Several American and Italian research institutes investigated the effects of fish oil supplementation on bleedings before, during, and after a surgical operation to prevent major bleedings. The study was conducted in 1516 patients who had a planned cardiac surgery. The study showed that fish oil supplementation did not increase the number of bleedings (which was assumed for a long time), and higher levels of fish oil were associated with a lower risk of bleedings. Additionally, a significantly lower need for blood units was required in the test group compared to the placebo group. More details can be found in the study.
Akintoye et al.