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A scoping review published in the Journal of Dietary Supplements examined 157 publications and found that multivitamins most consistently raised blood levels of folate and vitamins B6 and B12. Some trials reported benefits for pregnancy outcomes or cognitive tests, but results varied. The authors did not assess evidence quality or pool results, limiting conclusions about health benefits.
A scoping review of 157 publications on multivitamin trials, published in the Journal of Dietary Supplements, found the supplements most consistently raised circulating folate and vitamins B6 and B12. The review reported mixed findings on whether those changes improve health. Its authors said they did not assess study quality or combine results in a meta-analysis.
According to the review’s methods, researchers searched the Cochrane Library, Scopus and PubMed for peer-reviewed studies published through September 9, 2026. Eligible studies tested oral tablets or capsules with at least 14 vitamins and minerals, each supplying at least half of the relevant U.S. recommended intake or adequate intake, and ran for at least two weeks. The review included 103 primary intervention reports and 54 related publications; some publications used the same trial populations.
In its summary of trial findings, the review said blood measurements most consistently showed increases in vitamin B6, vitamin B12 and folate. Responses to minerals, including iron, zinc and iodine, depended on the circumstances. Some included studies reported improvements in pregnancy-related outcomes or cognitive test performance, but effects varied among groups and endpoints. The authors cautioned that the review does not establish that raising nutrient levels alone improves health.
The review described tolerability as generally favorable in pregnancy, older participants and people recovering from surgery, while noting that safety findings were not uniform. Some included studies reported mild digestive symptoms, especially with products containing iron or zinc. The authors also noted that the Physicians’ Health Study II reported modest increases in rash and nosebleeds, while COSMOS reported more gastrointestinal bleeding. They said differences in safety reporting made comparisons difficult.
Nutrient Gains Do Not Settle Health Benefits
The source report notes that about one-third of U.S. adults take multivitamins, with use increasing with age. The review suggests supplements can change levels of some nutrients, but the authors distinguish those biological changes from proof of fewer illnesses, better memory or longer life.
For readers, the distinction is practical: as the review’s findings indicate, a product’s effects can depend on its formulation, a person’s baseline nutrient status and life stage. A broad supplement may not address a specific deficiency or produce the same outcome across people. The authors’ stated limitations also mean the review cannot rank products or provide a reliable estimate of the size of any health benefit.
The review authors noted a safety consideration for people using warfarin and other anticoagulants: vitamin K in multivitamins may interfere with these medicines. Anyone taking anticoagulants or considering supplements for a health concern should discuss the choice with a qualified healthcare professional.
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How Researchers Defined Multivitamins
For this review, the researchers defined multivitamins as broad-spectrum oral products containing at least 14 vitamins and minerals, with at least two vitamins and two minerals, and no nutrient above its applicable upper intake limit per daily serving. They excluded products such as fortified foods, syrups, powders, sprinkles and enteral nutrition. The authors said this definition means their conclusions do not necessarily apply to every product marketed as a multivitamin.
The review reports that, of 5,263 records identified, the team removed 1,537 duplicates and screened the remaining records, ultimately including 157 publications, four found through citation searches. Studies came mainly from North America, Europe and Asia. The authors described their work as a scoping review intended to map trial findings rather than estimate one overall effect.
The review cites individual trials to illustrate why outcomes need careful interpretation. In JiVitA-3, 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 results come from particular trial settings and, as the review cautions, are not evidence that all multivitamins prevent adverse pregnancy outcomes.
Evidence Gaps Limit Conclusions
The review authors did not assess risk of bias or certainty of evidence and did not conduct a meta-analysis. They said the review maps reported findings but does not determine how dependable they are overall or calculate a pooled estimate of benefit. The review also includes related reports from some of the same trial populations, rather than 157 entirely separate trials.
The authors said it remains unclear which formulations, doses or user groups, if any, are most likely to gain a meaningful clinical benefit. Findings in the reviewed studies varied with baseline nutrient status, setting and outcome measured. The review also notes that safety information was inconsistently reported; its findings do not establish a general benefit for memory, heart health or aging.
The review’s account of individual results also calls for caution. A two-week study in women with preeclampsia reported improvements in proteinuria and selected maternal and newborn outcomes when multivitamins were added to intravenous magnesium sulfate. That result does not show that multivitamins prevent preeclampsia or benefit uncomplicated pregnancies. The supplied report ends before completing its description of a 12-week older-adult trial, so its primary result cannot be summarized here.
What Future Trials Need to Clarify
Based on limitations identified in the review, future studies could distinguish the effects of specific formulations and populations, track clinical outcomes as well as blood nutrient levels, and report adverse events consistently. The authors’ concerns about study quality and the lack of pooled results also point to the value of better assessments of evidence quality and certainty.
The review offers no new clinical recommendation or single conclusion that multivitamins improve health for adults generally. Its authors point to the need for clearer, comparable trials; for individual decisions, people should discuss their circumstances and medicines with a qualified healthcare professional.
Key Questions
What did the review find multivitamins most consistently changed?
The scoping review found the most consistent increases in circulating folate and vitamins B6 and B12. Changes in other nutrients, including minerals, varied across studies and participants.
Did the review show that multivitamins improve overall health?
No general improvement was established by the review. Some included trials reported pregnancy-related or cognitive outcomes, but findings varied. The authors also did not assess risk of bias or certainty of evidence and did not pool results.
Were there reported side effects?
The review reported that some studies found mild digestive complaints, particularly with products containing iron or zinc. It also noted that the Physicians’ Health Study II reported modest increases in rash and nosebleeds, and COSMOS reported increased gastrointestinal bleeding. The authors said safety reporting varied across trials.
Can multivitamins interact with warfarin?
The review authors noted that vitamin K in a multivitamin 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
