vitamin D
what does your body convert into Vitamin D when you are in the sunlight?
cholesterol !
Most vitamin D is naturally derived from sunlight exposure. The ultraviolet rays convert 7-dehydrocholesterol in the skin to cholecalciferol, which is an inactive form of vitamin D. The kidneys then convert cholecalciferol to 1,25-dihydroxycholecalciferol, which is active and able to perform normal physiologic functions. When levels of calcium in the blood decrease, the kidneys make more calcitriol.
https://www.wisegeek.com/what-is-calcitriol.htm