Comment by dns_snek

I don't know why this is downvoted, I had a very similar experience a while back. I took 4000 IU/day for about 4 months, insignificant sun exposure and ended up at 60 ng/mL (lab listed normal range as 30-40).

My starting levels were unknown but I assumed they were low given my usual sun exposure and some low-energy symptoms (which resolved a couple of weeks after I started taking it). I discontinued VitD then and now I only take 1000 IU/day in the winter.