It is well known within the research community that dietary supplements as a class achieve next to nothing for basically healthy people, those lacking any specific deficiency or medical condition that might cause that deficiency. In fact the evidence strongly suggests that some supplements, antioxidants for example, may even be modestly harmful over the long term. This scientific consensus has to compete with the marketing budget of the supplement industry, which seems to be doing fairly well for a community focused on selling a mix of largely useless and mildly harmful products. So studies such as this one continue to roll out, and perhaps one day there will be meaningful change as a result, but I'm not holding my breath.
Treatment and prevention of micronutrient deficiencies with vitamins and minerals in the last two-and-a-half centuries are among the most dramatic achievements in the history of nutritional science. However, interest in micronutrients has shifted recently from prevention of classic deficiency states to prevention of possible subclinical deficiencies and promotion of overall health and longevity using supplemental vitamins and minerals (supplement use). Here, the data are less clear, but supplement use is widespread.
Using the National Health and Nutrition Examination Survey data (1999 to 2012) on 37,958 adults, it was estimated that supplement use was high in 2012, with up to 52% of the population taking supplements. Multivitamins were taken by 31% of the population, vitamin D by 19%, calcium by 14%, and vitamin C by 12%. Despite high supplement use by the general public, there is no general agreement on whether individual vitamins and minerals or their combinations should be taken as supplements for cardiovascular disease (CVD) prevention or treatment.
We conducted a systematic review and meta-analysis of existing systematic reviews and meta-analyses and single randomized controlled trials (RCTs) published in English from 2012 to 2017. Where both supplements and dietary intakes of nutrients in foods were combined as total intakes, data were not used unless supplement data were also presented separately. We assessed those supplements previously reported on by the US Preventive Services Task Force (USPSTF): vitamins A, B1, B2, B3 (niacin), B6, B9 (folic acid), C, D, and E, as well as β-carotene, calcium, iron, zinc, magnesium, and selenium.
The following supplements were associated with no significant effect on CVD outcomes and all-cause mortality: vitamins A, B6, and E; β-carotene; zinc; iron; magnesium; selenium; and multivitamins. In general, the data on the popular supplements (multivitamins, vitamin D, calcium, and vitamin C) show no consistent benefit for the prevention of CVD, myocardial infarction, or stroke, nor was there a benefit for all-cause mortality to support their continued use. At the same time, folic acid alone and B-vitamins with folic acid, B6, and B12 reduced stroke, whereas niacin and antioxidants were associated with an increased risk of all-cause mortality. Overall, the effects were small; the convincing lack of benefit of vitamin D on all-cause mortality is probably the reason for the lack of further studies published since 2013. The effects of folic acid in reducing stroke is also convincing, with a 20% reduction.