An estimated one-third of American adults and one-quarter of children and adolescents take multivitamins, with U.S. sales totaling $8 billion in 2020, according to the National Institutes of Health’s Office of Dietary Supplements.
Some experts believe a nutritious, well-rounded diet should be enough for many people. “I place my emphasis on whole foods,” says Donald D. Hensrud, associate professor of nutrition and preventive medicine at the Mayo Clinic College of Medicine. “I focus on helping my patients eat a healthy diet.”
But other experts say it is more complicated, because people often need more vitamins at certain life stages or have health conditions that make it difficult to absorb vitamins from food. Some also need supplements in addition to multivitamins.
“Some nutrients are very hard to get from food, like vitamin D, as very little occurs naturally in foods,” says Bonnie Liebman, nutrition director at Center for Science in the Public Interest (CSPI). “Many older people don’t produce enough stomach acid to extract natural vitamin B-12 from milk, meat or eggs. Vitamin B-12 deficiency can cause irreversible nerve damage and can mimic dementia — something you want to avoid.”
Scientists who study multivitamins say there is growing evidence that multivitamins also can convey additional health benefits, including a delay in cognitive decline among older people. A recent three-year study of more than 2,200 participants 65 and older funded by the National Institute on Aging, for example, found that those taking a daily multivitamin demonstrated significant cognitive improvement in abilities that tend to decline with normal aging, including short-term memory and such executive functions as decision-making, when compared with those who received a placebo.
The unpublished results, which were presented at a scientific meeting in the fall, showed that multivitamin-takers demonstrated only 1.2 years of mental decline, rather than three years. Put another way, they preserved 1.8 years — almost 60 percent — of their mental sharpness. The research was part of a larger trial that looked at the effects of multivitamins on cancer. The cognition results are expected to be published soon.
The larger study, known as the COcoa Supplement and Multivitamin Outcomes Study, or COSMOS, began in 2014 to try to replicate the findings of an earlier trial, the Physicians’ Health Study II, which ran from 1997 through 2011. PHS II saw an 8 percent reduction in total cancers among those 50 and older who took daily multivitamins, but — unlike COSMOS — did not show any cognitive benefits. The COSMOS study, on the other hand, which ran only 3½ years, did not find a drop in cancers.
But the researchers — the same in both studies — stress that differences in the design and length of the two studies account for the seemingly contradictory results.
“COSMOS was just not long enough to tease out the cancer effects,” says Howard Sesso, associate professor of medicine at Harvard Medical School and one of the investigators. “For cancer, you really need more time to detect the impact of nutritional interventions. We are following up with…
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