Is Multidirectional UV Exposure Responsible for Increasing Melanoma Prevalence with Altitude? A Hypothesis Based on Calculations with a 3D-Human Exposure Model

Abstract

In a recent study, melanoma incidence rates for Austrian inhabitants living at higher altitudes were found to increase by as much as 30% per 100 m altitude. This strong increase cannot simply be explained by the known increase of erythemally-weighted irradiance with altitude, which ranges between 0.5% and 4% per 100 m. We assume that the discrepancy is partially explainable by upwelling UV radiation; e.g., reflected by snow-covered surfaces. Therefore, we present an approach where the human UV exposure is derived by integrating incident radiation over the 3D geometry of a human body, which enables us to take upwelling radiation into account. Calculating upwelling and downwelling radiance with a radiative transfer model for a snow-free valley and for snow-covered mountain terrain (with albedo of 0.6) yields an increase in UV exposure by 10% per 100 m altitude. The results imply that upwelling radiation plays a significant role in the increase of melanoma incidence with altitude.

UV “Indices”—What Do They Indicate?

“…We found a positive and significant association between exposure and melanoma incidence. Schrempf et al in this issue [2] correctly point out that the increase in melanoma incidence per 100 m in altitude is much larger than the increase in UV exposure for the same difference in altitude as assessed in our paper. We did not see the same association of altitude or UV exposure with melanoma mortality, and there is some indication that melanoma reporting differs between federal countries in Austria, with more complete reporting also by general practitioners in the more mountainous areas of the provinces of Carinthia and Tyrol.…”

“…Therefore, the exposure data recorded by a spectrometer also strongly depend on the orientation of its measurement surface. There is no way to ensure that it captures all possible orientations of all surfaces of the human skin [2]. …”

“…So why did Schrempf et al [2] conclude that our exposure estimates were rather biased? We used a weighted metric of UV radiation measured on a horizontal detector.…”

Ozone—climate interactions and effects on solar ultraviolet radiation

“…213 For example, the exposure of the human body to UV radiation was calculated with a radiative transfer model by integrating incident radiation over the 3D geometry of the body. 214 When this approach is applied for a snow-free valley and for snow-covered mountain terrain (with albedo of 0.6), an increase in UV exposure by 10% per 100 m increase in altitude was found, which is more than 10 times larger than the usual increase in erythemally weighted UV irradi-ance with altitude in snow-free conditions. 2,92 The results imply that upwelling radiation is an important source of exposure to UV radiation affecting human health where exposure occurs at higher altitudes.…”

Combining population projections with quasi-likelihood models: A new way to predict cancer incidence and cancer mortality in Austria up to 2030

“…The observed diverging incidence and mortality trends might be explained by diagnosis at earlier tumor stages due to better screening adoption in these regions and vitamin D-driven slower tumor progression (Monshi et al 2016). Also, upwelling radiation caused by, e.g., sunlight reflected by snow cover, could also explain higher melanoma incidence rates with altitude (Schrempf et al 2016).…”