it tests for various levels of vitamin D is in the body. vitamin D comes from milk and other foods, the sun and daily vitamins. D3 mostly comes from the sun. too much vitamin D can cause muscle spasms, and other bodily functioning problems.

you ever hear the saying ....Im achy, tired but my muscles want to keep moving (spasms, jumping, twitching restless legs syndrome) I think I got too much sun? there is such a thing as getting too much sun and too much laying under a tanning bed lamp. some people are actually allergic to the sun and can get too much Vitamin D3 in their body. I have MS. one of the things I have to do for it is maintain a good vitamins D levels.too much makes my twitching/spasming worse.