REUTERS / Shannon Stapleton
Three out of four American adults consume some kind of dietary supplement, and global sales of these products are expected to reach $ 300 billion over the next five years.
Nutritional supplements and dietary interventions offer no protection against cardiovascular disease and early death, according to a major new analysis of dozens of studies on the subject, published Monday in the Annals of Internal Medicine.
The only possible exceptions were a low salt diet and two supplements – folate (folic acid) and omega-3 fatty acids (fish oil). But even in these cases, the evidence supporting their benefits was weak.
The study also revealed – with moderate certainty – that simultaneous intake of vitamin D and calcium supplements was associated with an increased risk of stroke.
"Do not waste your money with these over-the-counter multivitamins and nutritional supplements because if you use them with the belief that they will reduce your mortality or improve your cardiovascular health, they do not do it," Safi Khan said. . , lead author of the study and assistant professor at the Faculty of Medicine at the University of West Virginia, in an interview with Bloomberg News.
As the basics of the study point out, three out of four American adults consume some kind of dietary supplement, and global sales of these products are expected to reach $ 300 billion over the next five years.
The use of dietary supplements continues to progress, although their safety remains uncertain. Several studies have shown that they can be harmful.
Evidence supporting (or against) health claims of various specific dietary interventions, such as reducing saturated fat or salt content or increasing fish consumption, are also ambiguous.
Little or no impact
For their study, Khan and his colleagues conducted a meta-analysis of 277 randomized controlled trials (considered the gold standard for medical research), which examined the effects of 16 nutritional supplements and eight dietary interventions on cardiovascular disease. and premature deaths from all causes. . More than one million people participated in these trials.
The analysis revealed that most supplements, including multivitamins, calcium, iron, selenium and vitamins A, B6, C, D and E, had no impact on cardiovascular health nor on mortality. Eating omega-3 fatty acid supplements was associated with a reduced risk of heart attack, and taking folic acid supplements was associated with a reduced risk of stroke. The evidence supporting both of these benefits, however, was "low certainty".
As an editorial accompanying the study points out, the results for omega-3 fatty acid supplements are strongly contradicted by several recent randomized controlled trials that did not find that the products presented cardiovascular benefits. "The results of these tests would tend to degrade at best the degree of uncertainty associated with omega-3 fatty acid supplements," write the authors of the editorial, Drs. Eric Topol and Amitabh Pandey of the Scripps Research Translational Institute in La Jolla, California.
The positive results for folic acid are also problematic, as they stem mainly from a study in China, where "a diet rich in folate is not a routine".
In the United States, foods are systematically fortified with folic acid. It is therefore unlikely that Americans will get the same benefits as Chinese people by taking folic acid supplements.
The meta-analysis found somewhat stronger evidence that supplements containing both calcium and vitamin D were associated with an increased risk of stroke. This finding supports a 2016 study by Johns Hopkins University that taking calcium supplements (without eating calcium-rich foods) can increase the risk of developing atherosclerosis, a potentially dangerous build-up. of plaques in the arteries.
It is not certain that this increased risk results from taking supplements alone or from what Topol and Pandey describe as "overeating": taking supplements as part of a Western diet already fortified with calcium plus vitamin D For example, cereals, for example, are often fortified with one or other of these nutrients.
The meta-analysis also revealed no solid evidence indicating that eating less fat, including saturated fats – or even following the much touted (but controversial) Mediterranean diet – had no impact on cardiovascular outcomes or mortality. Of the eight dietary interventions examined in the meta-analysis, only a low salt diet appears to influence cardiovascular health. But the evidence to support this diet was weak.
"Unfortunately, this study leaves us with the same fog conditions that we started with," say Topol and Pandey. "Until these conditions are met, it would be reasonable to suspend any dietary supplement or modification in all directives and recommendations."
IMF: You will find summaries of the meta-analysis and the accompanying editorial on the Annals of Internal Medicine website, but the full articles are behind a paying wall.