Could supplements do more harm than good?

red and yellow capsules

Many vitamins, supplements and dietary interventions do not seem to help people live longer or stave off heart disease, according to a US review of studies

A new evidence review suggests that few nutritional supplements or dietary interventions offer any protection against cardiovascular disease or death, and some may actually cause harm.

Findings from the analysis, published in the Annals of Internal Medicine, included that only a few of the supplements and dietary interventions studied had clear evidence to support a role in reducing death and cardiovascular events.

Current US dietary guidelines recommend several healthy eating patterns, including Mediterranean and vegetarian diets, but they do not recommend routine supplement use to reduce the risk for cardiovascular disease or other chronic diseases. Nonetheless, half of Americans use some form of supplements with the reported goal of improving their overall health.  

Researchers from West Virginia University analyzed 277 randomized controlled trials comprising nearly a million people to determine the effects of 16 different nutritional supplements and eight dietary interventions on mortality and cardiovascular outcomes in adults.

The researchers found some evidence that reduced salt intake was protective for all-cause mortality in participants with normal blood pressure and that omega-3, long-chain fatty acids were protective for myocardial infarction and coronary heart disease.

Folic acid showed some protective benefit for stroke.

Conversely, combined calcium plus vitamin D intake increased the risk for stroke. Other supplements, such as multivitamins, selenium, vitamin A, vitamin B6, vitamin C, vitamin E, vitamin D alone, calcium alone, folic acid, and iron, or such dietary interventions as the Mediterranean diet, reduced saturated fat intake, modified fat intake, reduced dietary fat intake, and increased intake of fish oil supplements, did not seem to have significant effect on mortality or cardiovascular outcomes.

According to the authors of an accompanying editorial from Scripps Research Translational Institute, the findings are limited by the quality of the evidence.

For example, geographic considerations among the studies need to be considered.

The reported benefit of folate seemed to be largely driven by the inclusion of one study from China, where a folate-rich diet is not routine.

 In addition, most studies rely on food diaries, which are based on a person’s memory of what they consumed and therefore are not wholly reliable. The authors say that for now, it is reasonable to hold off on using supplements or diet modification for the purpose of cardiovascular disease prevention in all guidelines and recommendations.

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