Just about every patient I test is low in Vitamin D unless they’re supplementing with it (which by my standards means less than 40 ng/mL — the lab says less than 30 ng/mL is considered deficient). This is the case across the board, even though I live in AZ where it’s sunny all the time, and even with patients who tell me they spend a lot of time in the sun without or with minimal sunscreen.

So what gives?

Physiology 101 on Vitamin D

When we’re exposed to UVB rays from the sun, our skin creates 7-dehydrocholesterol. This enters the bloodstream and stops off of the liver, where it turns into 25-hydroxyvitamin D. (Alternatively you can eat 25-hydroxyvitamin D from fish, meat, eggs, and cheese.) This is the value tested on labs.

Then this version travels to the kidneys and turns into the more metabolically active form called calcitriol, aka 1,25 dihydroxyvitamin D.

Calcitriol’s main job is to increase calcium absorption from food.

But here comes the fun part: all of the nutrients in your body are connected to one another, either directly or indirectly. Tamper with one and you can cause repercussions elsewhere.

Also, keep in mind that your body is a living system, always seeking balance. So if, for example, your tissue levels of calcium are higher than they should be, your body may shut down calcitriol production in the kidneys to try to achieve that balance.

Why Tissue Burden of Calcium Might be High

Remember that study that came out a few years ago that suggested calcium supplementation could increase the risk of heart attacks? The concern here is that atherosclerotic plaques contain calcium deposits, and perhaps therefore taking calcium in supplement form will contribute to plaque formation. (This refers to non-absorbable forms of calcium taken by themselves, by the way, such as calcium oxide or sulfate, and not to absorbable forms found complexed with other factors for bone desposition or in multivitamins… but the idea that too much calcium can precipitate out onto body tissues is real. Here’s an article from Harvard that goes into this more.)

Why might we have too much calcium in our tissues, though, and not enough in our bones (since osteoporosis is rampant?) Largely due to our highly acidic diets, in the US which tax our blood buffering systems to the max. (Check out this article for more in-depth coverage of this topic.)

So basically our calcium is in the wrong place: it’s in our tissues rather than our bones. And maybe this dials down our vitamin D production: because our bodies are saying, “Stop with the calcium already!”

Vitamin K and Calcium

Vitamin K is another fat-soluble vitamin like Vitamin D, and its job is to allow the body to take calcium and use it in the clotting cascade. Vitamin K also produces a protein called osteocalcin, which puts calcium into the bones.

You get vitamin K1 from super-healthy veggies (broccoli, turnips, cabbage, cauliflower, and spinach), and then it gets converted to the active Vitamin K2 by the good bacteria in your gut. But alas, most of us aren’t eating those veggies, and we also don’t have nearly as much good bacteria in our guts as we ought to (and often we have a lot of bad bacteria instead). Here’s why this is the case. 

Result: too little vitamin K —> too much calcium in the tissues (rather than in the bones and clotting cascade, where it’s supposed to be.)

How Magnesium is connected to Calcium and Vitamin D

Like Vitamin D, magnesium also helps to regulate calcium levels, because magnesium and calcium have opposite effects. (Calcium and magnesium should remain in about a 2:1 ratio.) But if you don’t have enough magnesium, your tissue levels of calcium go up, too. 

Also, magnesium is used in the metabolism of Vitamin D, so too little magnesium can therefore lead to low Vitamin D, also.

But we’re chronically magnesium deficient as a culture. Largely this, too, has to do with dietary intake, as well as blood sugar dysregulation, and/or pharmaceuticals that deplete magnesium. (For more on this topic, check out this article.) 

Summary: Possible Reasons Why Your Vitamin D is Low

  • Your diet is crappy — not so much because it’s low in Vit D (though that’s probably true too), but because it’s acidic. This leads to too much calcium in your tissues, which leads to a feedback mechanism lowering Vitamin D. (Not that I’m judging you. 😉 If you want to eat less crappy, read here.) 
  • Your Vitamin K2 is low (perhaps leading to too much tissue burden of calcium). This also might be because your diet sucks, or because you’ve got dysbiosis.
  • Your magnesium is low. For more on what this looks like and what might cause it, check out this article.