With all this interest in vitamin D, you want to be sure that you have enough in your blood. If not, you want to make sure that you build up your level to the right amount. So what is the right amount? You determine the level of vitamin D by doing a blood test for 25 (OH) vitamin D. That’s 25 hydroxy vitamin D. Most experts agree that a level of 32 nanograms per milliliter (ng/ml) in the blood is optimal for bone health but no one agrees on what is optimal for immune health, heart health, cancer health and all the other important functions that vitamin D appears to have.
Your skin, where vitamin D is made, has a wonderful system for making the right amount, then shutting off further production. I have one patient who is a beach volleyball player. Although he assures me that he wears sunscreen and administers more every four hours, as he should, I feel certain that there are times, in the heat of a match that he forgets to re-cover his skin. His blood level of 25 (OH) vitamin D is 42 nanograms per millileter so perhaps that is the optimal level that our body wants us to have.
You can build up your vitamin D by allowing your arms and legs but not your face to be exposed to the sun for 15 minutes three times a week between the hours of 10 AM and 2 PM. But if you can’t get out in the sun or you live at latitude 37 degrees or above, about where San Francisco is located, you won’t get much vitamin D in the winter. Then you need to take a supplement.
The next question is how much supplement do you need to get to 32 nanograms per milliliter? Of course it depends on where you start. Let’s say you are at 20 ng/ml. Studies have shown that consuming 40 international units (IU) of vitamin D will raise the 25 (OH) vitamin D by 0.4 ng/ml. You want to raise it 12 ng/ml. Dividing 12 by .4 gives you 30. Multiplying 30 by 40 gives you 1,200 IU. To be sure, you can take 2,000 IU daily and you will know that you are achieving your goal. You don’t have to worry about taking too much. That low dose is very far from a dose that would cause toxicity.
If we find out that a level of 40 ng/ml is ideal for all functions of vitamin D, that 2,000 IU will be just right.