Supporting recommendations that people eat a couple of servings of fish per week, a new study suggests adults with the highest levels of omega-3 fatty acids in their blood are less likely to die from a range of causes including cancer than those with the lowest levels.
Out of about 2 700 older Americans, researchers found people with the most circulating omega-3s – usually found in oily fish such as tuna or sardines – lived about two years longer than those with the lowest levels, on average.
Dr Dariush Mozaffarian, the study's lead author from Brigham and Women's Hospital and Harvard Medical School in Boston, said the findings suggest people should work more oily fish into their diets.
"The vast majority of Americans don't eat two servings of fish per week. That would be ideal," Mozaffarian said.
Omega-3 fatty acids have long been thought to offer protection against a lengthy list of health problems – from premature births to heart disease. But study results have been mixed. Some relied on participants remembering how much oily fish they ate; others tested the effects of supplements on top of people's usual diets.
For the new study, researchers took blood samples from 2 692 US adults over age 65 in 1992 and 1993. The participants did not have heart disease at the beginning of the study.
Researchers measured the amount of omega-3 fatty acids in participants' blood, and then tracked them until 2008 to see how many died from various causes. Overall, 1 625 of the participants had died by the end of the study, the researchers reported Monday in the Annals of Internal Medicine.
Mozaffarian and his colleagues found people who had the highest levels of omega-3 fatty acids in their blood at the outset were 27% less likely to die for any reason over the course of the study, compared to those with the lowest levels.
That worked out to be about two extra years of life after age 65 for people at the high end of the omega-3 fatty acid spectrum.
Most of that benefit, according to the researchers, came from a halving of the rate of heart disease deaths among people with high fatty acid levels.
The new study doesn't prove omega-3 fatty acids were responsible for keeping people alive, according to Alice Lichtenstein, the director of Tufts University's Cardiovascular Nutrition Laboratory in Boston.
"Those people who consume more fish also consumed a higher level of fruit, more vegetables and less red meat. The question is, is it just that they consumed more fish, or is it a dietary pattern?" said Lichtenstein, who was not involved with the new research.
She said the people least likely to die during the study seemed to have diets that mirrored recommendations from the US Department of Agriculture and the American Heart Association.
"I think people should avoid thinking any single food or supplement is going to be a substitute for a generally healthy lifestyle. Whether it's this paper or any that comes out in the future, we need to face the fact that it's the whole package and not just one individual component," Lichtenstein said.