Fish oil has been considered heart healthy for decades, and many people choose to take over-the-counter supplements to reduce their risk of heart disease. Still, research has produced conflicting results as to whether there are any real health benefits.
Most studies have shown that the cardiac benefits associated with fish oil supplements are minor and the potential risks involved may not be worth it. However, new evidence suggests that high doses of prescription fish oil can actually damage the heart.
A clinical trial led by the Cleveland Clinic was terminated prematurely because prescription doses not only failed to reduce severe cardiac events, but also appeared to increase the risk of atrial fibrillation, an irregular heartbeat that can lead to blood clots, stroke, or heart failure.
The study, known as the STRENGTH study, included 13,078 patients who received either daily high-dose omega-3 fatty acids or corn oil placebos.
The results contrast sharply with the more promising results of a 2018 study that found that a highly pure form of fish oil had cardiovascular benefits when compared to a mineral oil placebo.
However, many cardiovascular health experts consider the earlier study to be controversial. The mineral oil negatively affected cholesterol and inflammation markers, which may have exaggerated the benefits of the fish oil supplement.
“Compared to mineral oil used in the previous study, corn oil did not increase levels of bad cholesterol or markers of inflammation, which suggests it is a really neutral placebo,” says senior author Dr. Steven Nissen, chief academic officer of the Heart, Vascular and Thoracic Institute at the Cleveland Clinic, said in a statement.
The STRENGTH study was conducted in 675 hospitals worldwide. Researchers attempted to monitor the effects of fish oil supplements on cardiovascular death, non-fatal myocardial infarction, non-fatal stroke, coronary artery revascularization, and hospitalization for unstable angina.
The study was discontinued after a primary endpoint was met in 1,384 patients. At the end of the study, 785 patients in the intervention group and 795 in the placebo group had a major cardiovascular event.
The study showed a 67% increase in atrial fibrillation in the participants who received the fish oil supplements.
“Given that two large clinical studies have now shown a higher incidence rate of atrial fibrillation with high-dose omega-3 fatty acids, this observation needs further investigation.” said Dr. Michael Lincoff, vice chairman of the cardiovascular medicine department at the Cleveland Clinic.
The study results also suggest that a review of all fish oil products should be considered, including over-the-counter diet supplements, he added. They follow a UK study published last spring that found that fish oil supplements slightly increased the risk of prostate cancer.
Health experts emphasize that it is It is important to weigh all of the potential benefits and risks when considering dietary supplements. They advise people to consult their doctor before adding or stopping any dietary supplement.