Though we hear more and more about the benefits of vitamin D, few people know that magnesium is essential for it to work properly: in order for vitamin D to be able to fulfill its beneficial role, it needs to be converted several times, each transformation requiring magnesium. As magnesium deficiency is very common, we must consider whether we can are aggravating it by vitamin D supplementation alone.

Why is magnesium deficiency common?

With the advent of modern agriculture, the mineral and trace element content of arable land and thus food has declined significantly in recent decades, by about ~20% for magnesium. (1,2)

In addition, the modern Western-style diet contains increasing amounts of refined carbohydrates, oils and ultra-processed foods, which lose a significant proportion of important micronutrients during processing: refined grains, for example, contain only a quarter of the magnesium of whole grains, while white sugar and oil contain none.

Since magnesium is necessary for the function of hundreds of enzymes and many other biological processes, when it is deficient our body is unable to function properly. Studies suggest that up to ~80% of people do not reach the recommended daily intake of magnesium. (3)

D vitamin’s link to magnesium

Once vitamin D is produced in our skin, there are still many biological processes that need to take place before it can finally take effect.

The vitamin D3 (cholecalciferol) that is produced must first be transported to the liver, where it is converted into calcifediol, the stored form of vitamin D. This is later converted in the kidneys into the active form of vitamin D, which is calcitriol, and finally, for the beneficial effects of vitamin D to take effect, calcitriol must bind to vitamin D receptors in cells. (4)

The activity of the protein responsible for the transport of vitamin D, the enzymes involved in each conversion process, and the vitamin D receptors in the cells all require magnesium to perform their functions. (4) If a person supplements with sufficient vitamin D but does not consume enough magnesium, this process can stall at multiple points, rendering vitamin D ineffective. (5)

The synergy between magnesium and vitamin D

Severe magnesium deficiency, like vitamin D deficiency, can lead to rickets and extremely weak bones. (6) In these cases, vitamin D supplementation alone is ineffective, but supplementation in combination with magnesium can help to remedy the problem.

Magnesium deficiency reduces the number of vitamin D receptors in cells and the level of active vitamin D in the blood. (7) Like calcium, vitamin D increases the absorption of magnesium. (8,9)

In one study, people who had better magnesium intake had a much lower percentage of vitamin D deficiency than those who consumed less magnesium. (11) Accordingly, their risk of cardiovascular disease and colorectal cancer was much lower.

In an observational study, the risk of death increased by 60% in people with vitamin D deficiency whose magnesium intake was less than 414 mg per day. (12) Vitamin D levels alone did not affect the results so significantly, only when magnesium intake was also taken into account.

In a 2018 randomized trial, participants received an individually tailored amount of magnesium to reach their recommended daily intake and then tested to see how this affected their vitamin D levels. (13) For those with low levels (~30 ng/ml= 75 nmol/l), magnesium supplementation increased their vitamin D levels, while for those with higher levels, (~50 ng/ml= 75-125 nmol/l), it decreased them. This suggests that magnesium helps keep vitamin D levels in the optimal range: if too low, it increases its production, while if too high, it increases its breakdown.

Combined supplementation is much more effective

A 2022 randomized trial looked at people who were overweight and at increased cardiovascular risk. Participants were divided into 3 groups: the first group received 1000 IU vitamin D3 and 360 mg magnesium bisglycinate, the second group received 1000 IU vitamin D3 alone, and the third group received a placebo. At the end of the 12-week study, those who also supplemented with magnesium had the greatest increase in vitamin D levels, and only this group enjoyed a significant reduction in hypertension. (14)

A study in 2021 examined the combined supplementation of magnesium and vitamin D in women with vitamin D deficiency in terms of muscle strength/function and inflammation markers. Here, the participants were divided into two groups: one group received 50,000 IU of vitamin D and 250 mg of magnesium per day, while the other group received only vitamin D3. Participants who also received magnesium had a significant increase in grip strength and mobility, and a decrease in the levels of the inflammation marker CRP. (15)

The close relationship between magnesium and vitamin D could easily explain why vitamin D supplementation was highly effective in some studies and not in others; it is possible that the magnesium intake of the subjects may have influenced the results of the studies.

Summary

Micronutrients often work in synergy with each other to unfold their positive effects. We knew before that vitamin D works with calcium, vitamin K and vitamin A to maintain healthy bones and teeth, but it may have an even closer relationship with magnesium: if there is not enough magnesium, vitamin D does not work properly.

Since magnesium deficiency is very common, it is important to ensure adequate dietary intake, and vitamin D supplementation may be a good idea to take it as a supplement if you cannot get enough otherwise