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How to get vitamin d naturally 
Learn how the sun creates vitamin d. 
Sunlight is a form of radiation that has two forms, ultraviolet a (uva) and ultraviolet b (uvb) radiation. Your main source of vitamin d occurs when uvb radiation strikes your skin. When this happens, the first steps of vitamin d synthesis in your body is triggered.
After this, the next steps occur in the liver and then the kidneys. Because the rest takes place inside the body, once the body is triggered, you no longer need to be exposed to uvb radiation.