TL;DR
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A scoping review of clinical trials found that multivitamins most consistently increased blood levels of folate and vitamins B6 and B12. Reports of benefits for pregnancy outcomes and cognitive tests were mixed, and the review did not assess study bias or evidence certainty, limiting conclusions about whether supplements improve health.
A review of 157 publications on multivitamin trials found that supplements most consistently raised blood levels of folate and vitamins B6 and B12, but reported health benefits varied across populations and outcomes. Published in the Journal of Dietary Supplements, the review does not establish that multivitamins generally improve health: its authors did not assess study bias or certainty of evidence, or combine results in a meta-analysis.
The researchers searched PubMed, Scopus and the Cochrane Library for English-language studies through September 9, 2026. Eligible trials generally enrolled adults, lasted at least two weeks and tested oral tablets or capsules containing at least 14 vitamins and minerals. Prenatal studies in low- and middle-income countries could include participants younger than 18. The review included 103 primary intervention reports and 54 related publications; some publications drew on the same trial populations.
Blood-test results most consistently showed increases in vitamin B6, vitamin B12 and folate. Changes in mineral levels were less consistent, with iron, zinc and iodine results varying by circumstances. Responses also differed according to participants’ starting nutrient levels, the product used and the clinical setting. The review said that raising a nutrient level did not consistently lead to a better clinical outcome.
Some individual studies reported pregnancy-related or cognitive benefits, but findings differed across groups and endpoints. 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 are results from specific studies, not evidence that all multivitamins produce the same effects.
Safety findings also varied. Some participants reported mild digestive complaints, particularly with products containing iron or zinc. The review reported modest increases in rash and nosebleeds in the Physicians’ Health Study II, and increased gastrointestinal bleeding in the COSMOS study. It also noted adverse changes in some cataract-trial lens-opacity subtypes. Safety reporting was inconsistent across studies, making it difficult to compare risks.
Nutrient Gains Do Not Guarantee Health Benefits
The review highlights a distinction that matters to people taking supplements: a higher blood concentration of a vitamin is not the same as proof of improved health, longer life or prevention of disease. Clinical outcomes differed by population, product and study, so the findings do not support a single conclusion for every multivitamin user.
About one-third of U.S. adults take multivitamins, according to the source report, and use increases with age. For readers, the evidence offers some reassurance that certain nutrient levels can rise, while leaving the size and reliability of wider benefits uncertain. Product formulas and individual nutritional needs also differ, limiting the usefulness of treating multivitamins as one uniform intervention.
The safety findings are relevant too. The review described generally good tolerability in groups including pregnant participants, older adults and people recovering from surgery, but also reported specific adverse events and uneven safety monitoring. Vitamin K can interact with anticoagulants such as warfarin; people taking these medicines should consult a health professional before using a multivitamin.
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How Researchers Defined the Evidence
This was a scoping review, designed to map a broad body of research rather than calculate one overall effect. The researchers identified 5,263 records, removed 1,537 duplicates and screened titles, abstracts and full texts. They selected 153 articles, then added four through citation searching, for a total of 157 publications.
To qualify, products had to include at least two vitamins and two minerals, with at least 50% of the relevant life-stage Recommended Dietary Allowance or Adequate Intake for 14 or more nutrients. No nutrient could exceed its applicable upper intake limit per daily serving. The review excluded products such as fortified foods, powders, syrups and enteral nutrition, so its findings do not cover every supplement format or product on the market.
Most included studies took place in North America, Europe and Asia. The authors noted that formulas can differ by market and manufacturing period, while people’s needs vary by life stage and health profile. Those differences complicate attempts to apply results from a particular trial to all users.
“Improved nutrient levels did not consistently translate into better clinical outcomes.”
— The review authors
Limits on What Trials Can Show
The review did not assess risk of bias or certainty of evidence and did not perform a meta-analysis. It therefore maps reported findings but does not determine how reliable they are overall or provide a pooled estimate of the size of any benefit. The source material does not provide enough detail to establish whether the reported effects would be meaningful in everyday clinical practice.
It also remains unclear how results apply across the many formulations and populations not directly represented in particular trials. Some related publications used the same trial populations, and safety reporting varied. The review’s findings do not settle whether routine multivitamin use prevents chronic disease, improves longevity or benefits people who do not have a nutrient deficiency.
Specific findings need to stay within their study settings. For example, a short trial involving women with preeclampsia tested multivitamins alongside intravenous magnesium sulfate and reported improvements in proteinuria and selected outcomes. It does not establish prevention of preeclampsia or general benefit in uncomplicated pregnancies.
More Targeted Evidence Is Needed
The review does not announce a new clinical trial or a change in supplement guidance. Its findings point to a need for research that reports product composition, participants’ baseline nutrient status, treatment duration and safety outcomes clearly. Trials focused on specific populations and endpoints could help distinguish biochemical changes from effects that matter to patients.
Readers should not treat this review as individualized advice or assume that all multivitamins have the same effects. People considering supplements, particularly those taking medicines such as warfarin, can discuss their circumstances with a qualified health professional. The next step in the evidence is further study; no single health benefit for multivitamins is established by this review.
Key Questions
Do multivitamins raise vitamin levels?
In the reviewed trials, the most consistent increases were in blood levels of folate and vitamins B6 and B12. Results for other vitamins and minerals varied by population, starting nutrient levels and product.
Did the review show that multivitamins improve overall health?
No general health benefit was established. Some studies reported selected pregnancy-related or cognitive outcomes, but results varied, and improved nutrient levels did not consistently lead to better clinical outcomes.
What safety concerns did the review report?
Some trials reported mild digestive complaints, particularly with products containing iron or zinc. The review also described findings including rash, nosebleeds, gastrointestinal bleeding and adverse changes in some cataract-trial lens-opacity subtypes. Safety reporting differed between studies.
Can multivitamins interact with medicines?
The review notes that vitamin K may interfere with anticoagulants such as warfarin. People taking anticoagulants should consult a qualified health professional before using multivitamins.
How strong is the evidence in this review?
The review mapped trial findings but did not assess risk of bias or certainty of evidence and did not conduct a meta-analysis. Those limits mean it cannot provide a definitive estimate of the overall reliability or size of benefits.
Source: news-medical.net
