Should You Take a Multivitamin After 40?

Some longevity experts still take one despite optimizing their diets. Are they onto something, or buying nutritional insurance they don't need?

If your diet is good, your workouts are consistent, and you pay attention to your health, a daily multivitamin might seem redundant. Yet some of the people most immersed in nutrition and longevity research still take one.

Harvard physician Howard LeWine is a good example. He had taken a multivitamin for years as inexpensive nutritional insurance, even though he thought his diet was adequate. After a 2024 study found a modest cognitive benefit in older adults, he became more favorable toward recommending one broadly. [1]

That creates a better question than “Do multivitamins work?” Is taking one every day worthwhile when you are already doing most things right?

Start with the disappointing results. Across nine randomized trials involving more than 51,000 people, multivitamins did not demonstrate a reduction in deaths. A separate analysis followed 390,124 generally healthy US adults for more than two decades and likewise found no association with longer life. The second study was observational, so it cannot prove cause and effect, but its results reinforce the randomized evidence. [2] [3]

Heart disease prevention also remains unconvincing. In the 21,442-person COSMOS randomized trial, cardiovascular events occurred at similar rates in the multivitamin and placebo groups. The trial also found no significant reduction in its primary outcome, invasive cancer, over a median 3.6 years. [4]

That does not mean every potential benefit disappeared.

A pooled analysis of four randomized trials found about 7% lower odds of developing cancer, although there was no corresponding demonstrated reduction in cancer deaths. Some trials were more favorable than others, and several years of follow-up may be too short to detect small long-term effects. This is a possible benefit, not a promise of cancer prevention. [2]

The most interesting finding is cognition. In three COSMOS cognitive substudies involving 5,203 older adults, taking a standard daily multivitamin modestly improved global cognition and episodic memory compared with placebo. The pooled change in global cognition was 0.07 standard deviations. Researchers compared that to roughly two years of cognitive aging, but it was a small difference on tests, not proof of two extra years without dementia. [5]

There are meaningful caveats. All three substudies came from the same parent trial, not three independent experiments. An earlier randomized study of 5,947 older male physicians found no cognitive improvement from long-term multivitamin use. And another COSMOS analysis did not find fewer new cases of mild cognitive impairment or dementia over three years, although it had limited power to detect those outcomes. [6] [7]

Then came a March 2026 COSMOS analysis. A daily multivitamin modestly improved two of five DNA-based biological-aging measurements. Interesting, yes. But a younger-looking biomarker is not the same thing as living longer or staying healthier. [8]

The age distinction matters: COSMOS recruited women 65 and older and men 60 and older. Much of its cognitive evidence comes from people around 70. We cannot simply assign those results to a healthy 42-year-old. [4] [5]

For most healthy adults, a basic once-daily multivitamin supplying roughly recommended nutrient amounts appears low risk. But “multivitamin” has no single standard formula. One bottle may provide roughly a day's requirements; another may contain large multiples of them. [9]

The main avoidable problem is stacking. Add a high-potency multivitamin to fortified drinks, a B-complex, vitamin D, and other supplements, and you can overshoot on nutrients you never lacked. Excess vitamin A, vitamin B6, zinc, or iron can have consequences, depending on the dose and duration. High-dose beta-carotene is a particular concern for current and former smokers. Vitamin K also requires attention for people taking warfarin. [9]

COSMOS did report more self-reported gastrointestinal bleeding among multivitamin users (hazard ratio 1.17), while several other reported symptoms were less common. These were secondary safety comparisons, not proof of a causal effect, but worth noting. [4]

There is no convincing evidence that a standard multivitamin routinely harms well-nourished adults. The sensible choice is ordinary doses, not the biggest numbers on the label.

Here is the argument that keeps even informed skeptics interested: the downside of a properly chosen multivitamin is usually small, while the upside may not be zero.

A healthy-looking diet is not a guarantee of perfect micronutrient intake. Food choices vary, absorption changes, and a person can fall short without having a diagnosed deficiency. After 50, for example, some people absorb vitamin B12 from food less efficiently, which is why guidance favors getting adequate B12 through fortified foods or supplements. That does not mean everyone over 50 needs a multivitamin; a targeted B12 source may solve that specific problem. [9]

Think of the daily multivitamin as a backup, not a performance enhancer. The case gets stronger when meals are repetitive, appetite is lower, calories are restricted, or food groups are excluded. It gets weaker when intake is consistently varied and nutrient needs are already covered.

There is also an opportunity cost. A multivitamin cannot supply the fiber, protein, or overall food pattern missing from a poor diet. For the food-quality foundation, see Edition #004 on ultra-processed foods. For the bigger proven levers on cardiovascular health, see Edition #023 on lifestyle.

The practical comparison is not multivitamin versus perfection. It is a modest daily supplement versus doing nothing about plausible nutritional gaps, or addressing those gaps more precisely.

Which nutrient drove the COSMOS cognitive change? We do not know. The study tested a combination, so the result might reflect unnoticed shortfalls, nutrients acting together, or something else. That uncertainty argues against recommending multivitamins universally, but also against declaring them useless based on mortality trials.

A basic multivitamin can be reasonable nutritional insurance, particularly when dietary coverage is uncertain or in older adulthood. That is a conditional Signal. It is not evidence that everyone should start at 40, nor proof of longer life, heart-disease prevention, or dementia prevention.

For a well-nourished adult in their 40s or 50s, skipping one remains reasonable. The modest cognitive signal comes mainly from studies in older adults.

CHECK: Look at your usual week of eating, not your best day. Are you regularly missing food groups, restricting calories, or relying on a narrow menu? Consider individual risk factors for poor absorption too.

CHOOSE: If you want a backup, use a basic, age-appropriate, once-daily multivitamin with most nutrients around 100% of Daily Value, not a megadose formula. The Daily Value is a label reference, not a proven optimal supplement dose. A 50+ formula often contains little or no iron unless there is a reason to include it. [9]

AVOID STACKING: Check other supplements and fortified products first. If you smoke, have a relevant medical condition, or take medications such as warfarin, review the formula with your clinician or pharmacist. [9]

KEEP PRIORITIES STRAIGHT: Correct known deficiencies specifically. Protect diet quality, exercise, sleep, and other higher-impact habits first. If you already eat well and prefer not to take a multivitamin, current evidence gives you no compelling reason to start.

The minimum effective dose is nutritional coverage without unnecessary excess, not an ever-larger supplement stack.

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1. LeWine HE. Should I take a daily multivitamin? Harvard Health Publishing. 2024. https://www.health.harvard.edu/healthy-aging-and-longevity/should-i-take-a-daily-multivitamin

2. US Preventive Services Task Force. Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer: Recommendation Statement. JAMA. 2022. https://jamanetwork.com/journals/jama/fullarticle/2793446

3. Loftfield E, et al. Multivitamin Use and Mortality Risk in 3 Prospective US Cohorts. JAMA Network Open. 2024. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2820369

4. Sesso HD, et al. Multivitamins in the Prevention of Cancer and Cardiovascular Disease: The COSMOS Randomized Clinical Trial. Am J Clin Nutr. 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC9170475/

5. Vyas CM, et al. Effect of Multivitamin-Mineral Supplementation Versus Placebo on Cognitive Function: COSMOS-Clinic and Meta-analysis. Am J Clin Nutr. 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC11103094/

6. Grodstein F, et al. Long-term Multivitamin Supplementation and Cognitive Function in Men: A Randomized Trial. Ann Intern Med. 2013. https://pmc.ncbi.nlm.nih.gov/articles/PMC3858850/

7. Sachs BC, et al. Impact of Multivitamin-Mineral and Cocoa Extract on Incidence of Mild Cognitive Impairment and Dementia: COSMOS-Mind. Alzheimers Dement. 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC10562510/

8. Li S, et al. Effects of Daily Multivitamin-Multimineral and Cocoa Extract Supplementation on Epigenetic Aging Clocks in COSMOS. Nat Med. 2026. https://www.nature.com/articles/s41591-026-04239-3

9. NIH Office of Dietary Supplements. Multivitamin/mineral Supplements: Health Professional Fact Sheet. https://ods.od.nih.gov/factsheets/MVMS-HealthProfessional/

Evidence disclosure: COSMOS received infrastructure and study-product support from Mars Edge and Pfizer Consumer Healthcare (now Haleon), alongside public funding. Some investigators reported other supplement-industry relationships. FOXO Technologies supported the epigenetic analysis with grants and in-kind DNA-methylation data processing; one coauthor was a former employee. Study authors report that product sponsors did not direct trial design or analysis. The findings deserve consideration, with extra caution around small effects.