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Vitamin D and fish oil supplements do not prevent heart disease or cancer, large clinical trial finds

Dietary supplements are a multibillion-dollar industry in the United States, and both vitamin D and fish oil have been hyped as preventive cures for a host of medical ailments.

Vitamin D
Vitamin D tests are now the fifth most common lab test ordered by doctors for Medicare patients.

On Saturday, Harvard researchers reported the long-awaited results from a large randomized, double-blinded, placebo-controlled clinical trial on the effects of vitamin D and omega-3 fatty acid (“fish oil”) supplements on the development of cardiovascular disease and cancer.

Neither supplement was found to offer protection against those diseases.

These findings offer yet more evidence that dietary supplements have been overhyped and oversold.

“Most people buying supplements are giving themselves very expensive urine,” Dr. Naveed Sattar, a professor of cardiometabolic medicine at the University of Glasgow, told The Independent. “They’re wasting their time and getting false reassurance of protection from these supplements, when what they need is help to look at improving their lifestyles in ways which are enjoyable and sustainable.”

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The new findings were presented Saturday at an American Heart Association meeting in Chicago and published online that same day in two papers in the New England Journal of Medicine (NEJM). They come on the heels of another major study that examined dozens of clinical trials and concluded that vitamin D supplements do nothing to protect people from bone fractures or falls.

Study details

For the Harvard study, known as the Vitamin D and Omega-3 Trial (VITAL), the researchers recruited 25,871 healthy U.S. adults aged 50 and older who had no history of heart disease or cancer (except non-melanoma skin cancer). The participants were randomly assigned to four different groups. One group took 1 gram of fish oil (which contains omega-3 fatty acids) and 2,000 international units (IUs) of vitamin D. A second group took just the fish oil, while a third took only the vitamin D. The fourth group took two placebo pills.

The participants were followed for up to six years. At the end of that period, there was no statistically significant difference among the four groups regarding their rates of major cardiovascular events (heart attacks, strokes and cardiovascular-related deaths). The same was true for their rates of diagnosed cancers.

When the researchers broke down the data by type of cardiovascular event, they did find that the fish oil supplements were associated with a 28 percent reduction in the risk of a heart attack and 50 percent reduction in the risk of a fatal heart attack, primarily among people who didn’t eat much fish in their daily diet and among African-Americans. But that was a secondary, rather than a primary endpoint, of the study, and therefore must be interpreted with caution, say the study’s authors. That’s because secondary endpoints do not carry the same statistical weight as primary ones and are more likely to be due to chance.

As an omega-3 researcher not involved in the VITAL study told a reporter for the Cardiovascular Research Foundation, “to drill down into the secondary endpoints is of some concern because I think there is often the risk of getting spurious results.”

A third paper, published in the same issue of NEJM, reported that a fish-oil-derived drug (a highly concentrated, prescription-strength form of eicosapentaeic acid) reduced the risk of dying from a heart attack or stroke in people at high-risk for cardiovascular disease by 25 percent. But, as Forbes reporter Matthew Harper points out, cardiologists not involved with the study say those results come with a huge caveat: “the placebo that was given in the study [which contained mineral oil] appears to have caused blood test changes that might have caused heart attacks, potentially exaggerating the [fish-oil] medicine’s effectiveness.”

So, the results of that study — known as the REDUCE-IT trial — are far from definitive.

Not surprising

Dietary supplements are a multibillion-dollar industry in the United States, and both vitamin D and fish oil have been hyped as preventive cures for a host of medical ailments, despite a lack of high-quality evidence.

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Testing for vitamin D levels has also become a big source of income for commercial laboratories. Vitamin D tests are now the fifth most common lab test ordered by doctors for Medicare patients.

Whether the results from the VITAL randomized, controlled clinical trial — a type of study considered the “gold standard” for evaluating the effectiveness of a medical treatment — will change consumers’ behavior remains unclear.

But they should, as many experts have noted over the weekend.

“At the end of the day the results now reported show that vitamin D did not reduce the risk of cancer and did not reduce the risk of heart disease,” said Dr. Steven Nissen, who is chairman of cardiovascular medicine at the Cleveland Clinic and who was not involved in the NEJM studies, in a video interview with MedPage Today. “So, as many of us feared, this cult of vitamin D use turned out not to be an effective approach to preventing disease. And it’s a warning that this widespread use of dietary supplements without good scientific evidence can lead us to make mistakes.”

“Similarly, the fish oil study also did not show a benefit on heart disease or on cancer for the primary endpoints,” he added. “There was a suggestion of a reduction in [heart attacks] with fish oil, but it was a component of the primary endpoint. It’s difficult to interpret results when looking at a component of the endpoint. It would be considered a hypothesis-generating result, not definitive proof.”

FMI: You’ll find the two papers on the VITAL trial and the paper on the REDUCE-IT trial on the NEJM website.