Garland: It's actually quite wise for physicians to order that test for their patients once a year. Preferably in March when the vitamin D is typically lowest of all times of year and if it isn't up to 60 nanograms per mil, that is an indication of the need for supplementation and it's at that level in less than five percent of the population now.
Narrator: Garland adds that patients who are genetically predisposed to breast or colorectal cancer may not be able to metabolize vitamin D in a way that allows it to be effective. So, they may be good candidates for taking vitamin D under physician supervision. For Science Today, I'm Larissa Branin.