New large-scale research has found that despite their previous recorded benefits for cardiovascular disease, fish oil supplements do not appear to prevent heart attacks or strokes in patients with diabetes.

Led by Nuffield Department of Population Health, University of Oxford, UK, the ASCEND trial (A Study of Cardiovascular Events iN Diabetes) looked at 15,480 patients over the age of 40 with diabetes but no history of cardiovascular disease.

Participants were randomly split into two groups, with one given 1 gram of fish oil supplements daily and the other a matching placebo capsule of olive oil, and followed for an average of 7.4 years.

During this time 689 (8.9 percent) of the participants taking fish oil supplements and 712 (9.2 percent) of those taking a placebo experienced their first serious vascular event, which included non-fatal heart attacks, non-fatal strokes, "mini-strokes," or deaths from a cardiovascular cause, with the researchers commenting that there was no statistically significant difference between the two groups.

The rates of deaths from any cause were also similar in the fatty acid group and the placebo group.

Although previous observational studies have found that a higher consumption of fish is associated with lower risks of coronary artery disease and stroke, these studies can be prone to bias, and the finding had not been confirmed in randomized trials.

It was also unclear what effect fish oil had on lowering the risk in those with diabetes, a population which has a two to three times increased risk of cardiovascular disease compared to the general population, according to previous research.

Principal investigator Dr. Louise Bowman commented on the findings saying, "Our large, long-term randomized trial shows that fish oil supplements do not reduce the risk of cardiovascular events in patients with diabetes."

"This is a disappointing finding, but it is in line with previous randomized trials in other types of patients at increased risk of cardiovascular events which also showed no benefit of fish oil supplements. There is no justification for recommending fish oil supplements to protect against cardiovascular events."

The findings were presented at the European Society of Cardiology (ESC) Congress happening this week in Munich, Germany, and published in the New England Journal of Medicine.