Fish Oil: Chasing Evidence to Tip the Scales


Millions of Americans take fish oil supplements every day in hopes of preventing heart disease, depression, and even premature birth. It is one of the most popular nutritional supplements in the US

There has been a lot of research on fish oil supplements, but questions remain about their benefits.

Many studies so far indicate that the dietary supplements do not offer the benefits that marketers are promoting. A recent large, randomized clinical trial found that fish oil at a dosage found in many supplements did not reduce the incidence of heart disease or cancer, the main benefits it is associated with.

However, scientists are continuing to investigate the potential heart health effects, including some other results from the most recent large study. They also delve deeper into possible effects that have been less well studied: on depression, cognition, autism, and other disorders.

“The judges really haven’t decided yet,” says Joann Manson, director of preventive medicine at Harvard-affiliated Brigham and Women’s Hospital, who led the latest study on fish oil and heart health and cancer.

Despite the debate, sales of fish oil supplements rose 1.8% to approximately $ 1.2 billion in 2017, according to the Nutrition Business Journal.

The key components of fish oil, two polyunsaturated fatty acids called eicosapentaenoic acid, or EPA, and docosahexaenoic acid, or DHA, are designed to be present in cell membranes throughout the body. Although these fatty acids are essential for cell function, the human body has difficulty producing them and has to get them from food. EPA and DHA are found in high amounts in oily fish such as salmon.

In the 1970s, researchers discovered that Inuit, whose diet consisted primarily of the fish they caught in the ocean, had low rates of cardiovascular problems. This finding led to thousands of studies on the potential benefits of omega-3 fatty acids, a recommendation by the American Heart Association that people eat fish at least twice a week to prevent heart disease, and an industry of fish oil supplement manufacturers.

Today the recommendation is to eat more fish. But with fish oil supplements “you haven’t yet been able to reproduce these benefits,” says Craig Hopp, assistant director of the division of extramural research at the National Center for Complementary and Integrative Health, a branch of the National Institutes of Health that conducts scientific research into health practices and – products outside of conventional medicine are financed. The NCCIH is currently funding studies investigating whether omega-3 fatty acids may increase the effects of antidepressants, reduce inflammation, and help children with autism spectrum disorder.

The problem is the same when trying to reproduce the benefits of fruits and vegetables with vitamins or supplements, he says. Trying to understand exactly what “is responsible for these benefits” in a diet, he says, noting that “it is probably not just a thing”.

Researchers have identified several benefits. High doses of fish oil can reduce triglycerides, a type of fat in the blood that can increase your risk of heart disease. Some patients with high triglycerides take prescription drugs that have different dosages and ingredients than over-the-counter supplements.

A recent research review found that increased intake of omega-3 fatty acids, especially EPA and DHA, reduced the risk of premature birth – a finding that fish oil supplements could give a boost as many pregnant women worry about contamination in fish, says Duffy MacKay, Senior Vice President of Scientific and Regulatory Affairs at the Council for Responsible Nutrition, a trade association that represents manufacturers of nutritional supplements. (Industry standards set limits for contaminants like heavy metals in fish oil supplements and how they can be tested and filtered out, he says.)

Ultimate Omega from Nordic Naturals.


Nordic naturals

Dr. Manson-led study, funded by multiple NIH institutes, that followed 25,871 men over 50 and women over 55 for more than five years found that one gram of fish oil per day did not reduce the risk of heart disease or invasive cancer. However, researchers also found a 28% lower risk of heart attack in participants who took fish oil. The benefit was even greater – a 40% reduction – for participants who took fish oil and ate less than 1.5 servings of fish per week.

The results were secondary to the study’s central focus and need further investigation, warns Dr. Manson. Still, she says, “We believe there is a promising signal of cardiac health benefit.”

“There are tempting indications that there might be something,” says Pieter Cohen, an associate professor at Harvard Medical School and the Cambridge Health Alliance who studies dietary supplements. He says they should be studied further, but should also be seen in the context of many previous studies that showed no benefit for heart disease. “If someone comes up to me and says I’m worried about not having enough omega-3s, I’d rather eat fish than take supplements,” he says.

The knowledge that omega-3 fatty acids can prevent premature births should also be treated with caution, he says. “The ideal would be to follow these women and their babies so we can have more information,” he says.

Using data from the same large study led by Dr. Manson, researchers are analyzing the effects of fish oil treatment on depression, cognition, diabetes, chronic pain, and other conditions, says Dr. Manson. Results are expected in the next six months to a year, she says.

Olivia Okereke, director of geriatric psychiatry at Massachusetts General Hospital who leads analysis of depression, hopes she will provide answers that previous, smaller, and shorter observational studies failed to provide. The researchers analyze participant data for diagnosing depression, as well as self-reported mood symptoms and how they differ over time, she says.

The Alpha and Omega 3 on Fish Oil Supplements

The judges are not yet sure whether fish oil supplements have benefits for a variety of health conditions. There are a few things you should know about any dietary supplement.

  • Check how much eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) a dietary supplement contains. These are the long chain omega-3 fatty acids that are the key components in a fish oil supplement. Avoid products that don’t state how much EPA and DHA they contain.
  • There is no government recommended daily value. The US dietary guidelines recommend eating seafood in amounts equivalent to 250 milligrams of EPA and DHA per day. The Food and Drug Administration says dietary supplement labels should recommend no more than 2 grams of EPA and DHA daily, although doctors may prescribe more for patients who need to lower their triglycerides. Everyone has different needs, so speak to your doctor. You can get a blood test to see how much EPA and DHA are in your blood.
  • Fish oil supplements shouldn’t smell or taste fishy. High quality fish oil is processed in such a way that oxidation is prevented, which causes the fats to break down and smell.
  • Side effects of taking fish oil supplements, although rare, can include heartburn, nausea, or diarrhea. Patients taking fish oil and blood-thinning medications such as warfarin should be monitored by their doctors, as high doses of the fish oil can increase the risk of bleeding.

Write to Betsy McKay at

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