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A scoping review of clinical trials found that multivitamins most consistently raised blood levels of folate and vitamins B6 and B12. Evidence for improved health outcomes was mixed, and the researchers did not assess study bias or rate evidence certainty, limiting conclusions about benefits and risks.
A review of 103 primary clinical-trial reports found that multivitamins most consistently increased blood levels of folate and vitamins B6 and B12, but those changes did not reliably translate into better health outcomes. Published in the Journal of Dietary Supplements, the review also found mixed results for pregnancy outcomes and cognitive tests, leaving open whether multivitamins provide broad health benefits for adults.
The researchers searched the Cochrane Library, Scopus and PubMed for English-language studies through September 9, 2026. Eligible products were oral tablets or capsules containing at least 14 vitamins and minerals, with at least half the recommended intake for those nutrients and no daily serving above applicable upper intake limits. Studies had to run for at least two weeks and include more than 10 participants.
The search identified 5,263 records. After screening and citation checks, the review included 157 publications: 103 reports of primary interventions and 54 related publications, some based on the same trial populations. Blood-level results were most consistent for folate and vitamins B6 and B12. Mineral responses, including those involving iron, zinc and iodine, varied by participant and setting; some products also caused mild digestive complaints.
Some selected trials reported pregnancy-related or cognitive benefits, but findings differed by population and outcome. 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 deaths through six months. The SUMMIT trial reported an 18% lower relative risk of early infant mortality. These individual findings do not establish a general benefit for all multivitamin users.
Higher Blood Levels Do Not Settle Health Benefits
The findings separate a measurable biological effect from a demonstrated improvement in health. Raising levels of selected vitamins may matter for people whose nutrient status is low, but the review found that blood-level changes did not consistently predict clinical outcomes. Results also depended on formulation, baseline nutrient status, life stage and clinical circumstances.
That distinction matters because about one-third of U.S. adults take multivitamins, with use increasing with age, according to the source report. The review does not establish that routine use prevents disease, improves memory, or extends life. Nor does it show that all products have the same effects: the products and populations studied varied, making broad conclusions difficult.
Safety findings also require attention. The review describes generally good tolerability in pregnancy, older participants and people recovering from surgery, alongside mild digestive effects in some studies. It also reports specific adverse-event signals in individual trials. These findings are not evidence that every product causes those effects, but they underline why benefits and risks cannot be reduced to vitamin levels alone.
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How Researchers Defined Multivitamins
This was a scoping review, intended to map clinical-trial evidence across formulations and populations rather than calculate one pooled estimate of effect. The review covered a range of adult studies and made an exception for prenatal trials in low- and middle-income countries that included participants younger than 18.
The researchers used Joanna Briggs Institute methodology to screen and extract study information. However, they did not assess risk of bias or certainty of evidence, and they did not conduct a meta-analysis. The findings therefore summarize reported results across studies but do not provide a single estimate of how much multivitamins improve health or how reliable each result is.
Some results came from particular clinical situations, not routine supplementation. For example, a short trial involving women with preeclampsia tested multivitamins alongside intravenous magnesium sulfate and reported improvements in proteinuria and selected outcomes. The report says this does not establish prevention of preeclampsia or benefits in uncomplicated pregnancies.
“Improvements in circulating folate, vitamin B6, and vitamin B12 were most consistent.”
— The review authors, as summarized by News-Medical
Limits on the Evidence and Safety Picture
The review cannot determine the overall size or reliability of multivitamin benefits because it did not rate evidence certainty or assess bias, and it did not pool results statistically. The source material also does not provide full results for every outcome mentioned, including the cognitive findings, so their scale and consistency cannot be established here.
Safety reporting varied among trials. The report notes modest increases in rash and nosebleeds in the Physicians’ Health Study II, increased gastrointestinal bleeding in COSMOS, and adverse changes in some lens-opacity subtypes in a cataract trial. These are findings from specific studies, not proof of a shared effect across all products. Vitamin K can interfere with anticoagulants such as warfarin; people taking those medicines should consult a healthcare professional before using a multivitamin.
It also remains unclear how well the results generalize across products sold in different markets and periods. Formulations, participants’ starting nutrient levels and study durations varied, and some publications drew on the same trial populations.
What Further Trials Need to Establish
The review does not identify a single forthcoming trial or next publication. The immediate next step for interpreting its findings is to distinguish outcomes supported by repeated, well-controlled evidence from results reported in particular populations or individual studies. Longer studies with clearly reported safety data could help address gaps that this review did not resolve.
Future research would also need to compare specific formulations and participant groups, account for baseline nutrient status, and measure clinical outcomes rather than relying only on blood levels. Until then, this review supports a limited conclusion: some nutrient levels rise with multivitamin use, while broad health benefits remain uncertain. Decisions about supplements, particularly alongside medicines such as warfarin, should be discussed with a qualified healthcare professional.
Key Questions
Did the review find that multivitamins improve overall health?
No broad improvement was established. The review found consistent increases in some vitamin levels, but those changes did not consistently translate into better clinical outcomes.
Which nutrient levels rose most consistently?
The most consistent increases were in circulating folate, vitamin B6 and vitamin B12. Results for other vitamins and minerals varied across participants and settings.
Did the review find pregnancy benefits?
Some trials reported benefits for selected pregnancy or infant outcomes, but findings differed. For example, JiVitA-3 reported fewer low-birth-weight and preterm births compared with iron and folic acid, but no significant reduction in infant mortality through six months. Those results do not establish benefits for every pregnancy.
What safety concerns did the review report?
Some products caused mild digestive complaints, especially those containing iron or zinc. Individual trials reported other adverse-event signals, and the review says safety reporting varied. Vitamin K may interfere with warfarin and similar anticoagulant treatment, so users should consult a healthcare professional.
How certain are the review’s conclusions?
There are important limits: the researchers did not assess risk of bias or evidence certainty and did not perform a meta-analysis. The review maps reported findings but cannot establish the magnitude or reliability of overall benefits.
Source: news-medical.net
