Vitamin D studies seem to take pride in using different terminology which makes interpretation challenging. For example, the level of vitamin D in a supplement or food can be measured in:- International Unit (IU)
-
- Milli Centi grams (mcg) - this is the same as micro grams but written differently. For the life of me I don't know why they do it.
Then they have a term called minimal erythemic dose (MED). This is the maximum amount of vitamin D you will produce in a single exposure to UV rays. This occurs at the point just before you are going to get sun burnt. Typically it is 10 - 20 000 IU's which is a rather large range.
Then you can measure vitamin D in the blood. The following are units are ones used in papers:
- nano grams per ml (ng/ml). This is the weight of vitamin D in a ml of blood. Clearly this is a low amount.
- nano mole per liter. (nmol/L). This is the number of vitamin D molecules in a liter of blood. To convert between ng/ml and nmol/L you multiply by 2.496. (or multiply by 1/2.496 going other way)
Type of vitamin D in the blood. Most studies measure 25-Hydroxyvitamin D which is commonly know as vitamin D3. Yet other studies measure 1,25-Dihydroxyvitamin D which is vitamin D2. Both of these are biologically active and in the liver vitamin D2 is changed into vitamin D3. Vitamin D3 is made in your skin, where as vitamin D2 comes from plant matter in your diet. So some studies look at both types, others just one. That said D2 is at lot lower levels with units of pico grams / ml (pg/ml) and pmol/L with conversion factor of 2.6
Therefore is it no wonder that the general public are confused. I would argue that even doctors would be confused by all this, given that they are pressed for time and don't have the energy to labor through such conversions.
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