With lots of discussions on Vit D, I thought this page might be helpful. They have explained in a very lucid manner.
I will soon also write a small topic on how doctors replace Vit D3, so all of you have an idea. It's very essential to know, because unlike other vitamins, body does not have a method to throw out extra Vitamin D and excess Vitamin D can lead to toxicity as well. So we need to ensure to keep our levels within range. It's really simple if we follow the standard protocol.