How much vitamin D should I take?
Ask the doctor
What's the evidence that — besides reducing the risk of certain bone diseases — there is any other health benefit from taking vitamin D supplements? Some people argue that modern-day humans might be vitamin D deficient, relative to our ancestors. Why? Because our species and its immediate predecessors have been on earth for several million years, spending a lot of time outdoors, soaking up a lot of sun and making a lot of vitamin D. Then, only about 100 to 200 years ago, those of us in the developed nations (like the United States) began to spend our days largely indoors. Therefore, our levels of vitamin D are probably lower than those of our ancestors. (We can't know that, since they didn't test for vitamin D 100 years ago.) It's plausible that such a sudden change in our biology might have adverse health effects.
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