Can a Multivitamin Slow Down Brain Ageing?

Memory or brain: two kinds of “ageing” not to confuse

What does “the brain ages” mean?

Two things, really, that must be separated to answer honestly. On one side, cognitive ageing: the performance of memory, attention, focus and thinking that slowly declines with age – what many simply call memory loss. It is measured with tests – recalling a list of words, chaining together numbers. On the other side, the biological ageing of the brain: the brain tissue that slowly shrinks, year after year. That one is not inferred from a test; you see it, by measuring brain volume on repeated MRI scans over time.

Why does this distinction change everything?

Because a treatment can act on one without touching the other. You can improve a score on a memory test without the brain shrinking any more slowly – and conversely, slow the loss of brain tissue without a spectacular immediate effect on tests. These are two distinct targets. Now, the question “does a multivitamin slow down brain ageing?” blends the two. The honest answer therefore treats each target separately: first memory, where the multivitamin has results; then the brain itself, where the story is very different.

What the COSMOS trial actually showed

What exactly was discovered?

That a daily multivitamin slightly curbs memory decline in older adults. That is the result of the large US research programme COSMOS, run in more than 21’000 adults aged 60 and over. In its online arm, participants taking a multivitamin (the widely sold Centrum Silver) did better on a word-recall test than those on placebo, as early as the first year, with the gain held over three years^[1]. Another arm, run by telephone, found a benefit on global cognition and memory^[2]. By pooling its sub-studies, the team estimated the effect at the equivalent of about two years of cognitive ageing^[3].

Is it an effect you actually feel?

No, and this is a crucial nuance. “Two years of cognitive ageing” is a statistical translation of a weak effect, observed across thousands of people. At an individual level there is nothing spectacular to feel: no one “senses” their memory improving by swallowing a capsule. It is an average signal, useful at population level, not a personal transformation. The authors themselves stay cautious and speak of a “promising” lead, still to be confirmed.

Is the benefit the same for everyone?

Not that either. In the telephone arm, the effect was more pronounced in people with a cardiovascular history^[2] – a group often more exposed to nutritional imbalances. Experts convened in 2025 for a summary on cognitive ageing reached the same idea: the multivitamin is mainly of interest for filling insufficient intakes, common in older adults, rather than as a universal cognitive booster^[10]. We will come back to this below: the starting profile changes everything.

And what about dark chocolate?

Good question, because the COSMOS programme did not test only the multivitamin. Originally, this large clinical trial aimed at the prevention of cardiovascular disease and cancer – among the main chronic diseases – in older adults, and it compared in parallel a cocoa flavanol extract (a cocoa supplement) – the compounds of dark chocolate, studied notably for blood circulation. The verdict: cocoa showed no benefit on cognition^[2]. So it was the pairing of vitamins and minerals, and not the chocolate, that carried the small effect observed on memory.

Through what mechanism does it act? We don’t know yet

This is one of the most honest points to raise: the COSMOS researchers acknowledge that the mechanism remains unknown. The simplest hypothesis is the correction of insufficient intakes of micronutrients. Another lead often put forward involves antioxidants: certain vitamins and minerals, through their antioxidant properties, help neutralise free radicals, those molecules arising from oxidative stress that can cause oxidative damage to brain cells, neurons included. Appealing as it is, this explanation remains unproven for a multivitamin: at this stage we observe an effect without having proven its cause.

The missing link: what about the brain itself?

Does a multivitamin slow the shrinkage of the brain?

To date, no trial has shown it. This is the point most often left unsaid. The multivitamin studies, including COSMOS, measured cognitive tests – not brain volume. They simply never scanned a brain. Saying that a multivitamin “slows down brain ageing” in the biological sense therefore means going beyond the available evidence. The result exists for memory; for brain tissue, it does not.

So what does slow the shrinkage of the brain?

There are indeed trials that managed it – but with a very different product. Researchers in Oxford gave older adults with early memory problems high doses of three B vitamins (folic acid, B6 and B12). Result: in the treated group, the brain shrank markedly more slowly over two years than on placebo^[5]. A follow-up analysis showed that the protection targeted precisely the brain regions most vulnerable to ageing, with a considerable slowing of atrophy^[6]. That is what evidence about the brain itself looks like.

Why these B vitamins, and not a multivitamin?

Because the mechanism is targeted. These B vitamins lower homocysteine, an amino acid in the blood which, in excess, goes hand in hand with faster brain atrophy. And the effect appeared only in people whose homocysteine was high to begin with. A detail that complicates the picture further: the benefit for the brain was clear only if the omega-3 level was also adequate^[7]. This is a long way from a multivitamin “for everyone”: this is a high-dose treatment, for a specific profile, under specific conditions.

Why it works for some and not others

Why does one trial find an effect and another not?

Because everything depends on what was missing to begin with. Long before COSMOS, a large US trial had followed nearly 6’000 physicians aged 65 and over for years: a daily multivitamin brought no cognitive benefit there compared with placebo^[4]. The authors offered a simple explanation: this population was perhaps too well nourished to benefit from a supplement. A multivitamin only “recharges” what is low; where nothing is missing, it adds nothing.

Nutritional status, the real hidden variable

This is the thread running through all the research. The multivitamin mainly helps when an intake is genuinely insufficient – a situation that becomes common with age, as absorption falls and appetite drops. Conversely, in a person who eats a varied diet and has no deficiency, the expected gain is close to zero. This is not a contradiction between the studies: it is the same rule expressing itself according to the audience. The multivitamin acts as a corrector of deficiency, not as a youth pill.

And the other “brain vitamins”?

The same principle comes back everywhere. A large summary of trials concluded that B vitamins can help maintain cognition in older adults, in connection with the lowering of homocysteine – but with variable results^[8]. On the vitamin D side, a large trial found no effect on cognitive decline in the general population, with a possible benefit limited to certain subgroups^[9]. Other nutrients are under study – choline, or the lutein in green vegetables – but without solid evidence to date. No vitamin behaves like a treatment for the brain: their value lies in filling a gap, when one exists.

Multivitamin and dementia: what the trials don’t say

Does a multivitamin prevent Alzheimer’s disease?

Nothing allows us to claim so, and this is a boundary to respect. The multivitamin studies measured performance on tests, not the occurrence of dementia or Alzheimer’s disease. Slightly slowing the decline of a memory score is not the same as preventing a neurodegenerative disease – two very different levels of ambition. No study has shown that a multivitamin reduces the risk of developing dementia.

Why is this caution not just a formality?

Because it is also a legal requirement, and a matter of honesty. In Switzerland as in the European Union, a dietary supplement is a food, not a medicine: it can neither prevent, nor treat, nor cure a disease, and no advertising may suggest it. The slide from “improves a memory test” to “protects against Alzheimer’s disease” is exactly the shortcut that the regulation forbids – and that the science does not support. The good news remains solid: preserving a little of your everyday functions is already useful, without needing to promise the impossible.

Should you take one? The practical and legal frame

Who is a multivitamin really useful for?

For specific profiles, above all after 60. Older adults, whose absorption of B12 and synthesis of vitamin D decline, people with a poorly varied diet, or those whose intake is low: there, a multivitamin plays its role as a safety net on micronutrients, and that fits the modest benefit seen in COSMOS. For a young, healthy person who eats a varied diet, the value is much lower: better to look after the plate first.

What can you honestly expect?

A top-up, not a guarantee. A multivitamin can help fill small nutritional gaps, and several of its nutrients carry authorised health claims – for example “zinc, iron and iodine contribute to normal cognitive function” or “B vitamins contribute to the normal functioning of the nervous system”. These wordings say exactly what they say: support for normal functions, not a treatment, and certainly not a rejuvenation of the brain.

How to choose and use it well?

A few simple markers. Check the actual dose against the nutrient reference values, the form of the nutrients (some, like B12 as methylcobalamin, are well absorbed), the clarity of the labelling and the origin. In Switzerland, supplements are foods under the oversight of the FSVO. Avoid stacking overlapping products and mega-doses: more is not better, and some fat-soluble vitamins can accumulate. If you are on treatment, pregnant or unwell, seek advice from a healthcare professional.

What matters most for a well-ageing brain

Before any capsule, it is habits that matter most for cognitive health – and the research is far more solid on that side. A healthy, balanced diet rich in fruits and vegetables and whole grains, lightly processed (approaches like the MIND diet, designed for brain health, draw on the Mediterranean diet), regular physical exercise, sufficient sleep, mental stimulation, stress management and social connection form the real foundation of a brain that ages gently. A multivitamin replaces none of these pillars: it comes, at best, as support when an intake is missing.

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