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daywalkker t1_izj05qy wrote

Your physiology still requires sunlight to activate the vitamin D. You can drink all the vitamin D fortified milk you want, but if you completely avoid sunlight, you will be deficient in the active form of vitamin D.


PyroDesu t1_izjb20k wrote

Not true!

Sun (or more specifically, UV-B) exposure only generates the inactive cholecalciferol, the same stuff you can get from diet (diet can also give you ergocalciferol, the plant-based version, which works too). The activation process is two enzyme hydroxylation steps, first in the liver and second in the kidneys.