This review provides an updated overview of global vitamin D status. In areas with available data, the prevalence of low vitamin D status is a global problem in all age groups, even in countries with sun exposure all year round. It is important to note that the problem is greater in the Middle East, particularly in girls and women. The data also pinpoint the regions with missing data for each specific population groups. There is a striking lack of data in infants, children and adolescents, and in most countries of South America and Africa.
In general, this high prevalence of low vitamin D status may be related to several issues, such as less vitamin D photosynthesis in response to UVB in individuals with high skin melanin content or due to aging, use of extensive skin coverage and scarce exposure to sunlight, which has often been described in individuals from Africa, the Middle East and Central and South America. Moreover, a low vitamin D intake and high rates of obesity worldwide can also contribute to the problem. Season appears to be a small component to the problem worldwide, as countries with long winters have less deficiency rates overall compared to sunny countries, which is probably related to the fortification of staples, consumption of fatty fish and regular use of vitamin D supplements.
There are several limitations of the present report. The data from vitamin D status was derived from a variety of methods used in the different reports. This measurement is difficult, with large variations between methods and between laboratories using the same methods. In addition, there is lacking representative data from many countries, which precludes the ability to accurately assess vitamin D status from such countries; this is particularly important in countries with different latitudes within its territory.
In conclusion, the available data indicates that vitamin D deficiency is a global public health problem, in all age groups, particularly in those from the Middle East.