What is “Vitamin D”

Vitamin D has received a lot of attention over the past decades, because of the extensive health-related research that has been published on it. Vitamin D, also called the sunshine vitamin, is a fat-soluble vitamin that is produced mainly when the skin comes into contact with the sun’s UV radiation. There are approximately 2,700 binding sites for vitamin D in the human genome (DNA), which suggests that vitamin D exerts influence on various nearby genes associated with autoimmune diseases.

There are two main forms of vitamin D that are taken from food or supplements –ergocalciferol, also known as D2, and cholecalciferol, or D3. Vitamin D3 is converted into 25-hydroxycholecalciferol in the body, and then 1,25-dihydroxyvitamin D (calcitriol) in the kidneys. Calcitriol is the most potent and active steroid form of vitamin D3, but is generally not measured unless an individual has kidney disease or if there is reason to believe the body is not converting the vitamin into its active form.

Vitamin D plays an important role in the absorption of calcium from the intestines and is vital to bone strength. Measured in nanograms per milliliter (ng/mL), adult ranges of vitamin D may be found in the table below. Reference ranges for high and low values may vary according to the lab, so be sure to look at the ranges provided on your blood test form. Although getting vitamin D count on a routine blood test is becoming more popular, not all doctors request it. Make sure to ask your doctor to include this marker when you get your blood drawn.