Dear coffee drinkers, this is for you . . . and me.  From Dr. Jack Kruse, 

So, if you drink a lot of coffee, I have some news for you... you need even more sun. Caffeine drops your sulfated Vitamin D3 levels because it dehydrates our bodies, and there is even data out that ruins the Vitamin D receptor function. Caffeine is well known to decrease your VDR production. You may need more AM oyster shooters!!!! https://www.ncbi.nlm.nih.gov/pubmed/17223552.