According to my former GP, vitamin D can fall below recommended levels over the winter months if you haven't stored up enough of it during the summer. So it's a

According to my former GP, vitamin D can fall below recommended levels over the winter months if you haven't stored up enough of it during the summer. So it's a matter of months not days. As I understand it, vitamin D first goes into the blood. Any excess is then stored in your body fat and in your liver where it can last for months. So I'm thinking that taking supplements right before a blood test could be a bad idea. But that doesn't mean depletion of stored up vitamin D happens within hours. It definitely does not.