Estimating the global disease burden due to ultraviolet radiation exposure

Published by Oxford University Press on behalf of the International Epidemiological Association ß The Author 2008; all rights reserved. Advance Access publication 14 February 2008 International Journal of Epidemiology 2008;37:654–667 doi:10.1093/ije/dyn017 Estimating the global disease burden due to ultraviolet radiation exposure Robyn M Lucas,1* Anthony J McMichael,1 Bruce K Armstrong2 and Wayne T Smith3 Accepted 14 January 2008 Methods A systematic literature review identified nine diseases with sufficient evidence of a causal relationship with UVR exposure and for which the population attributable fraction (PAF) for UVR could be estimated. For cutaneous malignant melanoma and cataract, the PAF was directly applied to disease burdens already calculated by WHO. For seven other diseases, we developed population-level exposure–disease relationships and used these to calculate disease incidence and mortality, and thence disease burden. We also estimated the disease burden from rickets, osteomalacia and osteoporosis that might result if global UVR exposure was reduced to very low levels. Results UVR exposure is a minor contributor to the world’s disease burden, causing an estimated annual loss of 1.6 million DALYs; i.e. 0.1% of the total global disease burden. A markedly larger annual disease burden, 3.3 billion DALYs, might result from reduction in global UVR exposure to very low levels. Conclusions Sun protection messages are important to prevent diseases of UVR exposure. However, without high dietary (or supplemental) intake of vitamin D, some sun exposure is essential to avoid diseases of vitamin D insufficiency. Keywords Ultraviolet rays, risk assessment, vitamin D, skin cancer, eye diseases, world health, environmental exposures 1 National Centre for Epidemiology and Population Health, The Australian National University, Australia. 2 Sydney Cancer Centre, Royal Prince Alfred Hospital, and School of Public Health, The University of Sydney, Australia. 3 Centre for Clinical Epidemiology and Biostatistics, Newcastle University, Australia. * Corresponding author. National Centre for Epidemiology and Population Health, Building 62, The Australian National University, Canberra ACT 0200, Australia. E-mail: Background Optimizing sun exposure for good health is currently the subject of considerable controversy. Past research has focused on understanding the adverse health effects of sun exposure, especially in relation to risks of skin cancer and the recent additional threat from stratospheric ozone depletion. Meanwhile, many diseases have now been linked, albeit some rather tenuously, with vitamin D deficiency—such that the protective effect of sun exposure might offset, 654 Background WHO’s global burden of disease studies, undertaken since 1996, apportion the total global disease burden, measured in disabilityadjusted life years (DALYs), to specific diseases and injuries. Recent assessments of the relative burden due to specific environmental risk factors, plus an understanding of the nature of the risk factor, may guide resource allocation in risk factor management. We report here the global disease burden due to ultraviolet radiation (UVR) exposure. UV RADIATION EXPOSURE AND GLOBAL DISEASE BURDEN Exposure to ultraviolet radiation: a health hazard? Living organisms on Earth evolved over many hundreds of millions of years under selection pressures that included differing levels of UVR. Skin pigmentation may have evolved under the competing pressures of protection of underlying cell structures from radiation damage and maximization of vitamin D production,8 critical for bone health. Solar UVR is ubiquitous during daylight hours. Ambient ground-level UVR comprises mainly UVA (400—315 nm) plus a small proportion (<10%, variable by time of day, season and location) of UVB (315–280 nm). Within-person and between-person UVR doses vary greatly, depending on location, time of day and season, clothing habits and behaviour and skin pigmentation. Notably, UVR is one of few environmental exposures that may both cause and protect against disease: protecting against diseases of vitamin D insufficiency and causing skin cancers and eye diseases. Methods A systematic review of the epidemiological literature identified nine diseases showing sufficient evidence of a causal association with UVR exposure (as judged by the Bradford Hill ‘criteria’).9 Diseases of sporadic occurrence (e.g. photokeratitis and photoconjunctivitis, solar retinopathy) and the photodermatoses, which were considered to be caused by enhanced individual susceptibility rather than by over- or under-exposure, were excluded from the assessment. A further three diseases were causally associated with insufficient UVR exposure, via vitamin D deficiency (Table 1). For each included disease the population attributable fraction (PAF)10 for UVR was calculated from published epidemiological literature [The PAF is that fraction of disease incidence that is attributable to exposure to the risk factor (and thus the fraction by which incidence could be reduced by elimination of exposure to that risk factor)]. Given the variations in published risk and exposure data, we estimated the upper and lower values of disease-specific PAF or, in one case, relied on a single ‘best estimate’ (Table 2). The UVR-attributable disease burdens were then calculated by applying the PAF to the estimated total burdens.6,11 For cutaneous malignant melanoma (CMM) and cortical cataract the estimated PAFs were directly applied to the disease burden calculated in the GBD 2000. For other diseases, the disease-specific burden was calculated (in DALYs) from available evidence on the duration and disability weight (DW) for each disease stage and disease-specific incidence and mortality, as described below. Disease models were developed from available literature and by consultation with clinical experts, providing estimates of the proportions of incident or prevalent cases progressing through, and the duration of, each disease stage (Figure 1). DWs for each disease stage were derived from the GBD studies and Dutch12 and Australian studies.13 Non-melanoma skin cancers: squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) Few population-based disease registries record these skin cancers, and therefore accurate global incidence and mortality statistics are not available. Age-group and sex-specific incidence rates of SCC and BCC were derived from published populationbased incidence studies and plotted against average daily ambient erythemal UVR (from satellite monitoring data)14 for each study location and study year(s), e.g. Figure 2. The average daily ambient UVR for each country for the year 2000, weighted according to the within-country distribution of the population, was calculated by overlaying daily ambient erythemal UVR, estimated from satellite data14 and averaged over 1997–2003, with the gridded world population, multiplyi (...truncated)