@fdixon63, Here are some sites to read about supplementing with Vit D. https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-how-much-vitamin-d-do-i-need/ and https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/vitamin-d-deficiency/faq-20058397 You can find many more articles on the Mayo site by Googling Vitamin D Mayo Clinic. There are many more. I do not use any supplements because I just cannot stay on schedule with them. I try to get as many of my vitamins from my food. I do know that it is suggested that you take a combination supplement of both Calcium and Vitamin D. Your body cannot absorb the D without the calcium.