A multivitamin covers your nutritional gaps

A multivitamin narrows many nutrient gaps and leaves some open. In national diet surveys, counting a multivitamin lowers the share of adults whose intake falls below the average requirement for most vitamins and minerals, and in randomized trials blood levels of several vitamins rise compared with a placebo. Shortfalls in vitamin D, calcium, magnesium and potassium remain common even when multivitamins are counted, and some users end up above the upper intake level for nutrients such as iron, folic acid and zinc.

The people in these surveys are not a random slice. Supplement users already get more of several vitamins from food than non-users do, and in lower-income adults supplement use closed fewer gaps than in higher-income adults. The surveys count nutrients on paper, from diet recalls and product labels. About 20 randomized trials have measured blood levels instead; the two largest, with about 400 people each and lasting two and about nine years, found higher levels of several vitamins with a multivitamin than with a placebo. These two trials enrolled healthy, mostly older adults who were not chosen for having a shortfall, so they show that vitamin levels rise rather than that a particular person's gap closes. One 2026 trial did choose adults with low vitamin levels, and it is described below.

In US survey data from 2009 to 2012, 2,623 adults took a multivitamin. Counting the product alongside their food, the share below the average requirement fell from 93 to 17 percent for vitamin D, from 80 to 6 percent for vitamin E, from 43 to 22 percent for magnesium and from 38 to 20 percent for calcium, and was under 5 percent for the other nutrients examined. No more than about 4 percent went above an upper level for any nutrient. That analysis, and a companion analysis of the same data by income, was funded by supplement manufacturers. In earlier US data from 2003 to 2006, covering 8,860 adults, supplement use lowered the share below the requirement for every vitamin examined and raised the share above the upper level for folic acid and vitamins A, B6 and C. In US data from 2007 to 2010, covering 16,444 people aged 4 and over, about half took a multivitamin; with food and multivitamins both counted, 74 percent of that whole population was still below the requirement for vitamin D, 67 percent for vitamin E, 46 percent for magnesium and 39 percent for calcium, and the share above the adequate intake for potassium was reported as 0 percent. Those figures combine users and non-users.

Among 76,925 French adults, supplement use of any kind lowered the prevalence of inadequate intake compared with diet alone, with reported reductions of 19 percent for calcium in women and 11 percent for vitamin C in men among the largest, and produced intakes above the upper level for iron in 6 percent of men and 9 percent of women. Who benefits varies. In the US data from 2009 to 2012, supplement use lowered inadequacy for 10 of 17 nutrients in higher-income adults but for only 4 or 5 of 17 in poor and near-poor adults. In a small Slovenian study of 130 adults on vegan, vegetarian, low-carbohydrate and omnivorous diets, multi-nutrient products raised intake of B vitamins but did not bring vitamin D, potassium, calcium or iodine to adequate levels, while several nutrients that were already adequate were supplemented anyway.

The trials measured blood levels directly. In an Italian trial of 1,020 people aged 55 to 75, a multivitamin taken for about nine years raised blood vitamin E, beta-carotene, folate and vitamin B12 and improved riboflavin status in the 407 who were retested, compared with a placebo, and the rise in vitamins A, C and E was larger in people who started lower. In a US trial of older adults, 399 who gave blood samples over two years had higher vitamin E and several carotenoids on a multivitamin, while four other carotenoids did not change. In a small US trial of 35 healthy men over 67, several vitamin levels rose over at least six months and none of the five minerals measured changed significantly. In a 2026 trial in China, 155 adults aged 18 to 65 were chosen for a low blood level of vitamin A, D or E. All were given nutrition advice, and half also took a multivitamin made mainly of those three vitamins for four weeks. Blood levels of all three vitamins rose in both groups, and the share of people still low fell in both (for vitamin D, from 35 to 0 percent with the multivitamin and from 35 to 4 percent without). The two groups did not differ significantly at four weeks.

Part of the pattern follows from what the products contain. The NIH Office of Dietary Supplements notes that multivitamins often have small amounts of calcium, magnesium and potassium, and that the Food and Nutrition Board, which sets intake targets, does not address whether supplements can make up for a shortfall in the diet. The fact sheet's section on interactions notes that vitamin K decreases the effectiveness of warfarin and similar drugs. Pregnancy sits outside most of this evidence, and prenatal multivitamins are formulated differently.