Scientists know that omega-three fatty acids in fish oil can help people with heart disease live longer. Cold water fish like salmon and tuna contain omega-three fatty acids. These fatty acids are mainly found in fish oil. They are also in some vegetable oils and foods like walnuts. Earlier studies showed that omega-three fatty acids can decrease the risk of coronary artery disease. But until now, no one knew why they are so helpful.

Coronary artery disease is a leading cause of death throughout the world. The disease results when plaque builds up inside coronary arteries and blocks the flow of blood to the heart.

Ramin Farzaneh-Far is an assistant professor of medicine at the University of California in San Francisco. He led a study to see if there might be a link between omega-three acids and the aging of cells. To do this, his team examined telomeres -- the protective covers on the ends of chromosomes. Scientists believe that the shortening of telomeres over time leads to cell death.

His research team measured the length of telomeres in blood cells from six hundred heart disease patients. The patients all had taken part in the Heart and Soul Study, which lasted from two thousand to two thousand two. Blood from the patients was tested for omega-three fatty acids.

Doctor Farzaneh-Far says his team wanted to see if there was any link between the fatty acid levels and the change in telomere length over time.

"Patients with the highest levels of omega-three fish oils were found to display the slowest decrease in telomere length, whereas those with the lowest levels of omega-three fish oils in the blood had the fastest rate of telomere shortening, suggesting that these patients were aging faster than those with the higher fish oil levels in their blood."

The Journal of the American Medical Association published the results of the study. The team did not study how much fish oil the patients were receiving, so the amount needed to have an effect is unclear.

Doctor Farzaneh-Far says the results confirm what the American Heart Association advises for patients with coronary artery disease. That is to eat fish two times a week, or have at least one gram a day of omega-three fish oil. Fish oil is not the only thing that can affect telomere length. But the researchers say it does have an influence. The researchers did not study the effect of omega-three fatty acids in people without heart disease. But they note that telomere shortening happens in everyone.