High blood levels of omega-3 fatty acids from fish oil are associated with a slower rate of biological aging, researchers say. (Matt Rourke/Associated Press)

Diets rich in omega-3 fatty acids may help people with heart disease live longer by staving off the biological aging of cells.

Omega-3 fatty acids, found in salmon, tuna and other oily fish, were thought to help heart patients, but researchers knew little about why.

The latest findings, published in Tuesday's issue of the Journal of the American Medical Association, suggest that high levels of omega-3 in the blood are associated with a slower rate of biological aging.

Dr. Ramin Farzaneh-Far of the University of California at San Francisco and his colleagues focused on telomeres — strands of DNA at the end of chromosomes that resemble the plastic that holds the ends of shoelaces together.

"The main result from our study is that patients with high levels of omega-3 fish oil in the blood appear to have a slowing of the biological aging process over five years as measured by the change in telomere length," Farzaneh-Far said in a news release.

The length of telomeres shrink every time a cell divides, forming a chromosomal clock that reflects aging's toll.

Scientists suspect that as telomeres shrink, chromosomes become less stable and are therefore more likely to mutate. The 2009 Nobel Prize in Medicine was awarded for research into shortening telomeres.

608 patients followed

Farzaneh-Far's study looked at omega-3 fatty acid levels in the blood of 608 outpatients with stable coronary artery disease who were followed for an average of six years. The team also looked at telomere length in leukocytes, a type of blood cell.

"These findings raise the possibility that omega-3 fatty acids may protect against cellular aging in patients with coronary heart disease," the study's authors concluded.

It's possible that omega-3 fatty acids counteract the damage to cells that shortens telomeres, or that fish oil increases the production of an enzyme that lengths and repairs shortened telomeres, the researchers said.

The researchers said the findings underscore the American Heart Association's recommendation that people with heart disease get at least one gram a day of omega-3 fish oils in their diet.