Fish Oil Supplements May Increase Risk of Stroke and Heart Disease for Some

Fish oil supplements might not be as good for your heart as we once thought, a new study suggests. At least, not for everyone.

Numerous studies have shown that eating fish is associated with a reduced risk of dying from heart disease or stroke. However, whether these same benefits can be achieved through taking fish oil supplements is less conclusive. Even so, roughly one in 13 American adults takes fish oil supplements on a semiregular basis, according to surveys from the National Center for Complementary and Integrative Health.

Historically, the side effects of fish oil supplements have been considered to be fairly mild, including bad breath, headaches and stomach issues. But, according to new research, regular fish oil supplementation might actually be increasing our risk of the very thing they are purported to prevent.

Fish oil supplements are often taken for their purported benefits on heart health. But the evidence supporting these assertions is somewhat unclear. magicmine/Getty

The study, published in the journal BMJ Medicine, drew on data from 415,737 participants from the U.K. between the ages of 40 and 69, nearly a third of whom regularly took fish oil supplements.

Over an average 12-year monitoring period, those with no known cardiovascular disease at the start of the study who regularly took fish oil supplements were 13 percent more likely to develop atrial fibrillation—a condition that causes an abnormal heart rhythm and increases your risk of stroke—and 5 percent more likely to have a stroke than those who did not take the supplements.

However, among those who had already developed cardiovascular disease before the study period, regular fish oil supplements were associated with a 15 percent lower risk of progressing from atrial fibrillation to a heart attack, and a 9 percent lower risk of progressing from heart failure to death.

On further analysis, women and nonsmokers with no heart health concerns at the start of the study who took regular fish oil supplements were at the highest risk of suffering heart attacks, strokes and heart failure by the end of the study period, while men and older participants were more likely to see protective effects.

This study was, of course, purely observational so no causal relationships can be concluded from its findings. Secondly, while the researchers did account for certain confounding variables—like smoking, sex, fish consumption and age—other confounding variables may still exist.

Thirdly, the researchers did not have access to information on the doses and formulations of fish oil supplements used by the participants. However, Deepak Bhatt, Director of Mount Sinai Fuster Heart Hospital and Professor of Cardiovascular Medicine at the Icahn School of Medicine at Mount Sinai, said that this research adds to a growing body of evidence that fish oil supplements may not be necessary, or indeed suitable, for the general population.

"Higher doses of prescription omega-3 fatty acid preparations have shown a slight increase in the risk for the heart arrythmia known as atrial fibrillation," Bhatt, who was not involved in the research, told Newsweek. "Thus, the high-quality studies that already exist do not support healthy people taking fish oil supplements, even though this is a very common and popular practice.

"The present observational study—which is a lower grade of evidence than randomized trials—also suggests that there is an increased risk of atrial fibrillation, so this is another word of caution in terms of using fish oil supplements. The present study did also suggest there might be a cardiovascular benefit, but given the limitations of this type of study design, for now it would be best to stick with what we know from the randomized trials— healthy people don't need to take fish oil supplements."

The study's authors add that further research is required to determine whether fish oil supplements have a causal effect on the development and prognosis of cardiovascular disease.

The full results can be found in the journal BMJ Medicine.

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