Some popular vitamin and mineral supplements could even increase the risk of death, scientists claim. Their research concludes only folic acid is proven to reduce risks of heart disease or stroke.
2018 Study Abstract
The authors identified individual randomized controlled trials from previous meta-analyses and additional searches, and then performed meta-analyses on cardiovascular disease outcomes and all-cause mortality. The authors assessed publications from 2012, both before and including the U.S. Preventive Service Task Force review. Their systematic reviews and meta-analyses showed generally moderate- or low-quality evidence for preventive benefits (folic acid for total cardiovascular disease, folic acid and B-vitamins for stroke), no effect (multivitamins, vitamins C, D, β-carotene, calcium, and selenium), or increased risk (antioxidant mixtures and niacin [with a statin] for all-cause mortality). Conclusive evidence for the benefit of any supplement across all dietary backgrounds (including deficiency and sufficiency) was not demonstrated; therefore, any benefits seen must be balanced against possible risks.
Since the 2013 to 2014 assessment and report of the USPSTF, the most notable finding was the effect of folic acid in reducing stroke and CVD, with significance driven by the 5-year 20,000 Chinese CSPPT RCT, which was supported by the reduction in stroke seen in RCTs of B-complex vitamins in which folic acid was a component. Vitamin B3 (or niacin) might increase all-cause mortality, which was possibly related to its adverse effects on glycemic response. Antioxidant mixtures did not appear to benefit CVD but might increase all-cause mortality. Although sufficient studies on vitamin D exist, to be confident that there is no all-cause mortality effect, further studies on multivitamins, the most commonly used supplement, may still be useful, because of the marginal benefit seen in our analysis. In the absence of further studies, the current data on supplement use reinforce advice to focus on healthy dietary patterns, with an increased proportion of plant foods in which many of these required vitamins and minerals can be found.