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Trial concludes vitamin D and fish oil don’t lower incidences of heart disease or cancer

The findings of one of the largest placebo-controlled trials into the beneficial effects of vitamin D and fish oil ever conducted have just been published and, despite some hyperbolic media releases, the overall results found both supplements were no better than the placebo in lowering incidences of cancer or heart disease.

Both omega-3 fish oil and vitamin D supplements have been found to be no better than a placebo in preventing cancer or cardiovascular events(Credit: stocksnapper/Depositphotos)

The rigorous and well designed trial started with over 25,000 healthy subjects over the age of 50. Each participant was randomly, and blindly, assigned one of four daily combinations: 2,000 units of vitamin D and 1 gram of fish oil, the vitamin D and a placebo, the fish oil and a placebo, or two placebos.

The study followed the subjects for over five years, tracking the onset of major cardiovascular events or invasive cancers, and the results will certainly disappoint anyone with a stake in these supplements. The conclusion of the omega-3 study was, “Supplementation with n−3 fatty acids did not result in a lower incidence of major cardiovascular events or cancer than placebo.” The conclusion of the vitamin D study was pretty much the same, “Supplementation with vitamin D did not result in a lower incidence of invasive cancer or cardiovascular events than placebo.”

However, digging into the more granular detail in the study reveals some specific findings that some researchers are pushing to the foreground. JoAnn Manson, one of the key researchers on the study, focuses on two specific secondary datapoints suggesting, “omega-3s were associated with a reduction in risk of heart attacks across our study population, especially among participants who had lower than average fish intake,” and vitamin D could be associated with lower rates of cancer deaths starting from one to two years into the study.

In an editorial accompanying the dual studies, published in the New England Journal of Medicine, John F. Keaney and Clifford J. Rosen suggest “these “positive” results need to be interpreted with caution. As well as noting, in regards to the fish oil conclusion, that these positive results have not been consistently observed across other large omega-3 trials, Kearney and Rosen offer a reminder that, “medical literature is replete with exciting secondary end points that have failed when they were subsequently formally tested as primary end points in adequately powered randomized trials.”

Jane Armitage, from the University of Oxford, also questions the veracity of some of these secondary conclusions, suggesting while “they did see fewer heart attacks among those taking the fish oils,” there was also no overall effect seen on all other cardiovascular events, so this needs to be interpreted cautiously.

In many ways this research seems to be a perfect litmus test in how problematic the reporting of scientific research can be. The headline on the research from the Washington Post is, “Fish-oil drugs protect heart health, two studies say,” while the New York Times reports the exact same research with the headline, “Vitamin D and Fish Oils Are Ineffective for Preventing Cancer and Heart Disease.”

Neither headline is specifically incorrect, however it may be slightly disingenuous to concentrate on a particular study’s secondary effect when the overall primary finding was negative. The press release from Brigham and Women’s Hospital does nothing to avoid such cherrypicking, leading with the subtitle “Findings show omega-3 fatty acids reduced risk of heart attacks, especially among African Americans; vitamin D reduced cancer deaths over time.”

Again, these statements are not technically incorrect, but they are certainly not in line with the researcher’s own published journal conclusions that clearly state both high-dose vitamin D and omega-3 supplementation do not reduce the incidence of cancer or major cardiovascular events.

Source:, by Rich Haridy

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