Biosynthesis Vitamin D3 is the product of solar ultraviolet irradiation of 7-dehydrocholesterol in the skin So 7-dehydrocholesterol is also called provitamin D3 Vitamin D, is the product of solar ultraviolet irradiation of ergosterin in the skin So ergosterin is also called provitamin D2Biosynthesis • Vitamin D3 is the product of solar ultraviolet irradiation of 7-dehydrocholesterol in the skin. So 7-dehydrocholesterol is also called provitamin D3 . • Vitamin D2 is the product of solar ultraviolet irradiation of ergosterin in the skin. So ergosterin is also called provitamin D2