What is the upper limit for magnesium, zinc and iron?

For adults, the tolerable upper intake levels set by the US Institute of Medicine are 350 mg a day of supplemental magnesium — the limit applies to supplements and medicines only, not to magnesium from food — and, counting food as well as supplements, 40 mg of zinc, 45 mg of iron and 2,500 mg of calcium for ages 19 to 50, falling to 2,000 mg from 51. A tolerable upper level is the highest daily intake likely to pose no risk of adverse effects to almost everyone; it is not a target, and it is not the point at which harm begins for a given person. Because most of these levels count food too, a supplement dose at the limit, on top of what you eat, is already over it. The National Institutes of Health’s Office of Dietary Supplements publishes the full tables. Selenium’s limit is 400 micrograms, vitamin D’s 4,000 IU and vitamin C’s 2,000 mg, all counting food; vitamin B6’s is 100 mg in the US, against 12 mg from EFSA, the EU’s food-safety agency, and 10 mg in UK supplement advice; the table runs to a few dozen nutrients.

General information for healthy adults, 18 and over, and not medical advice. It is not for anyone who is under 18, pregnant or breastfeeding, has a medical condition, or takes regular medication; if that is you, a doctor or a registered dietitian should decide what you take. Questions about the app are in the FAQ.

Why do upper limits matter for a training supplement stack?

Because stacks add up quietly. A pre-workout, a “recovery” formula and a sleep blend can each carry a sensible dose of magnesium and together clear the limit before breakfast. Zinc at 50 mg a day or more, for weeks, can lower copper, and the 40 mg limit counts the zinc in food too; iron past 45 mg brings gut symptoms first and worse later, and iron is the one most people should not take at all without a blood test. The limits are the reason to read the labels together rather than one at a time.

How does Liftor cap a stack at the limits?

It carries the table. When the app suggests a supplement plan it clamps every dose to the published upper level — magnesium 350 mg, zinc 40 mg, iron 45 mg, calcium 2,500 mg, selenium 400 mcg, vitamin D 4,000 IU, vitamin C 2,000 mg, and the rest — and it merges the day’s doses across the whole plan before it checks, so two products on the same day cannot sum past the line. Each limit is stored with its source. Those limits count food as well (all but magnesium’s), so a dose at the cap, on top of what you eat, can still pass the total: the cap is a backstop, not a guarantee. The app is still not a doctor; it just refuses to write a dose past a published limit.

What are the upper limits Liftor caps a stack at?

Each is a limit on total daily intake, food and supplements together, except magnesium’s, which counts supplements and medicines only.

Nutrient	Upper limit a day, adults	Note
Magnesium	350 mg	Supplements and medicines only; food is uncapped
Zinc	40 mg	At 50 mg or more, for weeks, can lower copper
Iron	45 mg	Not without a blood test
Calcium	2,500 mg	Ages 19–50; 2,000 mg from 51; 3,000 mg at 9–18
Selenium	400 mcg	Easily reached by two products
Vitamin D	4,000 IU	100 mcg; the common “high-dose” capsules are 5,000 IU
Vitamin C	2,000 mg	Gut symptoms first
Vitamin B6	100 mg (US)	The US limit. EFSA, the EU’s food-safety agency, set 12 mg a day in 2023, after nerve damage was reported from about 50 mg a day; UK public advice is no more than 10 mg a day in supplements

These are the US Institute of Medicine’s tolerable upper intake levels as published by the NIH Office of Dietary Supplements, and they are the table the app carries. Other authorities draw some lines lower, as for vitamin B6 above. The check runs on the day’s total across every product in the plan, not on each product alone, which is the difference that matters when three labels each say “100% of daily value”.

What about caffeine and creatine?

Caffeine has a widely used ceiling and creatine has none, which is a fact about how safe creatine is rather than a gap in the data. The US Food and Drug Administration cites 400 milligrams a day — about two to three 12-ounce cups of coffee — as an amount not generally associated with negative effects in healthy adults; a pre-workout can hold 200–300 of those on its own, so the coffee counts. The International Society of Sports Nutrition’s 2017 position stand on creatine found no evidence of harm at the doses used in sport and recommends 3–5 grams of creatine monohydrate a day as a maintenance dose, with or without a loading week; it is the most-studied supplement in strength training and the one with the clearest effect on it.

Liftor treats both the way the evidence does. Caffeine is counted against the day as a whole when the plan includes it; creatine is written as a plain daily dose in the range above. Neither is required, and the plan says so.

Do you need supplements to get stronger?

No. Every number on this page is a ceiling, not a target, and the two things that decide progress — training that gets harder and food that covers it — are on other pages of this guide. A supplement fills a specific gap: vitamin D in a winter with no sun, iron for a diagnosed deficiency, creatine because it works, magnesium when a diet is short of it. A stack assembled because the labels sounded relevant is mostly a way of paying for expensive urine, and occasionally a way of clearing a limit.

The app suggests supplements when the profile and the food plan leave a gap, not by default, and it caps every suggestion at the limits above. If you take something it did not write, log it, so the day’s total is the day’s total. And if a symptom is the reason you are shopping, a blood test is cheaper than the shelf.

Supplement upper limits: magnesium, zinc, iron