According to researchers, most experts agree that a minimum amount of 1,000 IU of vitamin D3 per day is necessary to maintain circulating concentrations of 25 (OH) D.
It is already known the fact that provitamin D3 production varies, depending on several factors, including skin type and weather conditions. Excessive exposure to sunlight does not lead to vitamin D intoxication, because provitamin D3 and vitamin D3 are photolysed by a few photoproducts.
During winter, at high latitudes, provitamin D3 production is minimal. Excessive skin pigmentation, application of sunscreens, aging and clothing have a dramatic effect on the production of vitamin D3 in skin. It was assumed that people living at higher latitudes have a greater ability to synthesize vitamin D3 because there is less ozone to absorb the UVB photons.