Vitamin D3 is produced on the skin by ultraviolet radiation (UVB 290-315nm). Its production on the skin accounts for about 80% of the total daily production, while the remaining 20% ​​comes from the food.

The production of vitamin D in the skin is affected by many factors:
• Sun exposure
• The use of sunscreen (sunscreen with a protective index> 8 restricts up to 90% of the vitamin D composition)
• Clothing (covered body ends)
• The amount of melanin (the black tribe has lower levels of vitamin D)
• At the time of the year (significant fall in winter months)
• Latitude (the increase in latitude, ie from the equator to the poles, limits the vitamin D synthesis capacity)
• The age (the elderly have reduced production capacity)
• Obesity (vitamin D is absorbed by adipose tissue)
• Atmospheric pollution (mainly in urban centers there is reduced UV radiation)