How necessary is vitamin D supplement? Have heard "most" are deficient, according to Drs. But most ppl get is from added synthetic D.?

Fortified foods. Most natural foods do not have it..some mushrooms have it if exposed to light. But ppl are said to get vit D from sun exposure. In the fortified foods, some brands get D from sheep wool, some from a lichen, some from types of yeast or mushrooms. So is this really necessary to add to food everyday,... show more Fortified foods. Most natural foods do not have it..some mushrooms have it if exposed to light. But ppl are said to get vit D from sun exposure. In the fortified foods, some brands get D from sheep wool, some from a lichen, some from types of yeast or mushrooms. So is this really necessary to add to food everyday, if ppls food normally doesn't naturally have it.. Most people I know don't eat sheep wool. Why would most still be deficient if it's added to food all the time.how can anyone know for sure if it's an exact science or all just theory.
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