Testing for the Vitamin D level

The easy blood test measures the concentration of 25-hydroxyvitamin D3, or 25(OH)D, the precursor produced by the skin and converted in the body to vitamin D. If one is over age 70, has darker skin, or lives at a northern latitude (far away from equator) or not regularly exposed to the sun or wear sunscreen, are at high risk of D-deficiency and should go for testing. People who have malabsorption problems or take medications that interfere with vitamin D activity (for example, glucocorticoids) should consider it as well.

However, some experts think testing is unnecessary as long as you get 800 to 1,000 IU of vitamin D a day. Deficiency is generally defined as a blood level less than 20 nano grams per milliliter, or 20 ng/mL (see chart). Levels that low have been linked to poor bone density, falls, fractures, cancer, immune dysfunction, cardiovascular disease, and hypertension. Many experts recommend a level of at least 32 nanograms per milliliter or 75 nmol/L and suggest that 800 to 1,000 IU of vitamin D per day is required to maintain that level.