An analysis of over 5,000 people suggests multivitamins protect our mental faculties as we age, raising the possibility that daily doses of these supplements could help guard against diseases such as Alzheimer's.

Researchers, led by a team from Mass General Brigham, ran in-person cognitive tests on 573 participants aged over 60 over the course of two years. The volunteers were split into four groups and given different combinations of cocoa extract supplements, multivitamin supplements, and placebos.

When matched against the brainpower tests that were carried out, the supplements were linked to a statistically significant benefit in terms of overall cognitive skills over two years, and an even greater boost in episodic memory.

The data from this in-person study was then combined with a meta-analysis of two earlier studies, covering another 4,630 people over 60, assessed via phone calls and online tests. This further analysis also showed that those who had taken the supplements performed better in cognitive and memory tests.

"Cognitive decline is among the top health concerns for most older adults, and a daily supplement of multivitamins has the potential as an appealing and accessible approach to slow cognitive aging," says psychiatrist Chirag Vyas from Mass General Brigham.

Taking the review of all 5,203 people together, the researchers say that taking multivitamins appeared to slow cognitive aging by the equivalent of two years on average, compared with taking placebos.

While the new study isn't enough to prove direct cause and effect, it's large enough to make the case that certain supplements can offer important health benefits – something previous research hasn't really demonstrated.

The authors note there was low ethnic and racial diversity among the mainly Non-Hispanic White participants, and they only studied one multivitamin supplement, so their results may not be generalizable. The participants were all over 60, so more research is needed to investigate any benefit to other groups.

A benefit of the analysis is that different methods for assessing cognitive ability were used across the three studies, and yet they all came to the same broad conclusion – that these supplements could be slowing down brain decline.

"The meta-analysis of three separate cognition studies provides strong and consistent evidence that taking a daily multivitamin, containing more than 20 essential micronutrients, helps prevent memory loss and slow down cognitive aging," says Vyas.

With the number of people with neurodegenerative diseases continuing to rise, this is potentially a simple and affordable way of reducing the risk of these conditions developing at an earlier age.

Next, the researchers want to dig deeper into why this relationship between multivitamins and cognitive ability is showing up, because it's not immediately clear which of these multiple vitamins and minerals might be having the most effect on the brain.

"It is now critical to understand the mechanisms by which a daily multivitamin may protect against memory loss and cognitive decline with a focus on nutritional status and other aging-related factors," says epidemiologist Howard Sesso, from Mass General Brigham.

The research has been published in the American Journal of Clinical Nutrition.