A scoping review of 157 clinical trial reports finds that multivitamins reliably raise blood levels of folate, vitamin B6 and vitamin B12. The authors, Z. Fan, J. M. Nelson and Taylor C. Wallace, published it in the Journal of Dietary Supplements. Their conclusion is hedged: multivitamins may support nutritional health, but effects vary by formulation and population.
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The review is a map of the literature rather than a verdict on any single pill. It pooled nothing into one effect size, and the authors state that improved nutrient levels did not consistently translate into better clinical outcomes.
The cause of the gap is simple to state. A pill can raise a number on a lab report without changing what happens to a person over years, and the review says that is what many trials show. Folate, B6 and B12 respond because the pills deliver them in doses a typical diet may not, which is a dependable effect; whether that translates into fewer strokes, fractures or cancers depends on who is taking them and what they already eat.
What the 157 reports include
Fan, Nelson and Wallace searched the Cochrane Library, Scopus and PubMed through September 9, 2026, and screened 5,263 records after removing 1,537 duplicates. The final set of 157 reports is made up of 103 primary intervention reports and 54 related publications, so the count is of reports rather than separate trials or participants. According to News-Medical’s write-up by Pooja Toshniwal Paharia, studies had to enroll more than 10 people, most enrolled adults, and the work came mainly from North America, Europe and Asia. The full text sits on the journal’s site.
Because several of the 157 reports describe the same parent trial, the 157 count overstates how many independent experiments stand behind the findings. The COSMOS cognition analyses are the clearest case: all of them come from one trial, as the review itself points out.
Blood levels rose, health outcomes were mixed
Folate, vitamin B6 and vitamin B12 showed the most consistent increases. A COSMOS biospecimen substudy also found rises in total carotenoids, lutein, beta-carotene and alpha-tocopherol, while iron, zinc and iodine results were inconsistent and depended on context. Those are biomarker results, which show that the nutrients reach the blood and say little about whether anyone is healthier.
The clinical picture is patchier. In the JiVitA-3 pregnancy trial, multiple micronutrients reduced low birth weight and preterm birth compared with iron and folic acid but did not significantly cut infant mortality through six months, while the SUMMIT trial reported an 18% lower relative risk of early infant mortality. The Physicians’ Health Study II found modest reductions in cataract and total cancer, and COSMOS did not find a significant overall cancer reduction. Both trials left overall cardiovascular prevention unestablished.
On memory, the evidence leans more positive. Mass General Brigham researchers led a meta-analysis of three COSMOS cognition studies with over 5,000 participants and estimated that a daily multivitamin slowed global cognitive aging by about two years compared with placebo; first author Chirag Vyas called the evidence strong and consistent. The Mass General Brigham announcement and the original release on EurekAlert describe the 2024 paper in the American Journal of Clinical Nutrition. The new review notes that PHS-II found no overall cognitive benefit.
Funding, limits and safety signals
The review was funded by an unrestricted educational grant from Haleon to Think Healthy Group. Wallace holds an advisory role with Haleon and is editor-in-chief of the journal that published the review; the authors report that the funder had no role in the research or the manuscript. They also did not assess risk of bias or the certainty of the evidence, and they ran no meta-analysis, so the size and reliability of any benefit cannot be read from the review.
Safety findings were mostly mild. Multivitamins were generally well tolerated in pregnancy, in older adults and after surgery, with digestive complaints mainly tied to zinc or iron. PHS-II recorded modest increases in rash and nosebleeds, COSMOS recorded increased gastrointestinal bleeding, and vitamin K may interact with warfarin.
The COSMOS results cut both ways. The trial found a modest slowing of some epigenetic aging measures, which the review says does not establish lower disease risk or longer survival, and no significant overall reduction in COVID-19 incidence. The NIH fact sheet adds that COSMOS saw no drop in total invasive cancers or cardiovascular events, though it linked multivitamin use to 38% lower lung cancer incidence, and that the U.S. Preventive Services Task Force found insufficient evidence to weigh benefits against harms.
About a third of American adults take a multivitamin, according to the NIH Office of Dietary Supplements, which concludes that these products do not appear to reliably reduce chronic disease risk. The open question the review leaves is which formulas, taken by which people with which baseline diets, produce a clinical payoff worth the price.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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