I always have low vitamin D if I don't supplement. I have treatment resistant depression as well as anxiety and insomnia and getting my vitamin D level to a normal level has never helped any of those things. I know how important it is for our bodies so I continue to supplement; it might be worth a try for you? Please make sure that if you do supplement, you get regular bloodwork to make sure you're not over-supplementing. I had a PCP put me on a huge dose and I ended up with vitamin D toxicity, which was quite unpleasant.