Weather or not: the importance of vitamin D status monitoring and supplementation.

The Centers for Disease Control and Prevention's latest data show markedly high prevalence rates of severe vitamin D deficiency among Americans of all ages. Because of the numerous negative health consequences associated with vitamin D deficiency, we must consider all potential causes including insufficient exposure to the sun's ultraviolet B radiation. This article presents data from the National Weather Service that documents how few days in Minnesota offer the opportunity to make vitamin D. Thus, even Minnesotans who spend a significant amount of time outdoors and consider themselves to have sufficient sun exposure may still be at risk for vitamin D deficiency. This is especially true for the elderly, those with high melanin content in their skin, and those with a higher body mass index, all of whom require significantly more sun to achieve adequate levels of vitamin D. Given the lack of sufficient ultraviolet B radiation people in Minnesota get from the sun between October and April, measurement of vitamin D status is required for rational replenishment and maintenance dosing. The goal of replenishment should be at least 32 ng/mL and, ideally, more than 50 ng/mL.