Taking large amounts of omega-3 fatty acids may be unwise for those with weakened immunity.
Researchers at the University of Missouri, Columbia, have been studying omega-3s for many years now and know that one of their effects is to damp down inflammation. That's why fish oils - rich in omega-3s - often benefit those with arthritis, a painful inflammatory condition of the joints. Yet the inflammatory response is a key component of the immune system in fighting infection.
The Missouri team studied how mice responded to bacterial infection when given diets containing either fish oil or no fish oil. Those on fish oil were slower to respond to the infection and more likely to die. This doesn't mean you should throw away your supplements, but be aware that very large doses may compromise your ability to fight infection - especially if you have reason to believe your immune system isn't as strong as it might be. The researchers are trying to better understand how omega-3s undermine the immune system - and may then be able to figure out ways of preventing this from happening.