Health Reference LibraryCan you take iron and magnesium together?
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
Yes. Unlike calcium, magnesium has not been shown to block iron in human absorption studies, and the NIH iron fact sheet lists calcium, not magnesium, as the mineral that interferes. The worry comes from two places: magnesium containing antacids, which reduce iron absorption because they neutralise stomach acid at gram doses, and the general rule that minerals taken as free ions on an empty stomach can crowd each other. Neither applies to an ordinary magnesium capsule taken with food. If you want a belt and braces routine while correcting a low ferritin, take iron in the morning and magnesium with dinner, which is where magnesium is most useful anyway. Otherwise take them together and move on.
How it works
Iron is taken up in the first part of the small intestine by a transporter that handles free ferrous iron. Calcium interferes with the transfer step and cuts absorption by half at the same meal; manganese and, in water only, zinc compete directly. Magnesium has not shown that behaviour in the isotope studies, and the 2010 review of dietary factors affecting iron absorption does not list it. What magnesium can do is raise the pH of the stomach when it arrives as an antacid in large amounts, and a less acid stomach converts less iron into the absorbable form. Supplement doses of citrate or bisglycinate do not have that effect.
Effective dose
Reference intakes: iron 8.7 mg a day for men and 14.8 mg for women aged 19 to 50; magnesium 300 mg for men and 270 mg for women. There is no dose at which a magnesium supplement has been shown to reduce iron absorption in people, so the question is comfort and habit rather than a threshold.
Timing
If you take both, iron in the morning with water or a light meal, tea and coffee an hour clear, calcium supplements two hours clear; magnesium with the evening meal or before bed. That one schedule handles every iron interaction that is real, and keeps magnesium where its calming effect helps.
Safety profile
Do not take iron without a blood test that shows you need it, and keep iron away from children. Magnesium above 400 mg a day from supplements loosens the bowel; kidney problems mean no magnesium supplements without a GP.
Interactions
Iron: inhibited by calcium, manganese, tea, coffee and phytates, and by zinc at high doses on an empty stomach; helped by vitamin C at the same meal. Magnesium: weakly reduced by very large calcium doses; otherwise free of mineral clashes.
Guideline positions
NIH Office of Dietary Supplements: iron fact sheet, interactions section. Review of iron bioavailability and dietary factors (2010). NHS reference intakes for iron and magnesium. NICE Clinical Knowledge Summary: anaemia, iron deficiency.
Practical framework
Morning iron, evening magnesium, or both together with a meal if that is easier to keep up. Nutri Tailor stocks [iron bisglycinate with vitamin C](/products/iron-vitamin-c), 15 mg of iron per capsule, gentle enough for the morning, and [magnesium bisglycinate](/products/magnesium-bisglycinate), 133 mg of magnesium per capsule, the evening form, both made in the UK. If you are correcting a low ferritin, retest after eight weeks. To read your own result against the UK ranges, use the free blood test result interpreter. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.
Common misconceptions
That magnesium blocks iron the way calcium does: no human study shows it. That the antacid warning applies to magnesium capsules: it is about gram doses that neutralise stomach acid. That you must choose between them: both fit in one day.
Sources
- NIH Office of Dietary Supplements 2025. Iron: Fact Sheet for Health Professionals. National Institutes of Health, Office of Dietary Supplements.
- NIH Office of Dietary Supplements. NIH Office of Dietary Supplements — Magnesium Fact Sheet for Health Professionals. NIH Office of Dietary Supplements (US government).
- National Institute for Health and Care Excellence (NICE, UK government) 2024. Anaemia - iron deficiency: Clinical Knowledge Summary. NICE Clinical Knowledge Summaries.