Should You Take a Multivitamin? What the Science Actually Says

Marcia Howard
Oct 15
4 min read

The problem: nutrient gaps are common (on both sides of the pond)

Food first, yes. But “perfect diet, every day” is… not a thing. Recent national surveys show meaningful gaps:

UK: In 2019–2023, 18% of UK adults (19–64) were vitamin D deficient, jumping to 31% in winter. Intakes of several minerals (magnesium, calcium, iodine, iron) are sub-optimal in specific groups, especially teen girls and many women. GOV.UK +3GOV.UK +3MRC Epidemiology Unit+3
US: Using CDC/IOM cut-offs, about 8% are vitamin D deficient and roughly one quarter at risk of inadequacy; inadequacy is higher in some ethnic groups and in winter. Around 42% fall short on calcium and ~50% miss the magnesium EAR, depending on the dataset and supplements used. ScienceDirect+3CDC+3PMC+3

Why care? Folate deficiency is linked to DNA damage (uracil misincorporation and chromosome breaks), and low magnesium is tied to cellular ageing pathways (telomeres, genomic stability). That’s biochemistry, not clickbait. PubMed+2FASEB Journal+2

“Miracle pill” or “expensive urine”?

Multivitamins (MVMs) are wildly popular, and the hot take is often: “You’re just making your pee pricey.” The truth is more nuanced:

Cognition: In the large COSMOS programme, daily multivitamins improved global cognition and episodic memory versus placebo. A meta-analysis of COSMOS cognitive sub-studies suggested gains roughly equivalent to ~2 years’ younger cognitive performance. That’s meaningful for healthy ageing. American Journal of Clinical Nutrition+2PubMed+2
Longevity: A 2024 analysis pooling ~400,000 US adults found no mortality benefit (hazard ratio ~1.04 for daily users). Translation: multivitamins don’t make you live longer, but they don’t shorten life either. JAMA Network+1

What a multivitamin is good for

Think of an MVM as nutritional insurance: it can reliably top up common gaps (vitamin D, magnesium, iodine, etc.) and — per COSMOS — likely supports brain ageing at the margins. It doesn’t replace a whole-food diet, sleep, movement, stress management, or clinical care. (If only!)

UK vs US: practical differences

Vitamin D policy: UK guidance recommends 10 µg (400 IU) daily in autumn/winter (year-round for many). In the US, there’s no blanket supplement policy; clinicians often test and tailor. Either way, deficiency is seasonal and demographic — test if you’re unsure. GOV.UK
Fortification: The US food supply is more heavily fortified (folic acid, etc.) than the UK, which partly explains different deficiency profiles. (Women of child-bearing potential in both regions should follow local folate/folic acid advice.)

How to choose a serious multivitamin (and avoid the duds)

Use third-party testing as your north star. Look for one (or more) of these quality marks on the exact product you’re buying:

USP Verified (potency/purity; prominent in US mass-market). Quality Supplements
NSF Certified for Sport® (athlete-grade contaminant testing; also used by some general multis). NSF Sport
Informed-Sport / Informed-Choice (LGC; common in the UK/EU; batch-tested for banned substances). Informed Sport+1

Trusted examples (UK & US availability noted)

This isn’t an endorsement of everything each brand sells — check the specific product’s certificate page or packaging.

USP Verified (US widely available; some items ship to UK):

Nature Made (multiple multis & single nutrients carry the USP Verified mark). Nature Made®
Kirkland Signature, Member’s Mark, trunature, Natrol, vitafusion, Nature’s Bounty, YouTheory (selected products are USP Verified — verify the exact SKU). Quality Supplements

NSF Certified for Sport® (US/International):

Thorne Basic Nutrients 2/Day (the multi itself is NSF Certified for Sport — ideal when you want athlete-grade screening). Thorne+1
Klean Athlete – Klean Multivitamin (the multi carries NSF Certified for Sport). NSF Sport

Informed-Sport (UK/EU focus; batch-tested):

Healthspan Elite – Gold A–Z Multivitamin (Informed-Sport listed brand/products; check batch). Informed Sport+1
BULK™ – Sports Multi AM:PM (Informed-Sport; lab-tested per batch). Bulk+1
Science in Sport – Advanced Multivitamin (Informed-Sport certified). Informed Sport
6d Sports Nutrition – Multivitamin (Informed-Sport certified; EU/UK availability). Informed Sport

Other third-party-tested options:

Ritual (Clean Label Project certified; third-party lab testing disclosed; transparent supply chain. Not an athlete/banned-substance programme.) Clean Label Project+1

Quick shopping tip: certification status can vary by batch and SKU. Always match the seal on the bottle to the scheme’s public database (USP, NSF, Informed-Sport) before buying. Quality Supplements+2NSF Sport+2

Who likely benefits most?

Low sun exposure / darker skin tones / winter in the UK → vitamin D shortfall risk. A multi with ~10–25 µg (400–1000 IU) vitamin D3 can help, but correct deficiencies with targeted dosing under guidance. GOV.UK
Low-dairy or vegan diets → watch calcium, iodine, B12; choose a multi that actually includes meaningful amounts (or combine with singles). UK vegans often need iodine specifically. GOV.UK
Midlife & beyond → COSMOS suggests a cognitive edge from daily MVMs; choose products with bioavailable B-vitamins (e.g., methyl-folate, methyl cobalamin or adenosyl/hydroxocobalamin). PubMed

Sensible guardrails (because more ≠ better)

Avoid mega doses of vitamin A (retinol) unless prescribed; stick close to RDA levels if pregnant or planning.
Iron in a multi is for those who need it — many adults (esp. men/post-menopause) do not; test ferritin first.
If you’re on medication (thyroid, anticoagulants, retinoids), check interactions.

Bottom line

If your diet is consistently excellent and your bloods are immaculate, you may skip the multi. For most real humans, though, a third-party–tested, sensibly-dosed multivitamin is practical insurance against common gaps — and the best current evidence says it can help keep cognition a touch sharper with age, even if it won’t add years to your life. PubMed+1

Sources (selected)

UK vitamin D status & winter effect: National Diet and Nutrition Survey 2019–2023. GOV.UK +1
UK micronutrient intakes across mid-life (magnesium, calcium, iodine, iron shortfalls in women/young adults): Derbyshire 2018; NDNS time-trend report. PMC+1
US vitamin D status: CDC/NCHS data briefs & NHANES analyses. CDC+1
US calcium & magnesium shortfalls: USDA/ARS and recent NHANES reviews. ARS+1
COSMOS cognition meta-analysis (AJCN 2024). PubMed
Multivitamins & mortality (JAMA Netw Open 2024). JAMA Network+1
Folate & DNA integrity; magnesium & ageing biology. PubMed+2FASEB Journal+2
Third-party testing programmes and certified examples: USP, NSF Certified for Sport, Informed-Sport. Quality Supplements+2NSF Sport+2