In 2007, Sheldon from The Big Bang Theory summed up the mainstream view of multivitamins in two words: expensive urine. The line stuck. It is still the single most repeated argument against taking a multivitamin, and for a long time it was a reasonable summary of the evidence.
That clip is now nearly two decades old. Since then a lot of data has come in, and it has genuinely changed the picture — including a new result reported at a nutrition conference three weeks ago, in people with narrowed arteries.
Here is how the multivitamin story actually changed, what still holds up in the criticism, and what I think is worth paying attention to.
Table of Contents
- What The Official Reviewers Still Say
- The First Crack: A Landmark Eye Study
- The Beta-Carotene Problem
- A Swap That Worked Twice Over
- Why Your Urine Turns Bright Yellow
- When The Wrong Dose Causes Harm
- COSMOS: What Happened To Memory
- The Omega-3 Connection
- The New Result On Heart Function
- What The WHO Guideline Actually Says
- What To Look For In A Multivitamin
- References
What The Official Reviewers Still Say
First, to be fair to the critics: most official reviewers still lean their way. As recently as 2022, the US Preventive Services Task Force — America's independent prevention panel — reviewed multivitamins for preventing heart disease and cancer, and issued an "I" [1].
Insufficient evidence. Not "they work". Not "avoid them". We can't tell.
That grade is worth sitting with, because in the very same review the panel was much more decisive about two specific nutrients. It concluded that the harms of beta-carotene outweigh the benefits, and that there is no net benefit from vitamin E [1]. So the panel was perfectly willing to say "don't" when it thought the evidence supported it. For multivitamins as a category, it said something different: we don't know yet.
That distinction matters for everything that follows, because "we can't tell" is a statement about the state of the evidence — and evidence changes.
The First Crack: A Landmark Eye Study
The first real crack in the "expensive urine" idea came in 2001, with a landmark eye study called AREDS.
People with age-related macular degeneration — the leading cause of blindness in older adults — took a vitamin and mineral formula, or a placebo, a dummy pill. Five years later, the supplement group's risk of moderate vision loss was 19 per cent lower [2].
It proved a principle: the right nutrients, in the right people, can change an outcome that actually matters. Not a blood marker. Not a questionnaire. Vision.
And here is a thought worth holding onto, because I'll come back to it. The eyes are intricately connected to the brain — during development they are literally an outgrowth of it. So if a vitamin and mineral formula can do something for eye health, it's at least reasonable to ask whether it can do something for brain health too.
The Beta-Carotene Problem
But there was a problem sitting inside that original AREDS formula: beta-carotene.
In the 1990s, two large trials gave high-dose beta-carotene to smokers, expecting to prevent lung cancer. Instead, lung cancer went up. The Finnish ATBC trial found an 18 per cent higher incidence of lung cancer in the men who received beta-carotene [3]. The American CARET trial, which combined 30 mg of beta-carotene with retinol, found a lung cancer relative risk of 1.28, and was stopped early [4].
Worth being precise about the doses, because they are often reported as one number: CARET used 30 mg a day, the Finnish trial used 20 mg. Different trials, different doses, same uncomfortable direction of travel.
This is the strongest version of the case against supplements, and it deserves to be taken seriously. A pill designed on the science of its day made things worse for the people taking it.
A Swap That Worked Twice Over
So in the follow-up eye study, AREDS2, researchers compared the original formula containing beta-carotene against an updated version where the beta-carotene was pulled out and replaced with lutein and zeaxanthin — two pigments that concentrate in the retina.
The swap worked twice over.
First, safety. Lung cancer occurred in 2.0 per cent of participants taking the older beta-carotene version, compared with 0.9 per cent on the newer formula — and the cases were mostly in former smokers [5].
Second, the eyes. Compared head to head, the lutein and zeaxanthin formula came out ahead of the original on progression of the disease [6].
This is the crucial point, and it's the one that gets lost when people argue about whether "supplements" work. A well-designed formula locked in a benefit and removed a harm. A formula designed on outdated data caused damage. The only way to tell those two apart is trial data — the benefits have to be shown to outweigh the risks.
So before going any further into the benefits, we need to deal with why so many people are still, rightly, sceptical.
Why Your Urine Turns Bright Yellow
Why does your urine turn bright yellow when you start taking a multivitamin?
It's riboflavin — vitamin B2. It belongs to a family of yellow pigments called flavins, from the Latin word for yellow, and it's absorbed very efficiently from the gut [7].
And the "your body can only absorb so much" criticism? That part is true. There is a ceiling on how much riboflavin you can take up from a single dose, and the recommended daily amount is only 1.3 mg [8].
Yet plenty of multivitamins and B-complex products contain doses orders of magnitude above that. Which is unnecessary, and which is, quite literally, expensive urine. The bright yellow is the proof. It's the dose that matters.
When The Wrong Dose Causes Harm
Sometimes the wrong dose isn't just wasteful. It's harmful. Look no further than vitamin B6.
Australia's medicines regulator has required a warning label on anything supplying more than 10 mg of B6 a day since 2022, after reports of nerve damage — pins and needles, numbness, burning feet. In November 2025 it made its decision final: oral preparations containing more than 50 mg but not more than 200 mg per recommended daily dose become Pharmacist Only Medicines from 1 June 2027, and over a hundred listed complementary medicines will have their registrations cancelled [9].
For context, the recommended daily intake of B6 is 1.7 mg [10]. Plenty of products contain many times that, and switching to a different form of B6 — such as P5P — is not something I'd rely on to avoid the problem.
Here's the trap, in the regulator's own words: the most common symptoms of too much B6 look like the symptoms of too little [9]. So somebody gets tingling feet, reads that a B vitamin might help, and takes more.
I could go on. High-dose vitamin D was associated with more falls and fractures in one trial, not fewer [11]. In the SELECT trial, men taking high-dose vitamin E had a higher rate of prostate cancer than men on placebo [12].
Reaching the recommended intake of a vitamin or mineral is one thing. Megadosing is an entirely different proposition, and it's why doctors like me warn about badly designed supplements. With risks like these attached to the worst products, it's no wonder the whole category gets written off.
COSMOS: What Happened To Memory
Remember the point about the eyes being linked to the brain? This is where it gets interesting.
The COSMOS trial randomised over 21,000 older Americans to a daily, ordinary, off-the-shelf multivitamin or an identical dummy pill, for about three and a half years.
Let's be clear about what it did not do. It did not prevent cancer. It did not prevent heart disease. And people did not live longer.
But inside that trial, three separate groups of researchers ran three cognitive sub-studies, in three different sets of people, each with its own placebo group. Someone then pooled all three — 5,203 people. The conclusion was that a daily multivitamin significantly benefited both global cognition and episodic memory, and supported a role in slowing cognitive decline in older adults [13].
Now, the honest caveat: the clinical effect was small. That's what you'd expect from a roughly two-year sub-study, which in the context of a whole life is very short.
But the point stands. This is a large dataset, randomised and placebo-controlled, showing a cognitive benefit. That is not nothing, and it is not expensive urine.
The Omega-3 Connection
There's a possibility the benefit gets bigger in the right company.
In Oxford, a trial called VITACOG gave older people with mild memory problems high-dose B vitamins for two years and scanned their brains. Researchers then split the participants by how much omega-3 was in their blood at the start.
In those who already had high omega-3 levels, the B vitamins slowed the rate of brain shrinkage by 40 per cent compared with placebo. In those with low omega-3, there was no benefit at all [14].
So the interesting idea was never B vitamins on their own. It's the combination — B vitamins in people who have enough omega-3 on board. That's a lead worth following rather than a finished answer, but it reframes how these nutrients should be studied.
The New Result On Heart Function
Which brings us to the new analysis I mentioned at the start. It also comes from the COSMOS dataset.
16,027 participants filled in a questionnaire every year for three years that scores how much your heart gets in the way of daily life — walking, climbing stairs, dressing, fatigue, breathlessness — graded from zero to one hundred.
The results need to be read carefully. Across the whole group, the multivitamin produced a small but statistically significant improvement in symptom burden — the fatigue and breathlessness side of the score. The physical ability score, which covers things like walking and climbing stairs, showed no effect. The overall summary score improved slightly [15].
But one number in the analysis is much bigger, and it's the only place the researchers used the words "clinically meaningful". In people with carotid stenosis — a narrowing of the artery in the neck — the multivitamin group scored 7.58 points better [15]. That is above the line where a patient can actually feel a difference.
Now the caveats, and they are substantial. That subgroup was 122 people out of more than sixteen thousand. And this is a conference abstract, not yet a peer-reviewed paper. So treat it as a signal that needs proper follow-up, not as a finding you can bank.
What The WHO Guideline Actually Says
Before we get to what to look for, there's one more thing you need to know, because it looks like it flattens everything above.
In July 2026 the World Health Organization published the second edition of its dementia-prevention guideline, and recommended against B vitamins, vitamin E, omega-3 and multivitamins for reducing dementia risk, unless you have a diagnosed deficiency [16].
So I read the full guideline — 168 pages — and searched it for the trial we've spent most of this article on. The word "COSMOS" does not appear anywhere in it.
The guideline explains why, in its own words: the effects of vitamin and/or mineral supplementation were not reassessed as part of this guideline update. Supplements were carved out.
The supplement question got one paragraph, resting on three review papers, none of which covered the COSMOS cognitive results, and concluded that nothing had changed. Which means the 2026 recommendation is, in effect, the 2019 recommendation with a new date on the cover — written before any of the COSMOS memory results existed.
That doesn't make the WHO wrong. It means the guideline is answering an older question than the one people will assume it answered.
What To Look For In A Multivitamin
Here are some general ideas to discuss with your doctor when looking at a multivitamin and mineral. I do have a commercial interest in this area, so please be aware of my potential bias.
No supplement is ever a replacement for a good diet. The foods you eat are critical for your health, and nothing in a capsule changes that.
Beyond that, the things I pay attention to:
- Doses that aren't hundreds or thousands of per cent of the recommended daily intake.
- For eye health, lutein and zeaxanthin — the pair that replaced beta-carotene in AREDS2, and the pair with the trial data behind them.
- I personally don't see a role for vitamin A or vitamin E in a multivitamin, given the safety signals in the trials so far.
- In a perfect world the trace minerals would be chelated — manganese glycinate, for example — so they're absorbed well and are gentle on the stomach.
- Vitamin D that isn't a megadose, plus vitamin K2, boron and magnesium, may work together for bone health. I'm less convinced by K2's data on blood vessel health — we need hard outcome data, meaning rates of heart attacks and strokes, not just imaging.
- Again in a perfect world, the product would be third-party tested. Sites such as labdoor.com test multivitamins independently.
Multivitamins are not magic, and the worst of them genuinely are expensive urine — or worse. But the blanket dismissal has not kept up with the data. The category now has randomised, placebo-controlled evidence behind specific, well-designed formulas. That's a different conversation from the one we were having in 2007.
References
1. https://jamanetwork.com/journals/jama/fullarticle/2793446
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC3485447/
3. https://www.nejm.org/doi/full/10.1056/NEJM199404143301501
4. https://www.nejm.org/doi/10.1056/NEJM199605023341802
5. https://jamanetwork.com/journals/jama/fullarticle/1684847
6. https://jamanetwork.com/journals/jamaophthalmology/fullarticle/1790693
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7010026/
8. https://ods.od.nih.gov/factsheets/Riboflavin-HealthProfessional/
10. https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/
11. https://pubmed.ncbi.nlm.nih.gov/20460620/
12. https://jamanetwork.com/journals/jama/fullarticle/1104493
13. https://pmc.ncbi.nlm.nih.gov/articles/PMC11103094/
14. https://pubmed.ncbi.nlm.nih.gov/25877495/
15. https://nutrition2026.eventscribe.net/index.asp?presTarget=3453489
