TL;DR
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A review in the Journal of Dietary Supplements found that multivitamins most consistently increased blood levels of folate and vitamins B6 and B12. Findings on pregnancy outcomes, cognition and other health measures varied, and the authors did not assess evidence certainty or conduct a meta-analysis.
A review of 157 reports on multivitamin trials found that supplements most consistently raised blood levels of folate and vitamins B6 and B12, but did not establish that these changes reliably improve health. The findings, published in the Journal of Dietary Supplements, describe varied results across populations and outcomes, with important limits on how confidently benefits can be judged.
The researchers searched the Cochrane Library, Scopus and PubMed for peer-reviewed studies published in English through September 9, 2026. The review included 103 primary intervention reports and 54 related publications; some publications drew on the same trial populations. Eligible studies tested oral tablets or capsules containing at least 14 vitamins and minerals, with at least half the recommended intake for the relevant life stage, and lasted at least two weeks.
Blood tests showed the most consistent increases in circulating folate, vitamin B6 and vitamin B12. Mineral responses were less consistent: effects involving iron, zinc and iodine varied with circumstances, including participants’ baseline nutrient status and clinical setting. The review also found that improved nutrient measurements did not consistently correspond to better clinical outcomes.
Some trials reported benefits for pregnancy-related outcomes or cognitive test performance, but results differed by population and measure. In the JiVitA-3 trial, multiple micronutrients were associated with lower rates of low birth weight and preterm birth than 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 particular trials, not proof that multivitamins improve outcomes across all pregnancies or populations.
Nutrient Gains Do Not Settle Health Effects
About one-third of U.S. adults take multivitamins, according to the review, and use rises with age. The findings matter because a measurable increase in a nutrient’s blood level is not the same as evidence that a supplement prevents illness, preserves memory or extends life. Readers cannot assume that results for one formulation or group apply to another.
The review points to a distinction between biochemical changes and clinical benefit. A supplement may raise nutrient levels while leaving a particular health outcome unchanged, and effects may depend on an individual’s needs and the product’s ingredients. The evidence therefore does not support a single broad conclusion that multivitamins either improve health generally or provide no benefit.
Safety findings also varied. Trials reported generally good tolerability in some groups, including pregnant participants, older adults and people after surgery, but some products caused mild digestive complaints, particularly when they contained iron or zinc. Individual medicines and health circumstances can affect whether a product is suitable.
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How the Trial Review Was Built
The review used a broad definition of multivitamins: oral products containing at least 14 vitamins and minerals, including at least two of each, with no nutrient above its applicable upper intake limit per daily serving. It excluded products such as fortified foods, powders, syrups and enteral nutrition. Most included studies took place in North America, Europe and Asia; prenatal research in low- and middle-income countries could include participants younger than 18.
The authors used two reviewers to screen records independently and applied Joanna Briggs Institute methods. However, they did not assess risk of bias or certainty of evidence and did not combine results in a meta-analysis. That means the review maps the kinds of findings reported but does not provide a pooled estimate of how large or dependable the effects are.
Products and study populations varied, as did the duration of supplementation and the outcomes measured. The authors said differences in formulations, markets, manufacturing periods and life stages make it difficult to weigh benefits and risks as though all multivitamins were interchangeable.
“Improvements in circulating folate, vitamin B6, and vitamin B12 were most consistent.”
— The review authors, as summarized by News-Medical
Limits on the Health Conclusions
The review does not establish the size or reliability of any overall health benefit because it did not rate study bias or evidence certainty and did not conduct a meta-analysis. Its findings include reports from studies that may share participants, so the 157 publications do not represent 157 entirely separate trial populations.
It is also unclear which formulations, doses and participant groups may benefit most. Outcomes varied across trials, and results from selected pregnancy or cognition studies cannot be generalized to all users. Safety reporting differed between studies, leaving some adverse effects harder to compare.
The report also notes a possible interaction between vitamin K and anticoagulants such as warfarin. People taking these medicines should consult a healthcare professional before using multivitamins. The review does not determine what product, if any, is appropriate for an individual.
More Targeted Evidence Is Needed
The review does not announce a new clinical trial or a change to supplement guidance. Its findings instead point to questions for future research: which formulations work for which populations, how long any effects last, and whether changes in nutrient levels lead to meaningful health outcomes. Studies that report adverse effects consistently and account for participants’ starting nutrient levels could help clarify those questions.
For now, the evidence supports a cautious reading: some nutrient levels commonly rise with multivitamin use, while health effects remain mixed and dependent on the setting. Anyone considering a product alongside medication or for a specific health concern can discuss the ingredients and potential interactions with a qualified healthcare professional.
Key Questions
What did the review find most consistently?
It found the most consistent increases in blood levels of folate and vitamins B6 and B12. That finding concerns nutrient measurements and does not by itself show improved health.
Did the review show that multivitamins improve memory or prevent disease?
No general conclusion of that kind was established. Selected trials reported changes in cognitive test performance and pregnancy outcomes, but findings varied by population and outcome. The review did not assess evidence certainty or pool results in a meta-analysis.
Were multivitamins well tolerated in the studies?
Many studies reported good tolerability in groups such as pregnant participants, older adults and people after surgery. Some trials reported mild digestive complaints, and other specific adverse findings were reported. Safety reporting varied across studies.
Can multivitamins interact with medication?
The review notes that vitamin K may interfere with warfarin and other anticoagulant treatment. People taking these medicines should consult a healthcare professional before using a multivitamin.
Source: news-medical.net
