Can Regular Use of Fish Oil Supplements Harm Heart Health?

Fish oil is once again in the news because of a recently published study in BMJ Medicine. According to various headlines, taking fish oil supplements increases the risk of stroke and heart disease in healthy individuals. However, there is much more to the story.

This was a large observational study featuring 415,737 participants who identified their use of fish oil supplements via a self-reporting touchscreen questionnaire during the baseline survey. Responses were not verified at the end of the study, so it is unknown as to the consistency of the fish oil consumption throughout the study, which lasted four years with a median follow-up of 11.9 years.

The study showed that for healthy people, regular use of fish oil supplements was associated with an increased risk of atrial fibrillation (Afib) and stroke. Conversely, for participants diagnosed with Afib, regular fish oil use had a protective effect by helping to reduce the risk of myocardial infarction, heart failure, and death.

“The magnitude of risk of Afib among the participants who took the fish oil was small—13 percent, which is hardly enough to warrant the conclusion that regular use of fish oil supplements increases the risk of Afib and stroke,” explained respected integrative medical expert Ronald Hoffman, MD. “The risk of stroke was very slight and did not distinguish between thrombotic versus hemorrhagic strokes. While it’s plausible that fish oil’s blood-thinning effects might lead to more hemorrhagic strokes, it’s also possible that those strokes were a consequence of new-onset Afib in non-anti-coagulated individuals.”

As an observational study, the authors point out, “…no causal relations can be drawn from our findings.” Some covariate information such as smoking and alcohol intake were collected, however, the authors state that “residual confounding could still exist.”

“As with much nutritional epidemiology, it’s hard to tease out the impacts of uncontrolled variables on the outcomes,” said Dr. Hoffman, who is host of the Intelligent Medicine radio show and podcast. “For example, it’s possible that the participants in the fish oil group were taking it because of health issues. Also, the cohort of fish oil users were older and predominantly white females, which are potential confounders.”

In addition, the study questionnaire and interview administered at the beginning of the study only asked a yes/no question about fish oil intake and did not identify the type, quality, or dosage of the fish oil supplements, which can all influence outcomes.

The Clinical Bottom Line

Research is indeed conflicting in this area. For example, a 2021 systematic review and meta-analysis found that eating more fish and long-chain omega-3 fatty acids had a protective effect by lowering the risk of stroke, in particular ischemic stroke. Whereas an older 2012 systematic review and meta-analysis showed no significant association between omega-3 supplementation and lower risk of all-cause mortality, cardiac death, sudden death, myocardial infarction, or stroke.

And yet, in 2018 the American Heart Association published their scientific statement concluding that one to two seafood meals per week should be recommended to reduce the risk of congestive heart failure, coronary heart disease, ischemic stroke, and sudden cardiac death. Fish oil supplements are often prescribed because many patients do not eat that amount of fish weekly.

For Dr. Hoffman, who typically recommends fish oil to his patients, this latest study will not influence his prescribing.

“For patients at high risk of stroke, it seems counterintuitive to recommend administering prescription blood thinners for prevention while withholding fish oil that also confers anti-thrombotic benefits,” said Dr. Hoffman. “For patients with Afib, this study demonstrated that fish oil supplementation provided a modest degree of protection from death, so those patients should certainly take a fish oil supplement.”

Another aspect to consider is that omega-3 fatty acids have been shown to benefit several key body systems in addition to the heart including the brain, joints, reproductive system, immune system, and others.

"I'm encouraged by this study's findings, which substantiate omega-3s benefits in people with known cardiovascular disease or those who have high-risk factors, which comprises a sizeable percentage of the adult American population," concluded Dr. Hoffman. "For the average healthy person, the harm in taking fish oil supplements is minimal or non-existent, and the benefits are many."