The fish oils may allow health professionals to use new treatments against stroke and sepsis

A new discovery about the health benefits of fish oil could pave the way to new treatments for life-threatening conditions such as sepsis and stroke, say scientists.

Researchers found that the body converts a fatty acid in fish oils into a powerful anti-inflammatory biochemical called resolvin D2.

It was this chemical that accounted for the ability of fish oil to combat diseases such as rheumatoid arthritis.

The British and American scientists believe resolvin D2 could provide the basis of new treatments for a range of serious diseases which involve inflammation. The list includes sepsis - a potentially deadly reaction to infection which causes inflammation to rage through the body - stroke, and arthritis.

Laboratory experiments showed how the body converts the fish oil fatty acid DHA into resolvin D2, and revealed the chemical's structure.

Professor Mauro Perretti, from Queen Mary, University of London, who led the UK team, said: "We have known for some time that fish oils can help with conditions like arthritis which are linked to inflammation. What we've shown here is how the body processes a particular ingredient of fish oils into resolvin D2.

"We've also looked in detail at this chemical, determining at least some of the ways it relieves inflammation. It seems to be a very powerful chemical and a small amount can have a large effect.

"This research is important because it explains at least one way in which fish oils can help in different types of arthritis. We can also work on this chemical and see if it can be used not only to treat or even prevent arthritis, but also as a possible treatment for a variety of other diseases associated with inflammation."

Inflammation, caused when the immune system goes into "overdrive", is known to play a role in many health problems ranging from heart disease and stroke to arthritis and cancer.

Previous research has shown that a key step in the inflammatory process occurs when white blood cells stick to the inner lining of blood vessels.