A new large, long-term study published in the British Medical Journal today suggests that taking regular fish oil supplements may increase the risk of developing heart disease and stroke in healthy people. However, the study showed that regular fish oil supplementation benefited people with existing cardiovascular disease (CVD), by slowing disease progression and reducing risk of death. 

The study tracked the progress of over 400,000 participants enrolled in the UK Biobank study over an average period of 12 years, collecting data on health status and fish oil use (classifying participants and regular or non-users). 

The study showed that in people with a healthy cardiovascular profile, regular use of fish oil supplements was associated with a 13% heightened risk for developing atrial fibrillation and a 5% heightened risk of having a stroke. 

But for participants with existing heart disease, regular use of fish oil supplements was associated with a 15% lower risk of progressing from atrial fibrillation to a heart attack, and a 9% lower risk of progressing from heart failure to death. 

The researchers say their study shows that regular use of fish oil supplements might have different roles in the progression of cardiovascular disease. They conclude that further studies are needed to determine the precise mechanisms for the development and prognosis of cardiovascular disease events with regular use of fish oil supplements.

The researchers note that this is an observational study and that no causal relations can be drawn from the findings. 

Tracy Parker, a senior dietitian at the British Heart Founn dation, told The Guardian: “In the UK, Nice guidelines don’t recommend taking fish oil supplements to either prevent heart and circulatory diseases or stop another heart attack. Supplements such as omega-3 fatty acids are no substitute for a healthy diet and, instead of focusing on individual nutrients, it’s important to look at your diet as a whole to help lower your risk.”