The vitamin D or D3 we take (cholecalciferol) is measured in mcg or micrograms or millionths of a gram (25mcg of D3 is the same as 1000iu)
calcidiol..a form of D in our blood and which we usually test for is originally D3 made from uvb sunlight reacting with a form of cholesterol in our skin. Fortunately , we can also get it from D supplements and some foods. D3 is then converted by the liver to calcidiol, carried by the blood and deposited in the liver,muscle and fat for future use. It is measured in nanograms or billionths of a gram/ mL(a mL is about a fifth of a teaspoon of blood) it has modest biological function
and finally the 1,25 form of D called calcitriol which is the very potent steroid form produced by the conversion of calcidiol (circulating D) to calcitriol (high test D)in our kidneys when instructed by the parathyroids(rice sized glands in the neck) by PTH or parathyroid hormone..The parathyroids sole duty is to monitor and regulate blood calcium. Calcitriol is measured in very minute amounts as picograms or trillionths of a gram/ml. Calcitriol can also be produced on a cellular level effecting vitamin D receptors throughout the body.
so each increases by a factor of 1000..one could loosely say the D3 (although it is not considered biologically active) we take as a supplement is about a million times less potent then the calcitriol produced by the kidneys..... Calcitriol in a topical form is what dovonex (a patentable analog of calcitriol) and vertical and silkis (which are actual calcitriol and natural so unpatentable) are based on...
i take about 2000- 4000iu/day of D,D3 or cholecalciferol (all the same) in summer/winter
hope this helps...bj
