Biologically efficient solar radiation: Vitamin D production and induction of cutaneous malignant melanoma

Abstract

Solar ultraviolet (UV) radiation is the main source of vitamin D production and is also the most important environmental risk factor for cutaneous malignant melanoma (CMM) development. In the present study the relationships between daily or seasonal UV radiation doses and vitamin D status, dietary vitamin D intake and CMM incidence rates at different geographical latitudes were investigated. North-South gradients of 25-hydroxyvitamin D (25(OH)D) generation and CMM induction were calculated, based on known action spectra, and compared with measured vitamin D levels and incidence rates of CMM. The relative roles of UVA and UVB in CMM induction are discussed. Latitudinal dependencies of serum 25(OH)D levels and CMM incidence rates can only partly be explained by ambient UV doses. The UV sensitivity is different among populations with different skin color. This is well known for CMM, but seems also to be true for vitamin D status. The fact that UV-induced vitamin D may reduce the risk of CMM complicates the discussion. To some extent high dietary vitamin D intake seems to compensate low UV doses.

Keywords: UVA and UVB ratio; cutaneous malignant melanoma; photoimmunosuppression; solar ultraviolet radiation; vitamin D.

Figure 1. UV doses per day at different latitudes on the northern hemisphere for erythema induction (A), vitamin D production (B) and induction of immunosuppression (C).

Figure 2. UVA and UVB intensities (normalized to the same value at the Equator) before and after penetration of epidermis in Oslo (A) and in the Equator (B).

Figure 3. Latitudinal dependency of annual UV doses on the northern hemisphere for immunosuppression, erythema and DNA damage.

Figure 4. The age-standardized incidence rates (ASIR) according to the world standard population (W) per 100,000 males (A) and females (B) for CMM in different countries.

Figure 5. Summer and winter levels of 25(OH)D and dietary intake of vitamin D in populations living at different latitudes (A). Theoretically estimated relative summer to winter ratios of vitamin D photosynthesis (according to the effective UV doses, Fig. 1B) and the summer to winter ratios of measured 25(OH) D levels (B). 25(OH) D levels are taken from panel (A).