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A review of clinical trials found multivitamins most consistently raised blood levels of folate and vitamins B6 and B12. Some studies reported benefits for pregnancy outcomes or cognitive test performance, but improved nutrient levels did not consistently lead to better health outcomes, and the review did not assess evidence quality or pool results.
A review of 157 publications on multivitamin trials found that supplements most consistently raised blood levels of folate and vitamins B6 and B12, but the evidence did not show that those changes reliably improve health. Published in the Journal of Dietary Supplements, the review found varied results across populations and outcomes, leaving the overall clinical benefit uncertain.
The researchers searched the Cochrane Library, Scopus and PubMed for peer-reviewed studies published in English through September 9, 2026. They included 103 primary intervention reports and 54 related publications. Eligible products were oral tablets or capsules containing at least 14 vitamins and minerals, with minimum amounts tied to recommended intake levels; studies had to last at least two weeks and include more than 10 participants.
Blood-test results most consistently showed increases in vitamin B6, vitamin B12 and folate. Mineral changes were less consistent, and responses to iron, zinc and iodine depended on circumstances such as participants’ starting nutrient levels and clinical setting. Some trials reported improvements in pregnancy-related outcomes or cognitive test performance, but those findings varied by study group and outcome. The review said better nutrient levels did not consistently translate into better clinical outcomes.
The review also described mixed safety findings. Multivitamins were generally reported as well tolerated in pregnancy, among older adults and after surgery, although some products containing iron or zinc caused mild digestive symptoms. Individual trials reported other adverse events, including modest increases in rash and nosebleeds in the Physicians’ Health Study II and more gastrointestinal bleeding in COSMOS. Safety reporting differed across studies.
Nutrient Gains Do Not Settle Health Benefits
The distinction between a change in a blood test and a meaningful health improvement matters to people who take multivitamins for prevention or general wellness. The review supports the narrower finding that certain products can raise levels of some vitamins; it does not establish that taking a broad-spectrum supplement prevents disease or improves health for adults as a whole.
Results also differed by formulation, life stage and participants’ initial nutrient status. That makes it difficult to apply a finding from one trial to every product or person. The review’s pregnancy findings, for example, came from particular populations and comparisons rather than demonstrating a general benefit for all pregnancies.
For consumers, the evidence points to a need to distinguish targeted supplementation from broad claims about overall health. The review does not provide a single estimate of benefit or risk for all multivitamins, and it cannot resolve whether a specific product is useful for an individual.
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How the Trial Review Was Built
The review used a broad search across clinical trials, with most included studies conducted in North America, Europe and Asia. It covered different products, populations and durations, which allowed the authors to describe patterns but also meant that findings were not uniform. Some publications drew on the same trial populations.
Among the examples reported, the JiVitA-3 trial found that 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 findings from particular trials and comparisons, not proof that multivitamins produce the same effects in other settings.
In another example, a two-week trial among women with preeclampsia reported improvements in proteinuria and selected maternal and newborn outcomes when multivitamins were added to intravenous magnesium sulfate. The authors’ reported results do not establish that multivitamins prevent preeclampsia or benefit uncomplicated pregnancies.
“The effects varied by supplement formulation, population, and duration of use.”
— The review authors
Limits on the Evidence
The review authors did not assess risk of bias or certainty of evidence, and they did not conduct a meta-analysis. The review therefore does not quantify an overall effect or establish how reliable the reported benefits are. Its scope was to map trial findings, not to determine a definitive answer about multivitamins’ effects on health.
It remains unclear which formulations, if any, provide meaningful benefits for particular groups beyond raising nutrient levels, and how those benefits compare with possible harms. Safety reporting varied between studies. The source material also notes that vitamin K can interfere with anticoagulants such as warfarin; people taking such medicines should consult a healthcare professional before using a multivitamin.
What Further Research Must Clarify
The review identifies a need for studies that better account for product formulation, participants’ life stage and baseline nutrient status, and that measure clinical outcomes alongside blood levels. Stronger assessments of study bias and consistent reporting of adverse events would help clarify the reliability and balance of possible benefits and risks.
For now, the review offers a synthesis of trials available through September 2026, not a recommendation that everyone take multivitamins. Any conclusions about a specific person or product require evidence relevant to that person’s circumstances and the product’s formulation.
Key Questions
What did the review find most consistently?
Trials most consistently found increased circulating levels of folate and vitamins B6 and B12 among people taking multivitamins.
Did the review show that multivitamins improve overall health?
No. Some trials reported benefits for selected pregnancy outcomes or cognitive test performance, but findings varied, and higher nutrient levels did not consistently lead to better clinical outcomes.
Were multivitamins generally well tolerated in the studies?
The review described them as generally well tolerated in pregnancy, among older participants and after surgery. Some products caused mild digestive symptoms, and individual trials reported other adverse events. Safety reporting varied.
What are the main limits of this review?
The researchers did not assess risk of bias or certainty of evidence and did not perform a meta-analysis. Differences among products, populations and study outcomes also limit broad conclusions.
Should people taking warfarin ask before using a multivitamin?
The source report says vitamin K may interfere with anticoagulants such as warfarin. People taking these medicines should consult a healthcare professional before using multivitamins.
Source: news-medical.net
