This has been an ongoing issue for me even under circumstances where I should be getting enough D from sunlight etc. Without supplementation (at at least 2000-4000 IU/day) my levels plummet even with daily sun exposure (without sunscreen etc.). We just had two of our kids tested partly because of this. They are both on GF diets (as am I) although no positive test, but dramatic dietary response. GI Dr. is the one that ordered the D tests. Just got a call and based on their normal range of 13-67 my daughter came back as less than 4! Sons tests are not back yet, but his calcium was slightly low and he takes calcium supplements consistently and has taken 600 IU of D daily in his supplements for years now. All are D3 so that's not the issue. They both get lots of sun, I use sunscreen only in areas likely to severely burn, they're very fair skinned and there is just no good reason for this. Has anyone ever dealt with anything like this? A big part of the reason for getting them tested was concern over my issues with chronic low vitamin D so we wanted to make sure they were o.k. My oldest needs to be tested yet and has been complaining of sleep issues, brain fog, lack of concentration, fatigue etc. which I am now wondering if it's low D. She is darker skinned so she was actually my biggest concern, but my Dr. didn't want to test. Calling right now to ask him to order it and given the situation I can't imagine he'd refuse!