Daughter and I both have super high B12, which doesn't come down easily even if we stop taking B12. I thought humans excrete excess B12, but we certainly don't seem to be doing so. We both also have low D that does not increase easily even with high doses of sublingual D. I have been taking at least 5000 IU daily. In 8 months last year that dose increased my D levels by 20 ng/ml. In the 9th month I cut back to 2500 IU daily and my level dropped 5 ng/ml in a month. Now I'm back to 5000 IU daily, so hopefully we'll stop this downward trend. This looks mighty weird to me, but I don't know much about vitamin D. Anybody have any ideas? We're both hypothyroid, too. I have no idea if there's a connection there at all. Can anyone bring some insight into this persistent high B12, low D situation?