I have been nagging friends and family to get Vit. D testing for years.  I really feel American doctors are missing a critical part of staying healthy.  The media call it the "sunshine vitamin" so people think if they are in the sun they will absorb it.  Not everyone does absorb it.  A study of California surfers showed most of them were low or sub optiminal.  Regular doctors think a bottom number is normal.  Yet, is it optimal?  The levels are to prevent scurvy.    Remember, your history class told you the sailors ate limes and were called "limeys" to prevent scurvy.  Yet, is preventing scurvy our only goal?  What about preventing colds, flu, Covid 19, etc?  Here is a link to a great group that really believes in optimal Vit. D for the best health.  Of course, Vit. D is one of the fat soluble vitamins that celiacs (and others) malabsorb. The link is not copying.  It is GrassRoots Health.  I will try again.