Why You Should Take Magnesium with Vitamin D
- , by SANUSq Research team
- 9 min reading time
You're diligently taking your vitamin D — but without enough magnesium, your body may struggle to actually use it.
A partnership, not a solo act
Nutrients rarely work in isolation, and magnesium and vitamin D are a perfect example. Many people take vitamin D on its own, unaware that magnesium is essential for the body to convert vitamin D into its active, usable form. Without adequate magnesium, even a generous vitamin D intake may not deliver its full benefit — the raw material is there, but the machinery to activate it is running short.
It's worth following that machinery through, because it makes the point better than any general statement about teamwork. Vitamin D from sunlight or a capsule is not active as it arrives. It is converted twice: once in the liver, into the storage form that a blood test measures, and again in the kidneys, into the active hormone that actually does the work. Each of those conversions is carried out by an enzyme, and enzymes need cofactors. Magnesium is the cofactor here, which is why a shortfall of it slows a process that has nothing obviously to do with magnesium at all.
All of the enzymes that metabolise vitamin D require magnesium as a cofactor; magnesium assists in the activation of vitamin D, and low magnesium status is associated with impaired vitamin D metabolism (Uwitonze & Razzaque, 2018).
Why this matters in practice
This partnership has a real, practical implication. If you're supplementing with vitamin D but are low in magnesium — which, as we discuss in the benefits of magnesium, is surprisingly common — you may not be getting the return you expect from your vitamin D. Worse, some evidence suggests that taking high-dose vitamin D while magnesium-deficient can further deplete magnesium, as it's used up in processing the vitamin D. Ensuring you have enough of both makes each work better.
The relationship runs both ways
Interestingly, the interaction is mutual: active vitamin D can, in turn, help the body absorb magnesium from the gut. So the two nutrients support each other in a virtuous cycle — another reason they're such natural companions, and why magnesium is worth considering alongside the vitamin D and K2 pairing covered in our bone and heart articles.
Why magnesium runs short so often
The reason this pairing matters at all is that magnesium intakes are frequently on the low side, and for reasons that have little to do with anything a person is doing wrong. Magnesium sits in the green parts of plants and in whole, unrefined foods, and refining removes a good deal of it — white flour and white rice carry far less than the wholegrain versions they came from. Diets built largely on refined and processed foods therefore tend to run lower than diets built on nuts, seeds, pulses and greens. Losses can also be higher in people who drink heavily, and some prescribed medicines increase magnesium loss, which is one of many good reasons to keep your pharmacist in the loop.
There is also a measurement problem that catches people out. Only a small fraction of the body's magnesium is in the blood at any time — the great majority sits in bone and inside cells — so a normal serum magnesium result does not necessarily mean stores are ample. This is a genuine limitation rather than a reason to assume you are deficient, and it is one to discuss with your doctor rather than to resolve yourself.
What else magnesium is doing
Activating vitamin D is only one item on a long list. Magnesium is a cofactor for a large number of enzyme reactions, and it has a particularly close relationship with energy: the ATP that powers your cells is biologically active bound to magnesium, so essentially every transaction in your energy economy involves it. It is also central to how muscles work, since contraction and relaxation depend on the movement of calcium and magnesium, and to the electrical signalling of nerves. And around half of the body's magnesium is stored in bone, where it forms part of the structure alongside calcium.
Set those roles beside vitamin D's own contribution to calcium handling and bone health, and it becomes clear the two are not just chemically linked but working towards several of the same ends.
What this doesn't mean
Two clarifications, so this isn't over-read. First, magnesium is not a substitute for vitamin D, and no amount of it will make up for having none. The point is the opposite: magnesium is what lets the vitamin D you have do its job. Second, none of this is an argument for large amounts of either. Being adequately supplied is the goal, and more than adequate is not better — magnesium in excess of what the body needs is largely dealt with by the bowel, which is why an oversized dose announces itself unpleasantly.
Anyone with reduced kidney function should be more careful still, because the kidneys are what clear surplus magnesium, and should not start a magnesium supplement without medical advice. The same is true if you are on prescribed medication of any kind, as timing and interactions can matter.
Getting both
Magnesium is found in nuts, seeds, leafy greens, legumes and whole grains, while vitamin D comes from sunlight, oily fish and fortified foods. Because both are commonly under-consumed, some people choose to supplement.
If you go that route, a few practical points help. Magnesium comes in several different compounds, and they are not interchangeable: the more soluble organic forms are generally better absorbed, while cheaper inorganic forms such as magnesium oxide are absorbed less well and are more likely to loosen the bowels — which is precisely why some of them are sold as laxatives. Taking magnesium with food, and splitting it rather than taking it all at once, is gentler on the gut. Vitamin D, being fat-soluble, is best taken with a meal containing some fat. Products are sold both as single nutrients and as combined magnesium vitamin D3 formulas; either approach is fine, and the choice is mostly about how many things you want to remember to take.
For readers pairing the two, SANUSq offers liposomal Magnesium to go alongside a liposomal Vitamin D3 + K2.
Frequently asked questions
Why take magnesium with vitamin D?
Magnesium is required by the enzymes that activate vitamin D, in the liver and then the kidneys. Without enough magnesium, your body can't fully use the vitamin D you take, so the two work far better together than either does alone.
Can low magnesium make vitamin D less effective?
Yes. Because magnesium is a cofactor for activating vitamin D, low magnesium can impair vitamin D metabolism, potentially blunting its benefits even if your intake is adequate.
Does vitamin D affect magnesium?
The relationship is two-way: active vitamin D helps the gut absorb magnesium, while magnesium helps activate vitamin D. Some evidence also suggests high-dose vitamin D can use up magnesium when magnesium is already low.
How much magnesium should I take with vitamin D?
There's no single figure — it depends on your diet and needs. Aiming for a good dietary magnesium intake is the foundation; your healthcare professional can advise on supplementation.
What foods provide both?
Magnesium comes from nuts, seeds, greens, legumes and whole grains; vitamin D from oily fish, egg yolks, fortified foods and sunlight. A varied diet supports both, with supplements filling gaps.
Does a normal blood test rule out low magnesium?
Not entirely. Only a small share of the body's magnesium is in the blood, with most held in bone and inside cells, so a normal serum result doesn't guarantee generous stores. It's a limitation worth discussing with your doctor rather than reading either way on your own.
Which form of magnesium is best?
The more soluble organic forms are generally better absorbed, while cheaper inorganic forms such as magnesium oxide are taken up less well and are more likely to loosen the bowels. Taking it with food and splitting it through the day is gentler on the gut.
Is there anyone who shouldn't take magnesium?
Anyone with reduced kidney function should not start a magnesium supplement without medical advice, since the kidneys clear the surplus. If you take prescribed medicines, check with your doctor or pharmacist, as timing and interactions can matter.
Help your vitamin D work
Pair your vitamin D with the mineral it needs — our liposomal Magnesium.
References
- Uwitonze AM, Razzaque MS. Role of Magnesium in Vitamin D Activation and Function. J Am Osteopath Assoc. 2018;118(3):181-189. PMID 29480918
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The team at SANUSq.
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The health information in this article is provided for educational purposes only. Consult your healthcare professional before making any medical decisions.
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