By Kelly Parcell, ND According to the CDC up to one quarter of the population is deficient in vitamin D. Many people are on the low end of normal as well. Vitamin D is perhaps the single most underrated nutrient in the world. Even in Boulder many patients are low! The reason has a lot to do with sunscreen in the Summer and layes of clothing in the Winter. As we move into Winter in Colorado, it's a good time to have your vitamin D level checke...