TL;DR
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A scoping review of 157 publications found that multivitamins most consistently raised blood levels of folate and vitamins B6 and B12. Evidence of benefits for pregnancy outcomes and cognitive tests was mixed, and the review did not assess study bias or rate evidence certainty, limiting conclusions about health effects.
A scoping review of 157 publications on multivitamin trials, published in the Journal of Dietary Supplements, found that the supplements most consistently raised circulating folate and vitamins B6 and B12, but that evidence they improve health outcomes was mixed. The review examined adults and selected pregnancy studies. Its authors did not assess study bias or rate evidence certainty, limiting how firmly the findings can answer whether multivitamins make people healthier.
According to the review, researchers searched PubMed, Scopus and the Cochrane Library for peer-reviewed studies through September 9, 2026. They included trials of oral tablets or capsules containing at least 14 vitamins and minerals, with specified minimum nutrient amounts and no nutrient above its applicable upper intake limit. Eligible studies lasted at least two weeks and enrolled more than 10 participants. Most focused on adults, with an exception for some prenatal research in low- and middle-income countries.
The review reports that researchers identified 5,263 records. After screening and citation searches, they included 103 primary intervention reports and 54 related publications; some publications drew on the same trial populations. Blood measurements most consistently showed increases in vitamin B6, vitamin B12 and folate. The review found mineral responses, including those for iron, zinc and iodine, were less consistent and depended on the population, product and clinical setting.
The authors describe some trials as reporting changes in pregnancy-related outcomes or cognitive test performance, but say effects differed across groups and outcomes. In the JiVitA-3 trial, multiple micronutrients reduced low birth weight and preterm births compared with iron and folic acid, but did not significantly reduce infant mortality through six months. The SUMMIT trial reported an 18% lower relative risk of early infant mortality. These findings come from particular study settings and do not establish a broad benefit for all pregnancies or all multivitamin users.
Blood-Level Changes Are Not Health Outcomes
The review addresses a common gap between what a supplement changes in a blood test and whether that change makes a meaningful difference to health. Higher levels of selected vitamins show that the body’s measured nutrient status can respond to supplementation. They do not, by themselves, show improved memory, fewer illnesses or longer life. The review’s authors found that clinical outcomes were less consistent than nutrient-level changes.
That distinction matters to consumers because the review report says about one-third of U.S. adults take multivitamins, with use increasing with age. The authors note that a product’s formulation, a person’s baseline nutrient status and their health circumstances may all affect its effects. The review therefore does not support treating all multivitamins as interchangeable or assuming that a general supplement prevents disease.
Safety also deserves attention. The review says included trials generally described use as well tolerated in pregnancy, among older participants and after surgery, but some products caused mild digestive symptoms, particularly those containing iron or zinc. It also reports specific adverse findings in individual studies. Because safety reporting differed between trials, the review does not establish that every formulation carries the same risks.
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How the Review Set Its Scope
As described by its authors, this was a scoping review, designed to map trial evidence on broad-spectrum multivitamins rather than calculate a single pooled estimate of their effect. The researchers used Joanna Briggs Institute methodology, with two reviewers independently screening records and one checking data extracted by another. The review included studies with varied formulations, populations and durations, making the evidence broad but not uniform.
The authors did not conduct a meta-analysis, assess risk of bias or determine the certainty of evidence. Some publications also reported on the same underlying trial groups. As a result, the count of 157 publications should not be read as 157 wholly independent experiments, and the review cannot establish a precise overall benefit or confidently rank products.
Results from individual trials cited in the review illustrate why conclusions require care. A two-week study in women with preeclampsia reported improvements in proteinuria and selected maternal and neonatal outcomes when multivitamins were added to intravenous magnesium sulfate. That trial does not show that multivitamins prevent preeclampsia or benefit uncomplicated pregnancies. Likewise, a CALERIE analysis could not isolate the supplements’ effects because both randomized groups received multivitamins.
Which Benefits Hold Up Remains Unclear
The review does not settle whether multivitamins improve overall health, memory, heart health or aging outcomes. Its authors describe selected cognitive-test improvements but do not establish a consistent effect across populations or measures. The review also provides no single pooled estimate of benefit. Because the authors did not assess bias or evidence certainty, readers cannot use it alone to judge how reliable each reported result is.
The review notes that it remains unclear how much findings apply to products currently sold, since formulations vary by market and manufacturing period, as well as by life stage. People’s starting nutrient levels and medical circumstances also differ. The authors describe limits in the safety evidence: trial reporting was inconsistent, while specific reports included mild digestive complaints, modest increases in rash and nosebleeds in the Physicians’ Health Study II, gastrointestinal bleeding in COSMOS, and adverse changes in some lens-opacity subtypes in a cataract trial.
The review also flags a potential interaction between vitamin K and anticoagulants such as warfarin. People taking these medicines should consult a qualified healthcare professional before using a multivitamin. The review does not establish that the same effects or risks apply to every user or product.
More Targeted Evidence Is Needed
The review’s authors point to a need for trials that distinguish among formulations, life stages and baseline nutrient profiles, and that measure clinical outcomes as well as blood levels. They also call for better and more consistent reporting of adverse events to help clarify safety. Differences among products and participants make broad conclusions difficult to draw from the existing studies.
The source material reports no new trial, regulatory decision or change in guidance. For now, the review’s clearest conclusion is limited: multivitamins can raise certain circulating vitamin levels, while evidence of wider health benefits varies by outcome and population. Anyone considering a supplement alongside medication, particularly an anticoagulant, should discuss it with a qualified healthcare professional.
Key Questions
What did the review find most consistently?
The review found the most consistent blood-test increases were in folate and vitamins B6 and B12. Responses in mineral levels and other vitamins varied with the product, participants and clinical setting.
Does the review show that multivitamins improve overall health?
No. The review found some positive results for selected pregnancy outcomes and cognitive tests, but effects varied. Its authors did not assess study bias or rate evidence certainty, and the review did not provide a pooled estimate of overall benefit.
Did trials find any safety concerns?
The review reports that some studies found mild digestive complaints, particularly with products containing iron or zinc. Other trial reports noted specific adverse findings, but safety reporting varied, so the review does not establish a uniform risk across products.
Can multivitamins interact with warfarin?
The review notes that vitamin K may interfere with anticoagulants such as warfarin. People taking these medicines should consult a qualified healthcare professional before using a multivitamin.
Source: news-medical.net
