It’s the most quotable line in the entire supplement debate: “All you’re doing is making expensive urine.” It shows up in newspaper columns, in doctors’ offices, and in every comment section under any article about multivitamins.
Like most durable one-liners, it survives because it’s partly true. The physiology behind it is real. The conclusion people draw from it is sloppy — and the sloppiness cuts both ways, letting some people dismiss useful supplementation and letting others ignore the doses where the criticism genuinely lands.
The True Part
Vitamins divide into two groups by how they dissolve, and it drives almost everything about how your body handles them.
Water-soluble vitamins — vitamin C and the eight B vitamins — dissolve in body water. Your body holds limited reserves of them, and once blood levels exceed what tissues can take up, the kidneys filter the surplus into urine. Take 1,000 mg of vitamin C when your tissues are already saturated and a large fraction of it will be gone within hours. That’s not a malfunction. It’s the same regulatory system that keeps your blood sodium and water balance in a narrow range.
The most visible demonstration is riboflavin (vitamin B2), which is bright yellow-orange. Take a B-complex and the fluorescent yellow urine an hour later is riboflavin you didn’t need. People find this alarming or funny; it’s neither. It’s just a very visible instance of a process happening constantly with nutrients you can’t see.
Fat-soluble vitamins — A, D, E, and K — behave completely differently. They’re stored in liver and fat tissue and are not readily excreted. Which brings us to the first thing the quip gets wrong.
The Wrong Part, Version One: It Doesn’t Apply to Half of Them
You cannot flush out excess vitamin A, D, E, or K, and you cannot flush out excess iron, selenium, zinc, or copper. These accumulate. That’s precisely why they carry meaningful tolerable upper intake limits and why toxicity is a real (if uncommon) clinical entity for them.
So “you just pee it out” is not merely wrong for these — it’s dangerously reassuring. The nutrients that most warrant caution about overdoing are exactly the ones your kidneys won’t rescue you from. Our guide to supplement upper limits and the explainer on water-soluble vs fat-soluble vitamins lay out where each nutrient sits.
The Wrong Part, Version Two: Excretion Comes After Use
Here’s the logical error at the heart of the phrase. The vitamin appearing in your urine is what was left over after absorption, transport, and tissue uptake — not proof that nothing happened along the way.
If you’re genuinely low on vitamin C, a supplement raises your plasma level, tissues take up what they need, and only the surplus is excreted. The excretion is the tail end of a process that did something. Judging a supplement by what leaves the body is like judging a meal by what’s left on the plate.
The correct version of the criticism is narrower and much more useful: once you’re already replete, additional intake is largely excreted, so extra doses buy you very little. That’s a statement about dose and about who’s taking it — not a blanket dismissal.
Where the Criticism Genuinely Lands: Megadoses
This is the part the supplement industry would rather you skipped.
Vitamin C is the clearest case. Absorption efficiency falls as the dose rises:
- At intakes of roughly 30-180 mg/day, absorption runs around 70-90%.
- Above about 1,000 mg in a single dose, absorption drops below 50%, and the excess is excreted.
- Plasma levels plateau — pushing intake higher stops raising blood concentration proportionally at all.
Which means a 1,000 mg tablet does not deliver anything like ten times what a 100 mg tablet does. The adult RDA sits around 75 mg/day for women and 90 mg for men (higher for smokers), and the tolerable upper limit is 2,000 mg/day, above which GI upset and diarrhea become common. Details in the vitamin C explainer.
B vitamins show a similar saturation pattern. The doses in “high potency” B-complex products — often several thousand percent of daily value — are far past what tissues can use. Two exceptions worth naming: vitamin B6 has a real upper limit (chronic high supplemental intake, generally well above 100 mg/day sustained, has been linked to nerve damage), and B12 absorption is limited by intrinsic factor at any single dose, which is why high-dose B12 products rely on a small percentage of passive absorption rather than on the headline number.
If you want the practical takeaway from all of this: splitting doses beats megadosing. 250 mg of vitamin C twice a day is absorbed considerably better than 1,000 mg once. Our supplement timing guide covers when splitting is worth the trouble.
The Actually Expensive Urine
The real waste isn’t the fraction of a dose you excrete. It’s more mundane:
- Supplementing a nutrient you’re not short on. Correcting a deficiency has measurable benefits; topping up an already-adequate level generally doesn’t. Without a blood test or a clear dietary gap, you’re guessing.
- Paying premium prices for doses past the saturation point. The 5,000% DV product costs more than the 100% DV product and does not deliver 50 times the benefit.
- Proprietary blends that hide how much of anything you’re getting — see how to read supplement labels.
- Products with no meaningful evidence behind them at all, at any dose.
The multivitamin debate is the interesting middle case here. For someone eating a varied diet, a multivitamin’s water-soluble content is largely excreted and its benefit is genuinely hard to demonstrate. For someone with a restricted diet, an absorption issue, higher needs, or a documented shortfall, the same pill can be doing real work. Same product, opposite verdicts — which is exactly why blanket statements about supplements being wasteful are unsatisfying.
Bottom Line
“Expensive urine” describes real physiology and draws the wrong conclusion from it. Excreting surplus water-soluble vitamins is normal kidney regulation, and it happens after your tissues have taken what they need — not instead of it. The criticism does land hard on megadoses, where vitamin C absorption falls below 50% above roughly 1,000 mg, and it doesn’t apply at all to fat-soluble vitamins and minerals, which accumulate rather than flush. The genuinely wasted money is spent on nutrients you weren’t short of in the first place.
This article is for educational purposes only and is not medical advice. Consult a healthcare provider before starting any supplement — especially if you’re pregnant, nursing, taking medication, or managing a health condition.