The latest word on two of the most popular dietary supplements is a weighty one: Brigham and Women’s Hospital researchers over the weekend released the results of the largest randomized clinical trial to evaluate the effects of vitamin D and omega-3 fatty acid supplements on heart attack, stroke, and cancer risk. The study found that omega-3 fatty acids or fish oil cut heart attack risk.

The study, presented at the AmericanAssociation’sation’s annual conference and published simultaneously in the New England Journal of Medicine, was conducted as a rigorous placebo-controlled trial over more than five years and revealed what researchers cal”ing a “treasure” trove” of information on the effects of both supplements, though not all of it was positive.

Specifically, the study showed that taking omega-3 fatty acids, aka fish oils, reduced the risk of heart attack but did not affect the risk of stroke or cancer.

Vitamin D supplements, on the other hand, did not affect heart attack, stroke, or cancer incidence, according to the study. However, one promising secondary finding was that vitamin D was associated with decreased cancer deaths, which kicked in at least two years after participants began taking it. That is, taking sometstudy’ske the study’s 2,000 IU dosewon’titamin D won’t stop you from getting cancer, but it appears to possibly reduce your risk of dying from it by about 25 percent.Fish Oil May Help Prevent Heart Attacks

Fish oil did not pass the test of reducing cardiovascular events overall because it did not lessen a combined measure of heart attack and stroke risk. However, the study lowered the risk of heart attack alone by 28 percent (40 percent for those who habitually consumed little fish in their diet) and decreased the risk of a fatal heart attack by 50 percent.

For one group, results were even more pronounced: African American participants who took fish oils saw a 77 percent reduction in heart attack risk —  the study’s author, JoAnn Manson, chief of the Division of Preventive Medicine Women and Women’s Hos”ital, ca”led “dramatic” for a population that has not been well studied in previous trials of such”supplements. “If this finding is confirmed and replicated, it may point to an auspicious approach to reducing coronary risk among Afri”Americans,” Manson said in a statement.

Overall, the study included 25,871 men and women age 50 and older from across the U.S., including 5,106 African Americans, who had no history of cancer, heart attack, stroke, or other forms of cardiovascular disease when they enrolled. That detail made the research the first to look at how these supplements might prevent the first occurrence of heart disease in a general population. (Earlier trials had examined whether fish oil or other supplements might prevent heart attack or stroke in patients with either a history of heart disease or a very high risk of it.)