Vitamin D is one of the most important, essential nutrients for overall health. It actually functions more like a hormone than a typical vitamin, with receptors in almost every tissue in the body.
From an overall wellness perspective, it supports bone health, immune function, and cardiovascular health. From a fitness perspective, it even aids with muscle function and metabolism.
And yet, many people are deficient, often through no fault of their own. Living in a cold climate limits sun exposure, and the UV levels from the sun during winter months is low anyway. Skin tone, age, and even weight (obesity reduces the bioavailability of the vitamin D produced) can affect your ability to absorb vitamin D from the sun.
In addition, getting vitamin D strictly from your diet can be challenging. It’s not like vitamin C, which is prevalent in many fruits and vegetables. Fatty fish is really one of the only natural food sources of vitamin D.
So you may think – what’s the big deal, I’ll just take a vitamin D supplement.
Vitamin D supplementation helps, but sometimes isn’t enough. Research indicates that taking a vitamin D supplement often does not translate to increased vitamin D blood markers in a predictable way. This makes plausible sense when you realize that most vitamins and minerals work in conjunction with one another (and sometimes even oppose one another).
Now would be a good time to introduce another essential nutrient that many people lack, magnesium. We talked about the importance of magnesium in a previous article, but it’s relevant here as well. A study by Dai et al. suggests that magnesium may be the key to vitamin D levels.
It was an interesting study because the participants did not supplement with vitamin D at all, only magnesium. But what they found was that magnesium can regulate vitamin D levels in the body by itself.
Participants in the study who were low on vitamin D and supplemented with magnesium saw an increase in vitamin D levels.
Participants who were high on vitamin D and supplemented with magnesium saw a decrease in vitamin D levels, potentially preventing toxicity.
The magnesium dose was tailored to the individual, but the average was about 205mg. The type of magnesium used in the study was not stated, but magnesium glycinate is considered to be among the most bioavailable forms.
What this suggests is that magnesium doesn’t simply raise or lower vitamin D arbitrarily, it appears to help the body find its optimal level. The mechanism behind this lies in magnesium’s role in activating the enzymes responsible for vitamin D synthesis and metabolism. In other words, without adequate magnesium, your body may struggle to properly process vitamin D regardless of how much you get from the sun, food, or supplements. This could help explain why so many vitamin D supplementation trials have produced disappointing or inconsistent results.
Here is the key takeaway: if you are trying to optimize your vitamin D levels, magnesium is worth addressing first or at minimum alongside it. Given that nearly 50% of Americans are already falling short of their recommended magnesium intake, there is a good chance you are one of them. Magnesium is so important by itself that it’s probably worth taking as a standalone supplement anyway. Its ability to aid in vitamin D status is just another added, yet important, bonus.
This story was originally published by Men’s Fitness on Apr 7, 2026, where it first appeared in the News section. Add Men’s Fitness as a Preferred Source by clicking here.
