The relationship between environmental factors and the prevalence of vitamin D deficiency in Iran

Vitamin D deficiency is one of the major health problems that is unexpectedly prevalent in Iran. The ultraviolet (UV) rays of the sunlight are the most important source of vitamin D in humans. In contrast, environmental factors are one of the reasons for decrease in UV transmission to the earth which results in the reduction of vitamin D absorption. Since the role of environmental factors has been neglected in studies related to vitamin D deficiency; therefore, the present study aimed to investigate the relationship between environmental factors, such as geographical and air pollution parameters, with prevalence vitamin D deficiency in Iran. In this study, the years of the vitamin D deficiency prevalence were extracted from different studies for different cities of the country where vitamin D deficiency was reported. Then, the environmental factors, which affect the sunlight transmission through the atmosphere, were collected for the place and time of vitamin D deficiency that mentioned in the studies via different geographic databases. Then, the relationship between environmental factors and prevalence of vitamin D deficiency was determined. Finally, a total of 35 studies were completely reviewed. The results showed that there was a significant relationship between the prevalence of vitamin D deficiency andenvironmental factors such as cloudy and clear days. However, there was no significant relationship between vitamin D deficiency and other environmental factors such as geographic (sunshine, longitude, latitude, elevation, humidity, and temperature) and air pollution parameters (number of days with dust and visibility less than or equal to 2 km).