Few nutritional supplements or dietary interventions offer any protection against cardiovascular disease or death, and some may actually cause harm, an evidence review suggested.
To examine evidence about the effects of nutritional supplements and dietary interventions on mortality and cardiovascular outcomes in adults, researchers reviewed 277 trials, with 24 interventions and 992,129 participants. A total of 105 meta-analyses were generated to determine the effects of 16 nutritional supplements and eight dietary interventions on mortality and cardiovascular outcomes in adults. Study results were published by Annals of Internal Medicine on July 9.
Researchers found moderate-certainty evidence that reduced salt intake was protective for all-cause mortality in normotensive participants (risk ratio [RR], 0.90; 95% CI, 0.85 to 0.95) and cardiovascular mortality in hypertensive participants (RR, 0.67; 95% CI, 0.46 to 0.99). Low-certainty evidence showed that long-chain polyunsaturated fatty acid (LC-PUFA) consumption was associated with reduced risk for myocardial infarction (RR, 0.92; 95% CI, 0.85 to 0.99) and coronary heart disease (RR, 0.93; 95% CI, 0.89 to 0.98). Folic acid was associated with lower risk for stroke (RR, 0.80; 95% CI, 0.67 to 0.96; low certainty), whereas calcium plus vitamin D was associated with increased risk for stroke (RR, 1.17; 95% CI, 1.05 to 1.30; moderate certainty).
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 a significant effect on mortality or cardiovascular outcomes.
The authors of both the study and an accompanying editorial noted that the findings are limited by the quality of the evidence. For example, geography is an issue; the reported benefit of folate seems to be largely driven by the inclusion of one study from China, where a folate-rich diet is not routine. In addition, most studies used food diaries, which are not wholly reliable.
“Unfortunately, the current study leaves us with the same foggy conditions that we started with,” the editorial stated. “Until these conditions clear, it would be reasonable to hold off on any supplement or diet modification in all guidelines and recommendations.”