Effects of fish oil, vitamin D studied

CHICAGO — Two big studies are giving long-awaited answers on who does and does not benefit from taking fish oil or vitamin D.

Fish oil taken by healthy people, at a dose found in many supplements, showed no clear ability to lower heart or cancer risks. The same was true for vitamin D.

But higher amounts of a purified, prescription fish oil reduced heart problems and heart-related deaths among people with high triglycerides, a type of fat in the blood, and those with other risk factors for heart disease.

Doctors cheered the results and said they could suggest a new treatment option for hundreds of thousands of patients like these.

The study also tested vitamin D, which the skin makes from sun exposure. It’s tough to get enough from foods like milk, eggs and oily fish, though many foods now are fortified with it. Some studies have found that people with lower levels of vitamin D are more likely to develop cancer, but it’s not known if supplements alter that risk.

Study participants took 2,000 international units of D-3 (the most active form of vitamin D, also called cholecalciferol) or fake vitamin pills for five years.

Vitamin D did not affect the odds of having a heart attack or stroke or of developing cancer. After excluding the first two years of use, researchers saw fewer cancer deaths among those on the vitamin — 112 versus 149 in the placebo group.

“Cancer can take years to develop,” so a difference may not show up right away, study leader Dr. JoAnn Manson said. “This looks promising,” she added.

Results were announced Saturday at an American Heart Association conference in Chicago and published by the New England Journal of Medicine.

Up to 10 percent of U.S. adults take fish oil, and even more take vitamin D.