(The Hill) — Fish oil may increase the risk of stroke and heart conditions like atrial fibrillation, a new study found.

The study, published Tuesday in the journal BMJ Medicine, followed more than 400,000 people in the United Kingdom aged 40 to 69 for 12 years. Those people used fish oil supplements regularly.

Fish oil supplements are a source of omega-3 fatty acids and have been widely known to help with cardiovascular disease.

The research found that fish oil supplements may increase the risks for someone who does not already have a heart condition, but for those who already have cardiovascular issues, the supplement may reduce the risks.

The study found that regular use of fish oil supplements was associated with a 13% higher risk of developing atrial fibrillation and 5% heightened risk of having a stroke if the person had no known heart condition.

For patients with known heart disease, fish oil supplements were associated with a 15% lower risk of atrial fibrillation.

The authors noted that further studies are needed to determine the development and prognosis of heart disease events and how they work with fish oil supplements because the benefits and risks were not uniformly observed during the course of the study.