Daily multivitamin-mineral supplementation for two years reduces cognitive aging by approximately two years in adults aged 60 and older, as measured by improvements in global cognition and episodic memory across multiple independent cognitive assessments.

Study: Effect of multivitamin-mineral supplementation versus placebo on cognitive function: Results from the clinic sub-cohort of the COSMOS randomized clinical trial and meta-analysis of three cognitive studies within COSMOS.

Taking a daily multivitamin for two years helped older adults think a little better, especially with memory, and the improvement was about as much as what you'd normally see from being two years younger in terms of brain function.

Study: Effects of cocoa extract and a multivitamin on cognitive function: a randomized clinical trial

Taking a daily multivitamin for a few years helped older adults think and remember slightly better — like their brains were almost two years younger. The study found this effect was real and not just by chance.

Study: Impact of Multivitamin-Mineral and Cocoa Extract on Incidence of Mild Cognitive Impairment and Dementia: Results from the Cocoa Supplement and Multivitamin Outcomes Study for the Mind COSMOS-Mind

Taking a daily multivitamin didn't stop older adults from developing memory problems, but those who took it and still had memory issues declined much slower—like their brains aged two years less over the same time.

Study: Effect of multivitamin‐mineral supplementation on change in cognitive function in the COSMOS Clinical subcohort and meta‐analysis of COSMOS cognition studies

Taking a daily multivitamin for two years helped older adults remember things a little better, and their overall thinking may have improved too. This suggests their brains aged a bit slower, though not necessarily by exactly two years as claimed.