The climatology of Vitamin D producing ultraviolet radiation over the United States

The US population is located in a wide range of latitudes, longitudes, and altitudes over mainland United States. Subsequently, high UV irradiants are found at southern locales, whilst in some northern areas, particularly at high latitudes, insufficient levels of ambient UV radiation to synthesize pre Vitamin D in humans are reported. This fact, coupled with the cold northern climates (resulting in high amounts of skin covered in clothing), some people may be susceptible to hypovitaminosis D. Surprisingly, hypovitaminosis D is still relatively common in developed countries such as the USA and the UK. In a large epidemiologically based study of 15,778 noninstitutionalized adult men and women living in the US, 9% had low serum 25-hydroxyvitamin D levels (15 ng/ml) [N. Engl. J. Med. 339 (1998) 12]. Further evidence of this came from recent research by McGrath [Med. Hypertens. 56 (2001) 367] who found that adults living in South East Queensland (with Queensland known as having the highest rates of skin cancer in the world) have surprisingly high rates of Vitamin D deficiency and insufficiency (8 and 23%, respectively). Therefore, hypovitaminosis D represents a serious issue for public health in both sunny and cold climates. This paper will present data on the distribution of Vitamin D forming UV over the USA using collected spectrally resolved ambient UV data from the US EPA Brewer spectrometer UV Monitoring Network. This data is obtained from the network of 21 Brewer spectrometers deployed throughout the USA, allowing for investigation of changes in Vitamin D producing UV with season and location.