oil supplements, which are rich in EPA and DHA, on heart disease risk. These studies compared the number of cardiovascular events (such as heart attacks or strokes) or the number of deaths in people who were given the supplements with those in people who were given placebos or standard cardiovascular care.

The results of individual studies were inconsistent with a range of results from clinically useless to somewhat useful. In 2012, two separate meta-analyses (the best kind of evidence available) of these studies were published – the first one analyzed only those studies which included individuals with a history of heart disease, and the other one analyzed studies of individuals both with and without a history of heart disease. Neither meta-analysis found convincing evidence of protective benefits for omega 3 fish oil supplementation.

A new systematic review (considered the pinnacle of the hierarchy of biomedical research), published in the Cochrane Database of Systematic Reviews, seems to indicate that there isn’t much value in omega-3 supplements for preventing cardiovascular disease. The study included 79 randomized controlled trials that lasted greater than 12 months. Over 112,000 patients were included in these studies. In addition, the study participants were from  Asia, Europe, North America, and Australia.

The study showed no effect of omega-3 supplements on the following cardiovascular outcomes:

  • All-cause mortality, risk ratio (RR, see Note 1) of 0.98.
  • Cardiovascular mortality, RR = 0.95.
  • Cardiovascular events (stroke, heart attack, and other related events), RR=0.99.
  • Coronary heart disease mortality, RR=0.93.
  • Stroke, RR=1.06.
  • Atrial fibrillation, RR=1.06.

Omega-3 supplements that contain ALA also had little effect except for minor risk reduction in three cases:

  • Possible reduction in cardiovascular event rates.
  • A 9% relative reduction in coronary heart disease mortality.
  • A 33% relative reduction in arrhythmias.

However, in each case, the absolute reduction was relatively small, and the quality of the studies that showed this possible reduction was of low-quality.

The authors concluded that:

This is the most extensive systematic assessment of effects of omega-3 fats on cardiovascular health to date. Moderate- and high-quality evidence suggests that increasing EPA and DHA has little or no effect on mortality or cardiovascular health (evidence mainly from supplement trials). Previous suggestions of benefits from EPA and DHA supplements appear to spring from trials with higher risk of bias. Low-quality evidence suggests ALA may slightly reduce CVD event risk, CHD mortality and arrhythmia.

Overall, this powerful review did not provide robust evidence that omega-3 supplements have an important effect on cardiovascular events. If you are taking these fatty acids because you think they’re going to protect you against heart attacks, this robust evidence says that it’s a waste of money.

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New studies

An updated systematic review from Cochrane examined 86 randomized clinical trials (with 162,796 participants) and found no benefit from omega-3 fatty acids. The authors actually found that omega-3 fatty acids may increase the risk of cardiovascular mortality and events.

The Skeptical Cardiologist reviewed some large clinical trials of omega-3 fatty acids, and he concluded:

For the remainder of the presentation I spoke without script, analyzing in detail recent large randomized controlled trials of large dosage omega-3 fish oil supplementation. Spoiler alert, the STRENGTH trial found no cardiovascular benefits.

Along the way I touch on the weaknesses of observational epidemiology and the sneaky ways the fish oil supplement industry biases scientific publications.

My conclusion is that there is no compelling evidence for you to take over the counter fish oil supplements for primary or secondary prevention of cardiovascular disease.

One reason to not use omega-3 supplements

Most omega-3 fish oils are processed from one type of fish — menhaden, which is a key part of the food chain in the ocean. The highly oily fish (which gives us the omega 3 fatty acids) consumes and redistributes a significant amount of energy within and between the Chesapeake Bay and other estuaries, and the coastal ocean (see The Most Important Fish in the Sea: Menhaden and America). Menhaden are not generally eaten by humans, although they had an important role in fertilizing crops in early America.

The problem has become that fish oil processors harvest over 500 million menhaden a year, and this has caused a drop in the population of these fish. Because they are an invaluable prey species for predatory fish (which are also important game and commercial fishes) such as striped bass, bluefish, mackerel, flounder, tuna, and sharks. They are also a critical food source for many avian species including egrets, ospreys, seagulls, northern gannets, pelicans, and herons.

In 2012 the Atlantic States Marine Fisheries Commission declared that the menhaden stocks had become depleted because of overfishing, almost all of which was used to manufacture omega 3 supplements for people who consume them with few health benefits. Some important predator species populations have crashed due to the lack of menhaden on which they could feed.

So if you believe that taking your supplements may help you, and think that it does no harm — well, you may be destroying our environment.

Summary

Like with nearly every supplement I’ve examined, the claimed benefits of omega-3 supplements far exceed what is shown by the actual clinical evidence. There is some evidence that omega-3 supplements may be slightly beneficial in a few conditions, but an adequate diet probably negates the need for the supplement even there.

And as for the use of omega-3 supplements in preventing cardiovascular disease, there are better choices – like statins, where powerful systematic reviews have shown that they actually do improve cardiovascular outcomes.

The short summary is that you shouldn’t waste your money on omega-3 supplements.

Notes

  1. A risk ratio measures the relative risk of a particular outcome between an experimental group and a control group. A number greater than 1.0 implies that the experimental group has a higher risk of an outcome compared to the control. A number less than 1.0 implies the experimental group has a lower risk than the control. Any number that is statistically equivalent to 1.0 means there’s no difference between the groups. Thus, an RR = 0.98 means that the omega-3 supplement group shows almost no difference in risk of all-cause mortality than the control group.

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