What is Vitamin D and why is it so important?

Achy, Weak Muscles

Muscles rely on certain amounts of vitamin D in order to function properly. When the vitamin is not there, this can cause sore, achy and weak muscles. The is the kind of feeling you often get when you have a viral infection like the flu.  The pain can vary from fairly mild to severe and tends to get worse over time if the deficiency is not corrected.