Health Reference LibraryCan I take calcium 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. At the doses in a normal supplement, calcium and magnesium can be taken together without one blocking the other. The absorption clash people have heard about is calcium and iron, not calcium and magnesium; the 1991 isotope study showed calcium cutting iron absorption by half, and nothing of that size exists for magnesium. The one caution is dose. A single calcium dose above about 500 mg can modestly reduce how much magnesium is absorbed at the same sitting, so if you take large amounts of both, split them across meals. Below that, take them together and stop worrying about ratios.
How it works
Calcium and magnesium share some of the same transport routes in the gut, and at high concentrations they compete for them. In practice the competition only shows at supplement doses well above what most people take. The interaction that is well documented in this mineral family is calcium against non haem iron: in the 1991 study, 165 to 600 mg of calcium reduced iron absorption by 50 to 60 percent. Calcium and magnesium against each other at 200 to 400 mg is not a measurable problem.
Effective dose
UK reference intakes: calcium 700 mg a day, magnesium 300 mg for men and 270 mg for women. Below 500 mg of calcium and up to 400 mg of magnesium at one sitting, take them together. Above that, put the calcium with one meal and the magnesium with another, or take the magnesium in the evening. Someone on 1000 mg or more of calcium a day for bone protection should already be splitting it, and the magnesium fits into the other half of the day.
Timing
No spacing needed at ordinary doses. If you are splitting, calcium with breakfast or lunch and magnesium with dinner works for most people, and it puts the magnesium where its calming effect is useful.
Safety profile
Calcium supplements above 1500 mg a day can cause stomach pain and diarrhoea, and the NHS advises against exceeding that. Magnesium above 400 mg a day from supplements can loosen the bowel. Anyone with kidney problems should not take either without their GP.
Interactions
Calcium reduces iron absorption when taken at the same time; keep calcium supplements two hours away from iron. Calcium and zinc compete a little at high doses, again only with supplements on an empty stomach. Food buffers all of these.
| Interaction | Issue | Guidance | Citation |
|---|---|---|---|
| Calcium or magnesium and iron | Calcium reduces non-haem iron absorption | Separate iron supplements from calcium- or magnesium-containing meals by around 2 hours | NIH ODS — Calcium Fact Sheet; NIH ODS — Iron Fact Sheet |
| Calcium or magnesium and zinc | High single doses of divalent cations compete for absorption | Separate single doses of zinc from calcium or magnesium by around 1-2 hours | NIH ODS — Magnesium Fact Sheet; NIH ODS — Zinc Fact Sheet |
Guideline positions
NHS: calcium 700 mg a day, do not exceed 1500 mg from supplements. NHS: magnesium 300 mg men, 270 mg women; supplements up to 400 mg unlikely to cause harm. Calcium and iron absorption, dose dependent inhibition, isotope study (1991).
Practical framework
Most adults get enough calcium from food and are more likely to be short of magnesium, so check your diet before buying a combined product with a set ratio; the ratio should follow your need, not the label. If you want both in one capsule, Nutri Tailor stocks calcium and magnesium citrate malate, 50 mg of calcium and 51 mg of magnesium per capsule, and for magnesium on its own magnesium bisglycinate at 133 mg per capsule, both made in the UK. Bone density questions belong with your GP. 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 calcium and magnesium must be taken in a 2 to 1 ratio: no trial supports a set ratio. That calcium cancels magnesium: not at ordinary doses. That a cal mag tablet covers both needs: check each mineral against its own reference intake.
Who this matters for
This entry is relevant for the following groups and situations:
- Pregnancy
- Breastfeeding
- Adults over 65
- Post-menopause
- Kidney impairment
Recent updates
Reviewed and corrected against sources on , ,
Sources
- Hallberg L, Brune M, Erlandsson M, Sandberg AS, Rossander-Hultén L 1991. Calcium: effect of different amounts on nonheme- and heme-iron absorption in humans. American Journal of Clinical Nutrition. PMID: 1984335 · DOI: 10.1093/ajcn/53.1.112
- NIH Office of Dietary Supplements. NIH Office of Dietary Supplements — Magnesium Fact Sheet for Health Professionals. NIH Office of Dietary Supplements (US government).
- NIH Office of Dietary Supplements. NIH Office of Dietary Supplements — Calcium Fact Sheet for Health Professionals. NIH Office of Dietary Supplements (US government).
- Mah J, Pitre T 2021. Oral magnesium supplementation for insomnia in older adults: a Systematic Review & Meta-Analysis. BMC Complementary Medicine and Therapies. PMID: 33865376 · DOI: 10.1186/s12906-021-03297-z