system
Given the following post, respond as if you're commenting on Reddit:
human
Why being exposed to sunlight “gives” us vitamin D?

I know it has to be with the cholesterol in our skin cells, but I don’t clearly understand how it happens.
gpt
Vítamín D is a hormone created by the skin as a reaction to ultraviolet radiation.

The skin cells absorb the UV and photolyzes protovitamin D3 into previtamin D3 (two compounds necessary for the creation of the essential hormone).

Pre-D3 then isomerizes into Vitamin D3, or else is further photolyzed into lymistrol and tachysterol.

Using sunscreen or living in Arctic areas can affect the body's absorption of UV light and the creation of Previtamin D3, lowering Vitamin D3 in the blood.