(Health.com) -- Fish oil supplements, widely touted for their ability to improve heart health, may not be as useful in protecting the heart as once thought, according to a new study in the Journal of the American Medical Association.
Fish oil supplements contain omega-3 fatty acids, which are found in salmon and other cold-water fish.
These healthy fats have been shown to lower blood pressure, reduce triglycerides, and prevent heart rhythm abnormalities, but clinical trials investigating whether these properties translate into a lower risk of heart attack and stroke have had mixed results.
In the new study, researchers sought to resolve these inconsistent findings by re-examining data from 20 previous clinical trials involving nearly 70,000 patients.
Overall, they concluded, fish oil supplements were no more effective than a placebo at preventing premature death or serious cardiovascular problems.
"Omega-3 supplementation did not statistically significantly reduce all-cause mortality, sudden and cardiac death (heart attack), or stroke," says Dr. Moses Elisaf, the senior author of the study and a professor of internal medicine at the University of Ioannina Medical School, in Greece.
The study isn't the first to cast doubt on the benefits of fish oil. In April, a similar analysis of previous research found that the supplements did not help prevent second heart attacks or strokes in people with cardiovascular disease.
Diets rich in fish and omega-3s have been linked to a lower risk of heart attack, so what accounts for the disappointing results from supplement trials?
Inconsistencies in the trial details -- such as the dosage used and the participants' preexisting conditions -- may be partly responsible, but it could also be that fish oil doesn't provide the same benefits as omega-3s in their natural state.
In theory, the omega-3s found on drugstore shelves are no different than those found in fish and other dietary sources, such as flaxseed. In reality, however, the concentrated dose provided by supplements may behave differently in the body than the slow and steady intake that comes with food.
That pattern has been observed with other types of supplements, says Dr. John Erwin III, a cardiologist at the Texas A&M Health Science Center College of Medicine, in Temple, Texas.
For instance, diets that are naturally high in vitamins C and E appear to reduce the risk for heart disease, but the corresponding supplements don't, and may even harm the heart, Erwin says.
Similarly, studies have suggested that calcium supplements -- but not a calcium-rich diet -- may actually contribute to heart attacks in postmenopausal women.
It's too soon to say why fish oil supplements haven't proven more effective. Questions regarding dosage and other variables will need to be explored further before doctors can confidently recommend fish oil supplements (or not) to their heart patients, Elisaf and his colleagues say.
In the meantime, people looking to boost their heart health should continue to eat plenty of fish. Erwin urges his patients to eat two to three servings of cold-water fish weekly. Anchovies, sardines, mackerel, herring, lake trout, and albacore tuna are all good sources of omega-3s, as is salmon.
"Most of us who are doing prevention for heart disease still feel strongly that a diet that's based on higher amounts of cold-water fish consumption is a healthy thing," he says.
Copyright Health Magazine 2011