A daily multivitamin helps you live a longer, healthier life

What actually happened

This was one of the largest and longest looks at the question ever done: three big prospective cohorts, 390,124 generally healthy adults, over two decades of follow-up, led by researchers at the National Institutes of Health's National Cancer Institute. Earlier studies had given mixed signals partly because they were smaller or shorter; this one had the size and duration to see a mortality effect if one existed.

It did not find one. Daily multivitamin users were no less likely to die over the study period than non-users; the analysis even carefully accounted for the fact that people sometimes start taking vitamins because they have become ill, which can make supplements look falsely harmful. After that adjustment, the verdict was simply no benefit for longevity.

The careful reading is important: this is about healthy adults taking multivitamins for general 'insurance,' not about people with a diagnosed deficiency or a specific medical need, for whom targeted supplementation still matters. But the popular idea that a daily multivitamin extends the lifespan of an already well-nourished person is, on the best current evidence, not supported.