A nutritionist told my Mom years ago to start on Vitamin D for early osteoporosis as well as possible heart health ... then came immune system boosting. She takes one 1,000 IU gel cap twice a day and actually seems to help arthritis. I started a few years back for my knees and lower back. I don’t know if it’s psychosomatic but my knees do not ache as much and I don’t seem to catch a cold near as often ... but no solid evidence after that. Basically to me it might not help a lot but it has not hurt anything.
I don't supplement with a lot of vitamin D, but do take a multivitamin and some minerals on alternating days. I might look into supplementing more, especially in the winter time.