I have also struggled with depression for a long time. I've been on just about every antidepressant they make starting in my 20s with Elavil if anybody remembers that one! So about five years ago my therapist, a psychiatric nurse practitioner, wondered about my vitamin D level. When she checked it was low, in the 20s. She told me to start supplements right away. After a few months of supplement it came up to the normal range. However I've done a lot of reading on vitamin D and the immune system. There are a lot of infectious disease physicians and researchers who feel like the normal range as it stands now is too low. As an aside, there is a lot of research on how vitamin D can be very helpful for your immune system and it was used extensively during the Covid pandemic. A lot of people who did not want the shot increased their vitamin D intake among other things and they did not get Covid although who knows if it's related. But interesting. They suggest taking vitamin D and to try and get your level as far above the 50s as you can. I don't want to suggest that you do this because that's not my place. I can say that what I'm doing is taking 10,000 units per day and my vitamin D level is definitely in the 50s. I can say that it helped a lot and I continue to take that every day. Recently I learned that you should be taking a supplement called K2 along with the D it helps absorption apparently. They do make that in a combination pill. I hope this helps a little? At least you know that it's not uncommon for mental health providers to focus on that as one of their diagnostic tools. I wish you the best. Talk to your provider about taking high doses of vitamin D. They do make a 10,000 unit version so it's not like you have to take multiple doses. Merry Christmas!