system
Given the following post, respond as if you're commenting on Reddit:
human
How do we get vitamin D from being in sunlight?

Title says it all. Thanks.
gpt
Cholesterol is synthesized into 7-dehydrocholesterol, which when exposed to UV light becomes vitamin D3 (cholecalciferol).  This is further modified by the liver into 25-hydroxy vitamin D (calcifediol), and by the kidneys into 1,25-dihydroxy vitamin D (calcitriol), which is the most metabolically active form.  The last step is under regulation by parathyroid hormone, since vitamin D affects calcium homeostasis.