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Vitamin D And Fish Oil Supplements Mostly Disappoint In Long-Awaited Research Results

Taking fish oil supplements to prevent cardiovascular disease and cancer may not be effective, a new study suggests.
Cathy Scola
Getty Images
Taking fish oil supplements to prevent cardiovascular disease and cancer may not be effective, a new study suggests.

Many people routinely take nutritional supplements such as vitamin D and fish oil in the hopes of staving off major killers like cancer and heart disease.

But the evidence about the possible benefits of the supplements has been mixed.

Now, long-awaited government-funded research has produced some of the clearest evidence yet about the usefulness of taking the supplements. And the results — published in two papers — are mostly disappointing.

"Both trials were negative," says Dr. Lawrence Fine, chief of the clinical application and prevention branch of the National Heart, Lung, and Blood Institute, a part of the National Institutes of Health, which funded the studies.

"Overall, they showed that neither fish oil nor vitamin D actually lowered the incidence of heart disease or cancer," Fine says.

The results were presented at the American Heart Association Scientific Sessions in Chicago and released online Saturday by The New England Journal of Medicine. One paper focused on vitamin D supplementation, and the other focused on fish oil.

The trials involved nearly 26,000 healthy adults age 50 and older with no history of cancer or heart disease who took part in the VITAL research project. Twenty percent of the participants were African-American.

Some of the participants took either 1 gram of fish oil — which contains omega-3 fatty acids — plus 2,000 international units of vitamin D daily. Others consumed the same dose of vitamin D plus a placebo, while others ingested the same dose of fish oil plus a placebo. The last group took two placebos. After more than five years, researchers were unable to find any overall benefit.

While the overall results were disappointing, there appeared to be a beneficial effect when it came to one aspect of heart disease and fish oil: heart attacks.

A secondary analysis showed taking fish oil lowered the risk of heart attack by about 28 percent, which is a "statistically significant" finding, says Dr. JoAnn Manson, who is chief of the division of preventive medicine at the Brigham and Women's Hospital in Boston. She led the research.

Those who appeared to benefit the most were people who didn't ordinarily eat much fish in their day-to-day diet, as well as African-Americans, Manson says.

African-Americans in the study experienced a 77 percent lower risk of heart attack compared with taking a placebo, which is a "dramatic reduction," Manson says. Further research is needed to confirm these findings, she adds, but, "in the meantime, it would be reasonable for African-Americans to talk with their health care providers about whether they may be candidates for taking fish oil supplements."

In an editorial also published in the New England Journal of Medicine, authors Dr. John F. Keaney and Dr. Clifford J. Rosen take issue with some of the analysis in the study and write that the positive findings about heart attacks and African-Americans and individuals who don't eat much fish need to be interpreted with caution.

There were no serious side effects, such as bleeding, high blood calcium levels or gastrointestinal symptoms found with either supplement.

Manson and her colleagues plan to further analyze their data and look for possible links between vitamin D and fish oil and cognitive function, autoimmune disease, respiratory infections and depression. Earlier research suggests the supplements may have some benefit for these conditions.

In the meantime, NIH official Lawrence Fine says, don't throw out your fish oil and vitamin D.

"At this point, if one is thinking about supplementation, either omega-3s or vitamin D, talking to your physician or health care provider is the next step," Fine says.

Fine and Manson stressed that vitamin D and the omega-3 fatty acids found in fish oil are important nutrients, but that the best way to get them is as part of a well-balanced diet. That includes eating fatty fish like sardines, tuna and salmon, and vitamin D-fortified cereals, milk and orange juice.

Another study presented at the same meeting examined whether a substance derived from a component of fish oil, known as icosapent ethyl, might reduce adverse events among people who already have cardiovascular risk factors, such as hardening of the arteries, diabetes or high blood fats known as triglycerides.

Overall, that study found there was a 25 percent risk reduction for patients taking the extract. These patients were less likely to die from heart disease, have a heart attack or stroke, be hospitalized for chest pain or need procedures such as angioplasty, stenting or bypass surgery, researchers reported.

"We are reporting a remarkable degree of risk reduction," says Dr. Deepak Bhatt, who headed the study and is a cardiologist at Brigham and Women's Hospital.

The study, which was also a randomized clinical trial, tracked participants for an average of five years. The volunteers took icosapent ethyl, which is sold under the brand name Vascepa and was developed by the Amarin Corporation, which funded Bhatt's research.

The product is available by prescription only for patients with high triglycerides. But the company is expected to apply for FDA approval within the next year to expand treatment to include all high-risk cardiovascular patients.

Copyright 2020 NPR. To see more, visit https://www.npr.org.

Award-winning journalist Patti Neighmond is NPR's health policy correspondent. Her reports air regularly on NPR newsmagazines All Things Considered, Morning Edition, and Weekend Edition.