Scientific studies have shown that multivitamins do have an effect on cognitive abilities when aging, which could explain why some older men here think multivitamins have no effect. They're not taking multivitamins, and thus their cognitive abilities have decreased. COSMOS-Mind included about 2,200 people. It found an association between taking a daily multivitamin and improved cognition, which was equivalent to about three years less of cognitive aging. COSMOS-Web included about 3,500 participants. This study also found a cognitive benefit to taking a multivitamin, though it was smaller than the benefit seen in COSMOS-Mind. https://www.health.harvard.edu/preventive-care/do-multivitamins-make-you-healthier Clearly multivitamins do have an effect, but it is limited to cognitive abilities, better physical stamina and a very small reduction in cancer incidence for people who lack nutrients.