Although most ultraviolet B (UVB) radiation is absorbed by stratospheric ozone, dense anthropogenic sulfate aerosols in the troposphere may further attenuate UVB in some regions. Mortality rates from colon and breast cancer tend to be much higher in areas with low levels of UVB radiation. These high rates may be due in part to inadequate cutaneous photosynthesis of vitamin D. Satellite data on atmospheric aerosols, stratospheric ozone, and cloud cover were obtained from the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA). These data were combined with age-adjusted mortality rates from 175 countries reporting to the World Health Organization. Regression was used to assess the relationship of stratospheric ozone thickness, aerosol optical depth, cloud cover, solar UVB irradiance at the top of the atmosphere, average skin exposure, and a dietary factor with colon and breast cancer mortality rates. Solar UVB irradiance at the top of the atmosphere, total cloud cover, and atmospheric aerosols had the strongest associations with mortality rates, apart from a strong influence of diet. Since 95% of circulating vitamin D is derived from current or stored products of photosynthesis, which may be nonexistent or minimal much of the year above 37°N or below 37°S, attenuation of UVB by atmospheric aerosols and clouds may have a greater than expected adverse effect on human health.
Moderate exposure to sunlight is a key factor in maintaining adequate levels of vitamin D. Vitamin D sufficiency is associated with reduced incidence of many forms of cancer, osteoporotic fractures, multiple sclerosis, and other diseases. However, excessive ultraviolet radiation (UVR) exposure may be associated with melanoma and nonmelanoma skin cancer. An estimated 50,000-60,000 individuals die prematurely from cancer annually due to insufficient vitamin D in the US. The annual economic burden due to vitamin D insufficiency from inadequate exposure to solar ultraviolet B (UVB) or deficient oral intake is estimated at $46-65 billion, while that for excessive UVR exposure is $5-7 billion (1). Since excessive UVR exposure is not required for adequate vitamin D photosynthesis, increasing national guidelines for vitamin D intake and de-stigmatizing appropriate solar UVB exposure would substantially reduce medical care costs. This report describes an algorithm for estimating the annual number of dollars that could be saved and deaths from colorectal cancer that could be prevented by moderate daily exposure to sunlight or increased oral intake of vitamin D<sub>3</sub>. If the assumptions of this analysis are valid, moderate exposure to sunlight or adequate oral intake of vitamin D<sub>3</sub> would prevent 10 deaths from colorectal cancer for every death from skin cancer that it might induce, and would save $11 billion per year. Reference: (1) Grant WB, Garland CF, Holick MF. Comparisons of estimated economic burdens due to insufficient solar ultraviolet (UV) irradiation or vitamin D and excess solar UV irradiation. <i>Photochem Photobiol</i>. In press.
Background: Recent advances confirming the role of vitamin D in prevention of cancer have created new scientific interest. The main source of vitamin D is exposure to ultraviolet B (UVB). Factors that reduce atmospheric penetration of UVB play a role in increasing risk of cancers of the colon, breast, and other sites. Objective: To systematically review available epidemiological and laboratory studies concerning effects of UVB or vitamin D on colon, breast, prostate and ovarian cancer. Methods: All published research articles that identified the role of ultraviolet B, vitamin D, and its metabolites in conjunction with colon and breast cancer were ascertained and abstracts or articles were reviewed. Results: The preponderance of epidemiological and laboratory studies support the hypothesis that moderate exposures to ultraviolet B and vitamin D provide protection against colon and breast cancer, among others. The effect is present throughout life for colon cancer, but is exerted mostly during the first two decades for breast cancer. Conclusion: Latitude, climate, sulfate air pollution, stratospheric ozone, and behavioral factors combine to reduce the dermal synthesis of vitamin D to virtually zero during winter months. Populations at 37+ degrees of latitude are at markedly elevated risk of vitamin D deficiency, and, consequently, of colon, breast and prostate cancer incidence and mortality.