Estimated ultraviolet exposure levels for a sufficient vitamin D status in northwestern Iran

Introduction: Normal exposure to sunlight results in the production of vitamin D in human body, which happens because of the interaction between ultraviolet radiation and cholesterol in skin. Exposure to sunlight is responsible for 90 percent of vitamin D needed for the body. Studies show that Iran is a country with high percentage of lack of vitamin D (83 percent). Based on previous studies, it has been estimated that if 25 percent of human skin get exposed to sunlight (head, neck, hands and arms), enough vitamin D can be synthesized. In a new definition this amount of vitamin D is called Standard Vitamin D Dose (SDD). In this study the SDD has been calculated and predicted for people who live in Tabriz.   Materials and Methods: First, the amounts of UV type A and B by handheld lux UV-IR meter, for a whole year from sunrise to sunset were measured in Tabriz during 2016-2017. UV indexes were calculated. Skin type of people in Tabriz can be classified in type five (which is specific to people live in Middle East). For this type of skin Standard Vitamin D dose is 260j/m2. Therefor based on existing studies, the relation between ultraviolet index and standard vitamin D dose per hour can be described as follows: 1 SDD = 40 ∗ (260/3600) W/m2 = 2.89UVI Hour Now by dividing UVI measured for every hour, standard vitamin D dose for those hours can be obtained. Note that SDD=1 means by exposing a quarter of human skin to sunlight, the necessary amount of vitamin D can be synthesized in the skin. Results: We can observe that there is a significant difference between the amount of ultraviolet radiation in different seasons, months and hours of the day. During the day, the most amount of radiation can be found in midday, and in all months of the year we can see a good SDD during this period of time. Between the hours of 10 am to 15 pm in all months of the year, the sun light intensity can be reached in less than an hour to meet one SSD.   Conclusion: The results show that the intensity of ultraviolet radiation is capable of supplying enough vitamin D during year.