Tick the supplements you take. You get which pairs to take at different times, which go well together, which are about the amount rather than the timing — each with the official source quoted — and when to take each one.
Your 4 supplements
1 pair to space apart Take 1 pair at different times: iron + calcium. 2 pairs go well together: iron + vitamin C and calcium + vitamin D. For 3 pairs the sources we read say nothing either way.
This checks how nutrients affect each other’s absorption — not medicines. For anything you take on prescription or from the pharmacy counter, use a drug interaction checker such as the Drugs.com interaction checker, and ask your pharmacist: they can see everything you take.
This is not medical advice and it does not diagnose anything. If you take blood thinners, antidepressants or blood-pressure medication, or have been told you have an iron or kidney condition, talk to your doctor or pharmacist before combining supplements.
Take iron and calcium at different times of the day, and leave 2 hours between iron and coffee, tea or dairy (NHS). Iron of 25 mg or more taken with zinc lowers zinc absorption. Vitamin C with iron, and vitamin D with calcium, go well together. Zinc and magnesium are fine together at supplement doses, and vitamin D with K2 has no official rule either way.
How to use it
Tick what you take. The checker looks at every pair and sorts them: take at different times, good together, about the amount rather than the timing, nothing published against them together — and, for the rest, that the sources say nothing either way. Every rule quotes its source, and under it is when to take each one. It checks how nutrients affect each other’s absorption only; it does not check medicines.
Every rule it uses, and where it comes from
| Pair | What the source says to do | Source |
|---|---|---|
| Iron + calcium | Take at different times | NIH ODS |
| Iron + zinc | Take at different times | NIH ODS |
| Iron + coffee or tea | Take at different times — 2 hours | the NHS |
| Iron + milk, yogurt or cheese | Take at different times — 2 hours | the NHS |
| Iron + vitamin C | Good together | NIH ODS + the NHS |
| Calcium + vitamin D | Good together | NIH ODS |
| Zinc + copper | Watch the amount | NIH ODS |
| Zinc + magnesium | Nothing published against | NIH ODS |
| Magnesium + vitamin D | Nothing published against | NIH ODS |
| Vitamin D + vitamin K (K1 or K2) | Nothing published against | NIH ODS |
| Folic acid + vitamin B12 | Watch the amount | NIH ODS |
A gap in hours appears only where a source prints one: the NHS’s 2 hours around iron. For iron and calcium, NIH ODS says “at different times of the day” and adds that the effect “has not been definitively established” — so the page gives no hour figure it would have to invent.
Worked examples
- Iron, calcium, vitamin D and vitamin C (the page’s example). One pair to space apart — iron and calcium; two that go well together — iron with vitamin C, calcium with vitamin D; and three pairs the sources say nothing about.
- An iron tablet with the morning coffee. The NHS: “Do not take it with tea, coffee, eggs or dairy products”, and leave a 2-hour gap.
- Zinc and magnesium at bedtime. Fine together: the one study NIH ODS cites found interference at 142 mg of zinc a day — more than three times the 40 mg upper limit.
- Vitamin D3 with K2. No official body we read recommends the pair or advises against it; NIH ODS notes they are often sold together. Both need a little fat to absorb — and vitamin K is the one to ask about first if you take a blood thinner.
- Folic acid and B12. Not a timing question: high folic acid “might mask vitamin B12 deficiency”, so a B12 blood test matters more, not less.
Common mistakes
- Taking iron with breakfast coffee or milk. Both cut the iron you absorb; the NHS says leave 2 hours.
- Taking all your calcium at once. “Absorption from supplements is highest with doses of 500 mg or less” — split a larger amount.
- Swallowing vitamin D, E or K on an empty stomach. They need some fat to absorb; take them with a meal.
- Reading “nothing published” as “safe”. It means the official sources say nothing either way — not that anyone has shown the pair is fine.
- Using this for medicines. It is not an interaction checker. A pharmacist, who can see everything you take, is.
Frequently asked questions
What vitamins should not be taken together?
Of the common ones: iron and calcium (take them at different times of the day), iron and zinc when the iron is 25 mg or more, and iron with coffee, tea or dairy (leave 2 hours). Very high zinc also lowers copper — an amount question rather than a timing one.
Can you take vitamin D and K2 together?
Yes — nothing official advises against it, and they are often sold in one capsule. No official body we read recommends the pair either. Take them with a meal that has some fat in it. If you take warfarin or another blood thinner, ask your doctor before taking any vitamin K.
Can you take vitamin D and calcium together?
Yes. NIH ODS: “Vitamin D is required for calcium to be absorbed in the gut by active transport”. Keep each calcium dose at 500 mg or less, and take calcium carbonate with a meal.
Should iron be taken with vitamin C?
It can be: vitamin C “enhances the bioavailability of nonheme iron” (NIH ODS), and the NHS notes a doctor may suggest orange juice or a vitamin C supplement with iron. The exception is hemochromatosis, where the liver specialists’ advice is to avoid iron and vitamin C supplements.
Can you take zinc and magnesium together?
Yes, at supplement doses. The only interference NIH ODS reports is at 142 mg of zinc a day, far above the 40 mg upper limit.
Can I take vitamin D and magnesium together?
Nothing published says to separate them. NIH ODS notes that magnesium affects the active form of vitamin D; take the D with a meal that has some fat.
What is the best time to take vitamins?
Vitamin D, E and K with a meal that has some fat; iron on an empty stomach if you can (with food if it upsets you), away from coffee, tea, dairy and calcium; calcium carbonate with a meal, 500 mg or less at a time. For most others the sources give no timing.
Does this check my medicines?
No, on purpose. Getting a drug interaction wrong can hurt someone, so use a real interaction checker and ask your pharmacist — they can see everything you take.
Read next
- Vitamin compatibility
- Multivitamins for adults: how to choose
- Folic acid for women and men
- What is a nootropic stack?
- Can you take nootropics with antidepressants?
- The Vitamin & Mineral Dose Lookup — the RDA and the upper limit for each one.
This is not medical advice, and nothing here diagnoses or treats anything. It checks nutrients against each other, never medicines: talk to your doctor or pharmacist, especially if you take blood thinners, antidepressants or blood-pressure medication. Some links on this site are affiliate links: I buy what I review at full price, and a commission never changes a verdict.