Do Multivitamins Actually Work?

The daily multivitamin is one of the most widely taken supplements in the world, largely on the logic of “it can’t hurt, and it might help.” The trial evidence is more specific — and more limited — than that logic assumes.

The largest trial: a real, if narrow, cancer-prevention signal

The Physicians’ Health Study II, published in JAMA in 2012 ^[1], randomised roughly 14,000 male physicians aged 50 and over to a daily multivitamin or placebo and followed them for over a decade. The result: a statistically significant, though modest, reduction in total cancer incidence in the multivitamin group — but no significant effect on cardiovascular disease, and no effect on cancer or cardiovascular mortality specifically.

This is a genuinely well-designed, large trial, and it’s worth taking seriously — but it’s also worth being precise about what it did and didn’t find. It studied one population (older male physicians in the US, already a relatively well-nourished, health-engaged group), it found a cancer incidence effect but not a mortality effect, and it found no cardiovascular benefit at all.

What the broader evidence review concludes

The US Preventive Services Task Force’s 2022 recommendation statement in JAMA ^[2] synthesised the wider trial evidence (including the Physicians’ Health Study II and other large RCTs) specifically on the question of using vitamin, mineral, or multivitamin supplementation to prevent cardiovascular disease or cancer in the general adult population. Its conclusion: the current evidence is insufficient to recommend for or against multivitamin use for this purpose in adults without a known deficiency — not “proven not to work,” but genuinely “not enough consistent evidence either way” at a population level.

”Insufficient evidence” is the honest answer here, not a hedge to avoid picking a side.

Who the evidence more clearly supports

This isn’t a blanket case against multivitamins — it’s a case against treating them as a general insurance policy for an already-adequate diet. The clearer evidence-based cases are:

• Diagnosed or likely deficiency — iron, B12, vitamin D, and similar, ideally confirmed rather than assumed.
• Pregnancy — folate supplementation specifically has strong evidence for reducing neural tube defect risk.
• Restrictive diets — strict vegan diets (B12 in particular), or other diets that structurally exclude major nutrient sources.
• Older adults — reduced absorption of certain nutrients (B12, vitamin D) with age is well documented.

The practical takeaway

For a generally well-nourished adult without a specific deficiency risk, a daily multivitamin is not harmful in the doses typically sold, but the trial evidence doesn’t support it as a meaningful disease-prevention strategy either. It’s a reasonable, low-stakes choice — it just isn’t the insurance policy the marketing implies. This is supplement-adjacent content, so the standard note applies: nothing here is a recommendation to take or avoid a specific product.