For me, I noticed my joint pain, in the SI joint, increasing as the season shifted into Fall/Winter. I started LDN a few months later, hoping this would help; however, it didn't help me much in that department. Not until I started taking 5000iu D3, daily, did I see sustained improvement of joint pain.
For me, my joint pain is DEFINITELY tied directly to D3 levels, though I've never been tested. I do have paper work to get the labs done; I just don't know how much it is, but I'll spring for it eventually. I still take 5000iu D3 daily, but every couple months I may have a couple hours of SI discomfort, as opposed to the 2-5 day streaks I was having. So, perhaps, I may need to take more every so often--it is pretty hard to overdo D3. Not once since supplementing daily throughout the Fall/Winter months this year has my pain been bothersome for more than a couple hours--I mean, like one time in the past 4 months. Huge improvement compared to last year.
I do know a Lymes patient who accredits LDN with stopping her unbearable joint pains that left her bedridden for days on end.