The health benefits of fish oil are not universal, and taking it may even increase the risk of certain types of cardiovascular disease (CVD) in some people.

During an interview on NTDTV’s “Health 1+1,” Dr. Liu Zhongping, a Taiwanese cardiologist, discussed fish oil’s efficacy, risks, and contradictions based on the latest research reports. He also provided recommendations on how to ensure safe fish oil intake.

Fish oil is a popular dietary supplement because it is rich in polyunsaturated omega-3 fatty acids. Its main compounds, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are widely recognized for their benefits to cardiovascular health.

However, ongoing debate surrounds the dosage, EPA and DHA concentrations, and potential contamination with heavy metals.

Risks Associated With Fish Oil

Recent studies reveal nuanced insights into the risks associated with fish oil supplements.

A prospective cohort study published in May 2024 in BMJ Medicine found that people without prior CVD who consumed fish oil regularly had an increased risk of atrial fibrillation and stroke—increases of 13 percent and 5 percent, respectively.

In contrast, CVD patients who regularly took fish oil experienced reduced risks of both conditions. The risk of death from heart failure due to fibrillation converting to major adverse cardiovascular events, or atrial fibrillation converting to heart attack, was also reduced as a result.

The study followed data from nearly 416,000 people aged 40 to 69 from the UK Biodata Database. The average follow-up was about 12 years.

Additional studies offer mixed results regarding the effects of omega-3 fatty acids on cardiovascular health.

A 2021 systematic review and meta-analysis of seven large randomized controlled trials confirmed the association between medium- and long-term supplementation with marine omega-3 fatty acids and increased risk of atrial fibrillation, particularly at dosages exceeding 1 gram per day.

However, another meta-analysis of 29 prospective studies published in December 2023 shows that the levels of EPA, DHA, and EPA plus DHA in the body were inversely related to the risk of total stroke and ischemic stroke but had no association with hemorrhagic stroke. The study concluded that higher dietary intake of DHA and EPA was expected to reduce stroke risk.

A large-scale, nationwide randomized trial sponsored by the National Institutes of Health (NIH) did not find that marine omega-3 fatty acids increased or reduced the risk of atrial fibrillation or affected the risk of stroke. The trial, called VITAL, followed 25,871 adults aged 50 and older across the United States for more than five years.

A 2023 meta-analysis of studies published by the VITAL research team shows that supplementation with marine omega-3 fatty acids at 1 gram per day, compared with olive oil placebo, did not significantly reduce the risk of heart attack, stroke, heart disease, and mortality from vascular disease. However, it did significantly reduce the risk of total heart attack, percutaneous coronary intervention (a procedure used to treat narrowed or blocked coronary arteries), fatal heart attack, and recurrent hospitalization for heart failure.

Who Should Take Fish Oil Supplements?

EPA and DHA, the omega-3 fatty acids in fish oil, are essential for maintaining healthy bodily functions. Their health benefits include improving certain obesity-related metabolic syndromes such as insulin resistance, hypertension, and dyslipidemia by lowering plasma triglycerides. Their blood pressure-lowering and anti-inflammatory properties, resulting in better vascular function, may bring added cardioprotective effects.

“We think that omega-3s have coronary or heart benefits and some people seem to benefit more than others,” Dr. JoAnn E. Manson, principal investigator of the VITAL trial and chief of the division of preventive medicine at Brigham and Women’s Hospital and Harvard Medical School, said in an NIH research feature article.

Some groups that may benefit from fish oil supplements are African Americans and people with low fish intake and two or more risk factors for heart disease.

Liu emphasized that healthy people, especially those consuming fish twice weekly, may not need additional fish oil. Conversely, CVD patients could benefit from supplementation.

A 2021 meta-analysis found that supplementation with EPA and DHA is a practical lifestyle strategy for CVD prevention, particularly for coronary heart disease and heart attack, and the protective effect appears to increase with dosage.

People Who Shouldn’t Supplement Fish Oil

Fish oil is not suitable for everyone, including the following people, according to Liu:

• Those allergic to fish.
• Those prone to bleeding. Fish oil has an anticoagulant effect and is not suitable for women with bleeding hemorrhoids or intense menstruation, nor is it suitable for pregnant women or patients preparing for surgery.
• Those who take aspirin. Many people take aspirin to maintain or prevent CVD. Studies have shown that aspirin and fish oil may interact with one another, so be cautious when using them concurrently.

Liu said aspirin is essential for managing heart disease, and one should never stop taking it to supplement fish oil. If you are taking aspirin but would like to take fish oil, consult your doctor first.

Omega-3s From Natural Foods

Obtaining omega-3 fatty acids from natural foods may be safer and more effective than relying on supplements. Liu recommends the following natural foods:

• Fish and Seafood: Salmon, mackerel, and sardines are all rich in DHA and EPA.
• Plant-Based Oils: Flaxseed and walnut oils contain alpha-linolenic acid (ALA), an essential fatty acid that can be converted into EPA and DHA in the body. Although less efficient than EPA and DHA, it is still a good plant-based option.
• Nuts and Seeds: Walnuts, flaxseeds, and chia seeds are all rich in omega-3 fatty acids.

Safe Supplementation With Fish Oil

For people considering fish oil supplementation, Liu recommends adhering to the following guidelines to minimize risks:

• Control the Dosage: Limit the daily intake of fish oil to less than 1 gram to prevent potential risks such as atrial fibrillation.
• Choose Natural Foods: Prioritize getting omega-3 fatty acids from fish and other natural foods to avoid overreliance on supplements.
• Watch Out for Contaminants: Choose fish with low mercury levels, such as salmon and sardines, and avoid those with high mercury levels, such as swordfish and king mackerel.
• Consult Physicians: Use fish oil supplements under the guidance of a doctor, especially if you have CVD or other health conditions.