Vitamin D: Why We're Lacking It & How to Get More of It! by Donna John
The reason we're lacking vitamin D nowadays is because we're missing out on the No. 1 source: the sun.
"Vitamin D is a pro-hormone made in the skin upon exposure to sunlight, and production of it is rapid and robust," says Dr. Christopher Calapai. "Within 10 to 20 minutes without wearing sunscreen, people make between 10,000 and 20,000 IU. But because of widespread sunscreen use, total sun avoidance and our increasingly indoor lifestyles, our vitamin D levels have fallen drastically."
Dr. Calapai recommends at least 2,000 IU per day, year round.