TL;DR
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A scoping review of clinical-trial evidence found that multivitamins most consistently raised circulating folate, vitamin B6 and vitamin B12. Evidence for improvements in pregnancy outcomes, cognition and other health measures varied, and the review did not assess study bias or evidence certainty or calculate pooled effects.
A review of 157 clinical-trial publications found that multivitamins most consistently raise blood levels of folate, vitamin B6 and vitamin B12, while evidence that those changes improve health outcomes is mixed. The review, published in the Journal of Dietary Supplements, also identified benefits in some pregnancy and cognition measures, but its authors did not assess study bias or certainty of evidence, limiting how firmly the findings can be interpreted.
The researchers searched the Cochrane Library, Scopus and PubMed for English-language studies available through September 9, 2026. They included trials primarily involving adults, with an exception for some prenatal research in low- and middle-income countries. Eligible products were tablets or capsules providing at least half of the life-stage-specific recommended intake or adequate intake for at least 14 vitamins and minerals, while staying within applicable upper intake limits.
From 5,263 records identified, the team removed 1,537 duplicates and selected 153 articles after screening, then added four through citation searches. The final set comprised 103 primary intervention reports and 54 related publications; some publications used participants from the same trials. Results for minerals were less consistent than those for the three vitamins, with effects of iron, zinc and iodine varying by population and circumstances such as baseline nutrient status or surgery.
Some trials reported improvements in pregnancy-related outcomes or cognitive test performance, but findings differed by group 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 lower 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 do not establish a general benefit for all pregnant people or all multivitamin products.
Nutrient Gains Do Not Settle Health Benefits
The findings matter because multivitamins are widely used: the report says about one-third of U.S. adults take them, with use rising with age. A higher blood level of a vitamin is a measurable biological change, but it does not by itself show that a person will live longer, avoid disease or feel better. The review found that the link between nutrient changes and clinical outcomes was not consistent.
That distinction is relevant to people choosing supplements for a specific goal. The trial results do not support treating all multivitamins as interchangeable: formulations, doses, populations and study durations differed. Some benefits were reported in particular clinical settings, but they cannot automatically be applied to people with different nutritional needs or health conditions. The review is a map of the available trial evidence, not proof that a broad-spectrum supplement improves health for every user.
The safety findings also call for attention to product and patient differences. Most reported use was well tolerated in pregnancy, older participants and after surgery, but some products caused mild digestive symptoms, especially those with iron or zinc. The source review also describes particular adverse-event signals in individual trials. These do not establish that every multivitamin carries the same risk, but they make medication use and product composition relevant to any decision.
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How the Review Assessed Trial Evidence
The review used a broad search and eligibility criteria focused on oral multivitamin products containing at least two vitamins and two minerals. It excluded, among other things, fortified foods, powders, syrups, sprinkles, non-oral preparations and enteral nutrition. This means its findings apply to the defined tablet and capsule products, not every form of nutritional supplementation.
The authors used Joanna Briggs Institute methodology, with two reviewers screening records independently and one checking data extracted by another. However, they did not assess risk of bias or certainty of evidence and did not conduct a meta-analysis. The review therefore describes patterns across studies rather than producing a pooled estimate of how much multivitamins help or harm.
Some additional findings illustrate why individual trial results need careful reading. In a two-week study of women with preeclampsia, adding multivitamins to intravenous magnesium sulfate was associated with improvements in proteinuria and selected maternal and neonatal outcomes. That study does not show that multivitamins prevent preeclampsia or provide the same effects in uncomplicated pregnancies. In the CALERIE study, both randomized groups received multivitamins, so it could not establish the supplements’ independent effect on persistent anemia.
“Improvements in circulating folate, vitamin B6, and vitamin B12 were most consistent.”
— The review authors, as summarized by News-Medical
Limits and Risks Remain Product-Specific
The review does not establish the size or reliability of the reported benefits because it did not evaluate risk of bias or evidence certainty and did not pool results statistically. Trial products, participants, follow-up periods and measured outcomes varied, and some related publications drew on the same trial populations. It is also unclear from the review whether the results apply to products sold in every market or to formulations that have changed over time.
Safety reporting differed between studies. The report notes mild digestive complaints, particularly with iron- or zinc-containing products; modest increases in rash and nosebleeds in the Physicians’ Health Study II; and increased gastrointestinal bleeding in COSMOS. A cataract trial reported adverse changes in some lens-opacity subtypes. These are findings from specific trials, not evidence that all multivitamins cause those effects. The review also warns that vitamin K can interfere with anticoagulants such as warfarin; people taking these medicines should consult a healthcare professional before using a multivitamin.
More Targeted Trials Are Needed
The review itself does not announce a follow-up study or a policy change. Its findings point to the need for better-targeted research that distinguishes products, starting nutrient levels, life stages and clinical outcomes. Trials that report adverse events consistently and assess study quality could help clarify when biochemical changes translate into meaningful benefits and for whom.
For now, the review supports a limited conclusion: multivitamins can raise certain circulating vitamin levels, while broader health effects remain variable and uncertain. A person considering a supplement for a medical condition, during pregnancy or while taking medication should discuss the choice with a qualified healthcare professional rather than infer a personal benefit from results in a different trial population.
Key Questions
Which nutrient levels rose most consistently?
The review found the most consistent increases in circulating folate, vitamin B6 and vitamin B12. Findings for other vitamins and minerals varied across studies and populations.
Does the review show that multivitamins improve overall health?
No. It reports some positive results in selected pregnancy and cognition outcomes, but improvements in nutrient levels did not consistently translate into better clinical outcomes. The review also did not assess evidence certainty or pool results.
Were multivitamins shown to be safe?
Many studies described them as well tolerated in the groups examined, but some reported digestive complaints and other adverse-event signals. Safety reporting varied, so the review does not establish a single risk profile for every product or user.
Should people taking warfarin check before using a multivitamin?
Yes. The review notes that vitamin K may interfere with warfarin and advises people taking anticoagulants to consult a healthcare professional before using multivitamins.
Source: news-medical.net
