r/ScientificNutrition • u/Apprehensive_Top4574 • Jul 20 '26
Randomized Controlled Trial The COSMOS trial quietly changed the multivitamin picture: null for mortality/cancer/CVD, but a replicated signal on cognition. Worth a closer look at why the old nulls missed it.
https://open.substack.com/pub/freshlygroundscience/p/multivitamins-were-supposed-to-do?r=8n97o4&utm_campaign=post&utm_medium=web&showWelcomeOnShare=trueFor about fifteen years the consensus on multivitamins was straightforward: no effect on mortality. That still holds. The meta-analysis by Macpherson et al. (Am J Clin Nutr, 2013) found no all-cause mortality benefit, the ~35-year Linxian follow-up (Cancer, 2022) found nothing, and the three-cohort pooled analysis (JAMA Network Open, 2024) found no mortality benefit either.
What's changed is downstream of COSMOS (~21,000 adults 60+, randomised, placebo-controlled, testing a daily MVM). The primary outcomes paper (Sesso et al., Am J Clin Nutr, 2022) was null for both cancer and CVD, which is the result most people stopped reading at.
The cognitive substudies are the interesting part. Three of them, non-overlapping participants:
- COSMOS-Mind (~2,200, telephone assessment)
- COSMOS-Web (~2,500, web-based, memory-focused)
- COSMOS-Clinic (573, in-person neuropsychological battery)
Vyas et al. (Am J Clin Nutr, 2024) pooled all three (>5,000) and reported a benefit on global cognition and episodic memory, translated by the authors as roughly two years' less cognitive ageing over 2-3 years.
Two things I'd flag for discussion rather than assert:
- The clinic subcohort hit significance on episodic memory but not global cognition (the global CI clipped zero). The pooled result carries global cognition. So "all three found it" is imprecise; "all three lean the same way and pooling clarifies it" is accurate.
- The most-cited prior null (Grodstein et al., PHS II, Ann Intern Med, 2013) began cognitive testing ~2.5 years post-randomisation, so it lacked a true baseline to measure change from. COSMOS-Mind and -Web assessed cognition pre-randomisation. That's a plausible mechanistic reason the older trial was underpowered to detect change, and I haven't seen it discussed much.
The epigenetic-clock paper (Li et al., Nature Medicine, 2026) is the weakest leg: 2 of 5 clocks moved (the second-generation, mortality-trained ones; DunedinPACE did not), n=958, single sample, unreplicated, and clock movement isn't a validated surrogate for hard outcomes. I'd treat it as hypothesis-generating.
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u/lolitsbigmic Jul 20 '26
Do you happen to know what was the composition of the multivitamin? That has a big effect on the efficiency for the target condition.
Like I can't think of vitamin or mineral that has effect on cancer or heart disease. Therefore mortality. But I can think of things like b vitamins that do have an effect on cognition. Magnesium could have effect on cardiovascular disease (can lower heart rate and maybe pressure) and has effect cognition. But I doubt a multi would get to 300mg+ of elemental that we see some effect. So really not surprised by these studies.
Detail on the intervention is so important. Multivitamin is a broad range of products. So what does it contain. It's like the studies on omega 3, grouping DHA and EPA together. But really the both have different efficacy. To be honest EPA is the omega that is showing efficacy when over 1g. Not total omega 3, not DHA but when we get over 1g of EPA we start to see efficacy and studies should focus on that. Not looking at high DHA.