Originally Posted by captjane
vitamin d doesn't require fasting and can be done at any time during the day.
It takes significant time to deplete or build up Vit D levels. I believe the half-life or time to reduce one's D levels by half is on the order of 4-8 weeks. And from what I've read in Dr. Michael Holick's book is that Vit D from sunshine lasts longer in the body than oral supplements. There shouldn't be much of a change in your Vit D during just one day even if you received 10,000-20,000 IU worth of Vit D the day before from the sun or received 0 IU.