Fish oil is a popular supplement in the United States. It’s been reported that 20% of US adults over the age of 60 take fish oil supplements for their purported health benefits.

Assadourian JN, Peterson ED, McDonald SA, et al. Health Claims and Doses of Fish Oil Supplements in the US. JAMA Cardiology. 2023;8(10):984-988.

Thousands of fish oil supplements are on the market, and the majority claim to provide positive health effects. However, in many cases, the Food and Drug Administration (FDA) doesn't approve label claims on fish oil supplements. Now, new research published in BMJ Medicine suggests that regular fish oil supplement use may be linked to an increased risk of heart disease.

Chen G, Zhengmin MQ, Zhang J, et al. Regular use of fish oil supplements and course of cardiovascular diseases: prospective cohort study. BMJ Medicine. 2024;3(1).

 

United Kingdom-based researchers looked at data from 415,737 participants. The mean participant age was 55.9, and 55% of patients were women. Researchers excluded participants with a history of heart failure, stroke, cancer, atrial fibrillation, or myocardial infarction. Participants were asked whether they regularly used fish oil supplements at the onset of the study. About 31.4% of participants reported regularly using fish supplements.

Participants were followed until the trial's end date, death, or data could no longer be collected, with a median follow-up time of 11.9 years. Researchers collected data that allowed them to take factors such as diet, demographics, lifestyle, prescribed medications, and comorbidities into account. 

Fish oil use was found to be more common among older participants. Additionally, use was more common among participants who identified as white and female. Fish oil supplement users were also more likely to consume higher amounts of alcohol and fish than nonusers. 

Over the course of the study, 18,367 participants developed atrial fibrillation (AFib), and regular use of fish oil supplements was linked to an increased risk of development. Fish oil supplement use was also linked to a slightly increased risk of stroke.

However, 17,826 study participants experienced major adverse cardiovascular events, and fish oil use was not found to have increased the risk of these events. Additionally, among participants who developed AFib, 4,810 developed major adverse cardiovascular events and 1,653 died. Fish oil users who developed AFib were found to have a reduced risk of major adverse cardiovascular events and death. 

Fish oil supplement users also had a lowered risk of heart failure. Fish oil users in the study who developed heart failure were found to have a lower risk of death. Similarly, participants who developed AFib and used fish oil were found to be at a lower risk of myocardial infarction than nonusers. 

Fish oil’s link to increased risk of major adverse cardiovascular events was found to be stronger in women and non-smokers. The supplements’ protective effects were observed to be strongest in men and older participants. 

Overall, the findings suggest that fish oil supplements could be linked to an increased risk of AFib, but that they could have a protective effect for people with a pre-existing heart health condition. Discussing this, the study’s authors concluded: “Further studies are needed to determine whether potential confounders modify the effects of oil fish supplements and the precise mechanisms for the development and prognosis of cardiovascular disease events.”

 

Supplements and safety

 

As is the case for many supplements, the research on fish oil supplements is unclear. For instance, although a strong link between a diet that includes seafood and a lowered risk of heart disease has been established, that same link between supplements that contain omega-3 fatty acids, such as fish oil, has not been proven.

NCCIH. Omega-3 Supplements: In Depth. 2018.

There is also inconclusive evidence linking fish oil to some of its other often-claimed benefits, such as slowing the progression of eye disease. However, there is a link between high doses of omega-3 fatty acids and reduced triglyceride levels.

 

Other supplements are often similar; while they typically have some scientifically proven benefits, it’s common for them to claim a variety of benefits that are not proven or backed by the FDA. It’s also common for patients to not disclose supplement use to their physicians, leaving them unable to prevent drug interactions and other potential safety hazards.

Guzman JR, Paterniti DA, Liu Y, et al. Factors Related to Disclosure and Nondisclosure of Dietary Supplements in Primary Care, Integrative Medicine, and Naturopathic Medicine. Journal of Family Medicine and Disease Prevention. 2019;5(4).

 

The American Medical Association (AMA) recommends asking all patients about supplement use and having an open discussion with them about their responses. Writing in the AMA Journal of Ethics, Valerie Clinard, PharmD, APh, and Jennifer D. Smith, PharmD, BCACP, BC-ADM, CDCES advise:

“Overall, when a patient is using or has intentions to use a dietary supplement in place of a prescribed agent, practitioners should approach this decision from the standpoint of the safety and efficacy of the agent. If the product appears safe and has some data supporting its efficacy for the intended use, practitioners should support the patient’s decision to trial the agent for a specified time period. If the agent’s safety or efficacy is unknown, practitioners should discuss these concerns with the patient and consider if there might be an appropriate dietary supplement alternative for the intended purpose.”

Clinard V, Smith JD. How Should Clinicians Respond to Patient Interest in Dietary Supplements to Treat Serious Chronic Illness? AMA Journal of Ethics. 2022;24(5):361-367.