Is Sun a source of Vitamin D?- Physics Problem #4

My mom and I often debate over the scientific significance of many ancient traditions and beliefs. One such debate started last month when she complained about me spending my whole day inside a closed room and that sitting in the Sun is very important because it helps produce Vitamin D. I jokingly countered by stating that exposure to Sun causes Cancer too. Then I realized that actually I know nothing about this. Why is it that morning Sun is good for health and afternoon Sun is bad if Sun is the same in the end? I went to Google Scholar and found the answer. You will find it in this video.