Seven years ago, at age 27 my endo insisted I take a multivitamin to ensure I was getting enough vitamin D.  The issue I had was steroid induced osteoporosis, from the prednisone medication I was taking at age 6 when I was first diagnosed with CAH.  The vitamin D apparently is essential for calcium absorption.   Ask your endo about it.  I was on pred for a long time, now I’m on cortisone acetate which apparently has less side effects.