Assessment of solar UV exposure in the Italian population

Solar ultraviolet radiation (UVR) has influenced the evolution of life on earth and likely caused the development of different skin pigmentation in humans: those inhabiting low latitudes, with high UVR intensity, have darker skin pigmentation for protection from the deleterious effects of UVR, while those in higher latitudes have developed fair skin to maximize vitamin D production from much lower ambient UVR. In the last centuries, however, there has been an increase in human migration from its original areas and human skin pigmentation is no longer necessarily suited to the environment where it lives. Dark-skinned populations at low latitudes have very low incidence of melanoma skin cancer (MSC) and non melanoma skin cancer (NMSC, such as squamous cell carcinoma, SCC, and basal cell carcinoma, BCC) but their migration to high latitudes has seen an increase in the incidence of rickets and osteomalacia; meanwhile, fair-skinned populations who have migrated to low latitudes have experienced a rapid rise in the incidence of MSC and NMSC. Furthermore, changes in habits and attitudes have meant that many people all over the globe are now exposed to more, or less, UVR than ever before. In addition, the documented stratospheric ozone downward trend due to chlorofluorocarbons (CFCs) has been associated with an increase of solar ultraviolet radiation B (UVB) at the earth’s surface, even though UVR changes are also associated with fluctuations in cloud cover and atmospheric pollution. If ambient UVR increases, in the absence of changes in personal attitudes and sun protection, there will be an increase in health diseases due to excessive UVR exposure. The only positive human benefit from a moderate degree of solar UVR exposure is the production of vitamin D required for skeletal health. Recently, there has been a debate within the scientific community regarding the health duality of UVR. Various articles have suggested that low vitamin D can be considered a risk factor for breast, prostate and colon cancers. Kimlin’s research group (Australia) is currently focusing on the positive and negative effects of UVR on human health in order to quantify the correct exposure of populations. For such reasons, evaluation of the personal solar UVR doses on different body parts and the search for related easy to measure biological indicators can be helpful in the study of the best levels of exposure and the understanding of what is still unknown. The purpose of this study was to suggest and test a methodology for the measuring of personal solar UVR doses and search for possible biological indicators of its effects. We chose polysulphone (PS) dosimetry as the main investigative methodology. Several field experiments were performed, five of them with groups of volunteers (in vivo) selected among the Italian population (schoolchildren, sun bathers, vineyard growers, skiers and hikers), presented and discussed here. The main result was the data collection of personal UVR exposures, added to the global dataset as Exposure Ratio (ER) between the erythemally weighed dose measured by the PS dosimeter and the corresponding ambient dose on a horizontal plane measured by a radiometer. Mean (median) values of ER on the chest for schoolchildren, sun bathers and hikers were respectively 0.07 (0.07), 0.19 (0.19) and 0.11 (0.07). Since the schoolchildren ER turned out to be the lowest, we asked whether the dose allowed a sufficient production of vitamin D, discovering that some children of the sample showed inadequate modalities of exposure (probably recovered during the summer months). The study on sun bathers, decided so as to supply indications on the relationship between the absorbed doses and the development of the photodermatoses, evidenced that the latter were not linked to high values of Exposure Ratio but they rather depended on the genetic characteristics of the individuals, which probably reacted to the exposure not through the production of melanin but with an increase in the dilation of blood vessels, leading to skin reddening. ER on the forehead for skiers and hikers showed an average value of 1.01 (1.03) and 0.27 (0.24) respectively, with the difference due to snow albedo. The study on vineyard growers, carried out in three different seasons (spring, summer and autumn), supplied an average value of 0.71 (0.69) for the nape and of 0.46 (0.42) for the arm, with an elevated variability due to the different atmospheric conditions and to the different duties between one season and another. The study also proposed a methodology combining the use of colorimetric parameters, skin temperature and additional information (such as the amount of free radicals in the skin) that were collected during the experiments. All data were analyzed by means of well known statistical multivariate approaches, namely PCA (Principal Component Analysis) and Cluster Analysis, useful when variables are not only correlated but also numerous. Finally, to interpret the results, an empirical model for the estimation of short and long term doses was proposed.