NEW YORK - Fish oil supplements did not prevent heart problems in people who hadn't had a heart attack yet, in a large long-term study from Italy.
The study - a gold-standard randomized, controlled trial - tested the effect of omega-3 fatty acids, which are found in oily fish such as tuna or sardines. Patients in the study had risk factors for heart disease, such as high blood pressure, high cholesterol, a history of smoking or narrowed arteries. But patients who had a heart attack in the past weren't allowed to enroll.
Five years after the study began, 11.7 per cent of the 6,244 patients taking a capsule containing one gram of fish oil daily had died or been hospitalized for heart problems, compared to 11.9 per cent for the 6,269 volunteers who instead received one gram of olive oil every day as a placebo.
The result, reported in the New England Journal of Medicine on Wednesday, is in sharp contrast to other research suggesting that omega-3 fatty acids can help those who have survived a heart attack or suffer from heart failure.
For people who haven't had a heart attack, though, the new findings "provide no evidence of the usefulness of (omega)-3 fatty acids for preventing cardiovascular death or disease," according to the research team, led by Dr. Maria Carla Roncaglioni of the Mario Negri Institute for Pharmacological Research in Milan.
She told Reuters Health in an email that the finding argues against the use of fish oil supplements, at least among Italians, who are already exposed to the Mediterranean diet. "There is no reason to prescribe fish oil supplementation unless they have a heart attack," she said.
The researchers did see a reduction in hospital admissions for heart failure and a preventive effect in women, but "both may be due to chance, although they are consistent with two findings from other studies," the researchers said.
Alice Lichtenstein, from Tufts University in Boston and a spokeswoman for the American Heart Association, told Reuters Health the findings from the new study are further evidence that, in general, "just giving a supplement on top of a non-heart-healthy lifestyle doesn't seem to help."
"We thought vitamin E pills were going to be the answer and that turned out to be wrong. We though beta carotene as an antioxidant was going to reduce cardiovascular disease . . . and that pill didn't work," she said in a telephone interview. "It's the whole package, not just popping one pill."
The patients in the Italian study were treated by 860 general practitioners throughout the country. Their average age when they enrolled in the study was 64 years old.
Originally, the researchers had thought the main goal of their study would be to see how many people died or had a heart attack or stroke. But those events turned out to be less common than expected, probably because the patients "were rather intensively exposed to recommended preventive treatment (including healthy lifestyle habits) by their family physicians," Roncaglioni said.
Thus, the goal of the study was modified to count anyone who died or was admitted to the hospital for a heart-related cause.
Certain factors did seem to improve slightly more in the fish oil recipients, such as levels of fat and "good" cholesterol in the blood.
But other measures such as "bad" cholesterol, blood pressure and blood sugar remained similar in the fish oil and olive oil groups, and there was no difference in the proportion of patients in the two groups who needed heart medications.
Roughly two of every 100 patients died of heart disease, regardless of which group they were in. And roughly 10 of every 100 patients in each group needed to be hospitalized for a heart-related problem.
By the end of the study, 18 per cent had stopped taking their fish oil and 19 per cent had stopped taking their olive oil. When those volunteers were excluded from the study, there was still no significant difference between the groups in the risk of death or hospitalization for heart problems.
The rates of gastrointestinal side effects, cancer and bleeding were comparable in the two groups.
The US Food and Drug Administration says olive oil has heart benefits of its own. Is it possible that using olive oil as the placebo in this study skewed the results by protecting the placebo group to some extent? Roncaglioni doesn't think so.
She said giving olive oil as a placebo probably did not bring down the overall rate of heart problems in that group because "one gram of olive oil corresponds to only 1/30th of the mean amount consumed in the Mediterranean diet," which would make it of very small benefit.