MONDAY, March 7 (HealthDay News) -- For years, nutritionists have known that eating oily fish like mackerel or salmon boosts human health, although the exact reasons have remained unclear.

A new study may have solved that riddle.

Researchers say they've identified a powerful anti-inflammatory blood fat in humans that's derived from omega-3 fatty acids sourced from fish oil.

The lipid, called resolvin E1, was detected in plasma taken from study volunteers who were given omega-3 fatty acids and aspirin, both of which are used to lower inflammation.

Reporting in the March 7 issue of the Journal of Experimental Medicine, the researchers believe resolvin E1 inhibits the migration of inflammatory cells to sites of inflammation, and also curtails the activity of other inflammatory cells.

This finding may help explain how a diet high in oily fish helps reduce inflammation, particularly when used along with low doses of aspirin, according to the investigators.

The information in this study also suggests potential problems with cox-2 inhibitor drugs (which include Vioxx and Celebrex) that are meant to block inflammation. These drugs have been shown to have negative cardiovascular side effects.

The study authors noted that cox-2 plays a role in making resolvin E1. They suggest that inhibition of vascular cox-2 by cox-2 inhibitor drugs may block production of resolvin E1, thus eliminating an important natural anti-inflammatory response. They stress, however, that no research has yet been conducted to confirm this theory.

More information

The Cleveland Clinic Foundation has more about inflammation.