I cannot understand Dr. Cooper's position. Thirty minutes in the summer sun will produce around 10,000 IU. That seems like a natural level if you spend 30 mins every day, which is what is recommended. If you live at a higher latitude (- or +) then you will hard pressed to spend every day or even every fifth day in the sun for 30 minutes. In fact most people would not even spend every fifth day. That is why levels are around 20ng/ml. So a person supplementing with 2000IU is certainly not a "crazy" level. It is exceedingly moderate. This is why, for people at high latitudes, during the winter, 5000IU is a necessary compromise and far from crazy. You will eat your words Dr. Cooper.
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