system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come it’s nearly impossible to get vitamine D overdose from the sun, but you can from supplements?
gpt
The sun is used to convert a vitamin D precursor to the next metabolite in the process. The body doesn’t store enough of the vitamin D precursor to cause an overdose. It also isn’t the final “activation” step for vitamin D.