CHICAGO A diet rich in omega-3 fatty acids helps keep the DNA of heart patients from unraveling, which may help explain why fish oil is so beneficial after a heart attack, U.S. researchers said Tuesday.
"Cardiologists have known for a long time now that omega-3 fish oil seems to be beneficial for patients with coronary heart disease," said Dr. Ramin Farzaneh-Far of the University of California, San Francisco, whose study was published in the Journal of the American Medical Association.
"A number of studies over the last 20 years or so have shown that after patients have had a heart attack, taking fish oil through diet or supplements is able to reduce the risk of a subsequent heart attack or death from coronary heart disease," Farzaneh-Far said in a telephone interview.
What has not been clear is why fish oil is so beneficial.
"In this study, we decided to look at a new mechanism by which omega-3 fatty acids might work," Farzaneh-Far said.
The team focused on telomere length -- the length of protective caps on the ends of chromosomes that carry DNA.
Fraying or shortening of these protective caps can lead to premature aging and cancer, a new understanding of aging that helped Elizabeth Blackburn and the two other Americans win the 2009 Nobel Prize in Medicine.
Farzaneh-Far and colleagues measured the length of telomeres in blood cells in 608 heart attack patients to see if there was any association between the levels of omega-3 fatty acids and the change in telomere length over time.
"We found a very clear association that increasing levels of the amount of omega-3 fish oil in the blood was associated with a decrease in the rate of biological aging," Farzaneh-Far said.
Those with the highest levels of omega-3 fatty acids had the longest telomeres, while patients with low levels of the compounds had shorter telomeres, he said.
None of the patients were given supplements and the team did not collect dietary information, so it is not clear just how much fish oil it took to have an effect. While fish oil is a primary source of omega-3 fatty acids, they are also found in walnuts, flaxseed oil and leafy green vegetables.
The findings offer a biological explanation for why fish oil helps heart patients.
It may be that omega-3 fatty acids counteract oxidative stress -- a cell-damaging chemical reaction that can shorten telomeres, Farzaneh-Far said.
Or it may be that fish oil increases the production of telomerase -- an enzyme that lengthens and repairs shortened telomeres.
"Both of those mechanisms have to be proven," he said.
Farzaneh-Far said the team only studied the effects of fish oil and cellular aging in heart patients, so it is not clear if the association would hold true in healthy people.
"There is no reason to think that it wouldn't. But we haven't shown that," he said.
(Editing by Cynthia Osterman)