Multivitamins and Memory: What the COSMOS Trials Found

By Dr. Ryan Kneessi, ND

Many people take a daily multivitamin with a vague sense that it is good insurance, and many others skip it because they have heard that multivitamins do not do much. For years, the honest answer to whether a multivitamin helps the aging brain was that we simply did not have good long-term trials to say one way or the other. That has started to change, and I think the newer research is worth understanding in some detail, including what it shows and what it does not.

In this article, I want to explain where these findings come from, walk through three free, peer-reviewed studies from the same large trial, and share how I think about them as a functional medicine doctor.

What the COSMOS trial is

COSMOS stands for the COcoa Supplement and Multivitamin Outcomes Study. It is a large randomized trial that enrolled 21,442 adults in the United States, all aged 60 or older, and it tested two things at once. Participants were randomly assigned to take cocoa extract or a placebo, and separately to take a standard daily multivitamin-mineral supplement or a placebo. Because of this design, researchers could look at the effect of the multivitamin on its own while accounting for the cocoa extract.

The main trial was built to look at heart and cancer outcomes, but several smaller studies within it were designed specifically to measure thinking and memory over time. Each one tested cognition in a different way, which is part of what makes the combined results interesting. The participants and the researchers did not know who was taking the real supplement, and the multivitamin used was an ordinary, widely available formula rather than a specialized product.

COSMOS-Mind: cognition tested by telephone

The first of these studies, published in 2023 in Alzheimer’s & Dementia, followed 2,262 participants with an average age of 73 for three years. Every year, trained staff gave them a set of thinking and memory tests over the phone, including word list and story recall, verbal fluency, and number span tasks. The main outcome was a combined global cognition score built from all of those tests.

Cocoa extract did not change global cognition in this study. The daily multivitamin did. People taking the multivitamin had a statistically significant improvement in their global cognition score compared with placebo, and the researchers also saw benefits in memory and executive function, which covers skills like planning and mental flexibility. The effect looked larger in people who had a history of cardiovascular disease, although that subgroup was small. Using the way scores declined with age in their own data, the authors estimated that three years of multivitamin use corresponded to slowing cognitive aging by about 1.8 years, while being careful to describe that comparison as an imprecise yardstick.

COSMOS-Web: memory tested online

The second study, published in 2023 in the American Journal of Clinical Nutrition, took a different approach. It included 3,562 older adults who completed an internet-based battery of thinking tests at home each year for three years. The main outcome was immediate recall on a word list test, which is a common way to measure episodic memory, the kind of memory you use to recall what you heard or did recently.

After one year, the multivitamin group had significantly better immediate recall than the placebo group, and that advantage held on average across all three years of follow-up. The multivitamin did not change the other tests in the battery, such as object recognition and executive function. The researchers estimated that the memory benefit was equivalent to about 3.1 years of age-related memory change. They also noted an important limitation: participants needed a computer, internet access, and some comfort with technology, and the group was more highly educated and less diverse than the general population, so the results may not apply equally to everyone.

COSMOS-Clinic and the combined analysis

The third study, published in 2024 in the American Journal of Clinical Nutrition, is in some ways the most rigorous. It followed 573 participants who came into a research clinic for detailed, in-person neuropsychological testing over two years. In this group, the multivitamin produced a significantly more favorable change in episodic memory than placebo. The change in global cognition leaned in the same direction but fell just short of statistical significance, and there was no clear effect on executive function or attention.

The same paper then pooled the results from all three studies, using only participants who did not overlap between them, for a total of more than 5,000 people. In that combined analysis, the daily multivitamin had a clear benefit on both global cognition and episodic memory compared with placebo. The authors estimated that the effect on global cognition was roughly equivalent to two years less cognitive aging.

How to read these results

I find these studies encouraging, and I also think they deserve a careful reading. The differences between groups were modest when measured in standard units, which means that most individuals would not notice a dramatic change in their day-to-day memory. The comparisons to years of cognitive aging are helpful for putting the numbers in context, but the researchers themselves describe them as rough estimates. The studies also measured test scores, not long-term outcomes like dementia, and they were done in older adults who were mostly well educated and mostly White.

What stands out to me is the consistency. Three groups of people were tested by telephone, online, and in person, and all three pointed in the same favorable direction for memory. Large, long, placebo-controlled trials like these are uncommon in nutrition research, and they move the conversation beyond the idea that a basic multivitamin cannot make any measurable difference.

Why nutrient status may matter for the aging brain

The brain is a demanding organ. It relies on a steady supply of B vitamins, vitamin D, magnesium, zinc, and other micronutrients to support energy production, nerve signaling, and the methylation reactions that help keep homocysteine in a healthy range. As we age, appetite often decreases, absorption of nutrients such as vitamin B12 becomes less efficient, and many people take medications that affect nutrient levels. A small gap in several nutrients at once may be easy to miss, and that is one plausible reason a broad, low-dose supplement could show a benefit across a large group.

The COSMOS researchers did not identify which nutrients were responsible, and the studies were not designed to answer that question. This is where I think testing has real value. Markers such as vitamin D (25-OH), B12, folate, and homocysteine can show whether a person’s needs are being met, and the Omega-3 Index adds another useful piece of the picture for brain and heart health.

How I think about this as a functional medicine doctor

I see a multivitamin as a foundation rather than a solution. Food quality, sleep, physical activity, social connection, and blood sugar balance all have strong research behind them for brain health, and I talk about several of these in my article on brain health and cognitive aging. A supplement does not replace any of those habits. What these trials suggest is that, for many older adults, covering basic micronutrient needs every day may add a modest benefit on top of them.

I also think the type of multivitamin matters for each individual. Some people do better with methylated forms of folate and B12, some need more of a particular nutrient based on their labs, and some are already getting plenty from food and other supplements. If you are wondering whether you need one at all, my article on whether you need a multivitamin walks through the questions I consider, and my guide to methylfolate versus folic acid explains one of the most common differences between formulas. As always, talk with your own clinician before adding a supplement, especially if you take prescription medications.

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This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before making changes to your diet, exercise, supplements, or medications, especially if you are pregnant, nursing, or managing a health condition.