Vitamin D is essential. Or at least that’s what we all thought. Wudan Yan, for the New York Times, writes about the mystifying case of a patient with no detectable circulating vitamin D in her blood. The woman had bone disease, but experts thought that with her condition, she should be dead. Read Wudan’s story to learn how University of Washington scientists finally reconciled their data with the living patient before them. It’s lesson for all of us about vitamin D and health. @wudanyan, image: Henry Gray