Men who consume large amounts of certain types of fish and supplements may have an increased risk of developing cancer of the prostate, a new study indicates.

The risks relate to omega-3 fatty acids, which are found in so-called oily fish, such as mackerel, herring and salmon, and are also taken by many people in the form of supplements.

Studies show that omega-3 has an important role to play in brain function and some research indicates it may reduce the risk of heart disease.

However, US scientists claim they have now confirmed that omega-3 can also increase a man's risk of developing prostate cancer. They say these findings confirm a similar link they found back in 2011 and also confirm the results of a large European study on this topic.

According to the scientists from the Fred Hutchinson Cancer Research Center, men with high concentrations of omega-3 fatty acids in their blood have a 71% increased risk of developing high-grade prostate cancer. High-grade tumours are more likely to be fatal, they warned.

Men with high levels of omega-3 also have a 44% increased risk of developing low-grade prostate cancer and a 43% increased risk of developing all types of prostate cancer.

"We've shown once again that use of nutritional supplements may be harmful. The consistency of these findings suggests that these fatty acids are involved in prostate tumorigenesis and recommendations to increase long-chain omega-3 fatty acid intake, in particular through supplementation, should consider its potential risks," the scientists said.

They also questioned the benefit of taking omega-3 supplements in an attempt to ward off heart disease. They pointed to an analysis recently published in the Journal of the American Medical Association, which looked at 20 studies, but found no reduction in heart-related events following supplementation.

The scientists insisted that what is important is that ‘we have been able to replicate our findings from 2011 and we have confirmed that marine omega-3 fatty acids play a role in prostate cancer occurrence'.

"It's important to note, however, that these results do not address the question of whether omega-3's play a detrimental role in prostate cancer prognosis," they pointed out.

They said that while it was unclear why exactly omega-3 increases the risk of prostate cancer, the fact that these findings had been replicated in two big studies shows that further research into the cause is required.

This latest study included over 800 men with prostate cancer and almost 1,400 men without the disease. Details of the findings are published in the Journal of the National Cancer Institute.

Every year in Ireland, over 2,000 men are newly diagnosed with cancer of the prostate, while 500 die as a result of the disease. For more information, click here