Can You Take Vitamin D and Magnesium Together?

If you take vitamin D, you may have been told you also need magnesium. Or you may be wondering whether taking both is even safe. Here is a plain answer.

The short answer

For most healthy adults, yes. Vitamin D and magnesium can be taken together, even in the same sitting. They do not compete with each other for absorption in any way that matters. In fact, they work as a team.

Why they are often paired

Your body has to convert vitamin D into its active form before it can use it. Several of the enzymes that do this work need magnesium to function. This means that if you are low in magnesium, vitamin D may not work as well as it could.

This link is real but still being studied. Most of the evidence so far comes from observational studies and small trials, so it is fair to say the pairing is promising, not proven to be a must-do for everyone.

How to take them

• Vitamin D is fat-soluble. Take it with a meal that contains some fat (eggs, avocado, yoghurt, nuts, oily fish) to improve absorption.
• Magnesium is often taken in the evening, because some people find it relaxing. Take it with food if it upsets your stomach.
• You do not need to space them apart. Taking both with dinner is perfectly fine.

Which type of magnesium?

• Magnesium glycinate: usually gentle on the stomach.
• Magnesium citrate: well absorbed, but can loosen the bowels.
• Magnesium oxide: cheap and common, but poorly absorbed and the most likely to cause diarrhoea.

How much?

These are general adult limits, not personal recommendations:

• Vitamin D: most adults need roughly 600 to 800 IU (15 to 20 mcg) a day in total. The commonly used upper limit is 4,000 IU (100 mcg) a day from all sources. More is not better, and very high doses can raise calcium in the blood to unsafe levels.
• Magnesium from supplements: the commonly used upper limit is 350 mg a day (this applies to supplements, not food). Going over it mostly causes diarrhoea and cramps.

Your own needs can be different. A blood test and your pharmacist or doctor can tell you more.

Who should be careful

Talk to your doctor or pharmacist first if you:

• have kidney disease, because the kidneys clear magnesium and vitamin D can raise calcium
• have a history of kidney stones or high calcium levels
• are pregnant or breastfeeding
• take medicines (see below)

Medicines to check

• Some antibiotics (for example tetracyclines and quinolones), bisphosphonates (for osteoporosis) and levothyroxine (thyroid): magnesium can reduce how well they are absorbed. Your pharmacist can tell you how many hours to leave between them.
• Thiazide diuretics ("water pills"): together with high-dose vitamin D, these can push calcium too high.
• Digoxin and some heart rhythm medicines: magnesium and calcium levels matter, so ask before supplementing.

The bottom line

For most healthy adults, vitamin D and magnesium are a sensible, safe pairing. Take vitamin D with a fatty meal, choose a gentle form of magnesium, stay under the upper limits, and check with a pharmacist if you take regular medication.

Want to check your own list?

Use the free Interaction Checker on VitaGuide to see whether your medicines and supplements may interact, or email our pharmacist for a review.

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This article is general information and not medical advice. It does not replace advice from your own doctor or pharmacist.

Sources to verify before publishing: NIH Office of Dietary Supplements fact sheets on Vitamin D and Magnesium; published reviews on magnesium and vitamin D metabolism.