Big studies give long-awaited answers on who does and does not benefit from these popular nutrients. Fish oil taken by healthy people, at a dose found in many supplements, showed no clear ability to lower heart or cancer risks. Same for vitamin D.

But higher Amounts of a purified, prescription fish oil slashed heart problems and heart-related deaths among people with high triglycerides, a type of fat in the blood, and other Risks for heart disease. 

Doctors cheered the results and said they could suggest a new treatment option for hundreds of thousands of patients like these. Up to 10% of US adults take fish oil. Even more take vitamin D, despite no major studies to support the many health claims made for it.

"Those who peddle it promote it as good for everything," but in this definitive test, vitamin D "showed a big nothing," said Dr. James Stein, a heart specialist at the University of Wisconsin-Madison. He had no role in the studies or ties to the companies involved. Results were revealed Saturday at an American Heart Association conference in Chicago and published by the  New England Journal of Medicine.

About fish oil

These oils, also called omega-3 fatty acids, are found in salmon, tuna and certain other fish. They reduce triglycerides and inflammation and may have other effects There are different types, including EPA and DHA.

One study tested 4 grams a day of Amarin Corp.'s prescription Vascepa, which is concentrated EPA, in more than 8,000 patients with high triglycerides and a greater risk of heart problems for various reasons. All were already taking a statin such as Lipitor or Zocor to lower cholesterol. Half were given Vascepa and the rest, mineral oil capsules as a comparison.

After five years, about 17% of those on Vascepa had one of these problems-a heart attack, stroke, heart-related death or clogged arteries requiring medical care-versus 22% of the others. That worked out to a 25% reduction in risk

"Looked heart attacks, heart attacks, heart attacks, and strokes all were lower with Vascepa. Only 21 people would need to take Vascepa for five years to prevent one of the main problems studied-favorable odds," Stein said.

Side effects may be a concern: More people on Vascepa were hospitalized for an irregular heartbeat-3% versus 2% of the comparison group. Doctors say that's puzzling because other research suggests fish oil lowers that risk.

A broader test

The other study tested to lower 1 gram daily dose of a different type of oil-an EPA / DHA combo sold as Lovaza or Omacor and in generic form-in 26,000 people with no prior heart problems or cancer.

After about five years, rates of a combined measure of heart attacks, strokes, and other problems were similar for fish oil users and a comparison group. Cancer rates and deaths were also similar.

There were fewer heart attacks in the fish oil group-145 versus 200 in the comparison group. The study leader, Dr. JoAnn Manson at Brigham and Women's, called that "a substantial benefit," but several independent experts disagreed because of the way the study was set up to track this and certain other results.