UV-exposition is considered as the main reason for the development of cancers of the skin. However, 90 to 100% of the Vitamin-D reqirement is formed within the skin through the action of sunlight. Considering the results of epidemiological studies, that have detected an association of Vitamin-D deficiency with various types of cancer (e.g. colon-, prostate-and breast cancer), this is a real dilema. The cancer protective effect of vitamin-D is contributed to the extra renal, local production of 1a,25(OH) 2 D 3 by the 25-hydroxyvitamin D-1a-hydroxylase, which has been detected in various tissues. In respect of the novel functions of vitamin-D and the risk of adverse consequences in case of deficiency we have screened sun deprived risk groups (A: patients with genodermatoses connected with defects in sun-induced DNA repair: n ¼ 4: 3 patients with xeroderma pigmentosum and 1 patient with basal cell nevus syndrome; and B: non vitamin-D substituted renal transplant recipients under immunosuppressants: n ¼ 33) for their vitamin-D status. As measure of the vitamin-D store and as substrate for the 25-hydroxyvitamin D-1a-hydroxylase basal 25(OH)D 3 serum levels (Nichols Institute Diagnostika GmbH, Bad Nauheim, Germany) have been analysed. In both groups decreased basal 25(OH)D 3 serum levels were detected. Therefore we demand a monitoring of vitamin-D status in patients practising sun protection, in case of vitamin-D deficiency an oral substitution should be recommended.Effect of UVB radiation emitted from the narrowband TL-01 lamp (311 nm) on the calcitriol synthesis in organotypic cultures of keratinocytesThe skin is the only tissue yet known in which the complete UVB-induced pathway from 7-dehydrocholesterol (7-DHC) to hormonally active calcitriol (1a,25-dihydroxyvitamin D 3 ) occurs under physiological conditions. It is well known that both calcitriol and UVB radiation exert potent antipsoriatic effects. We speculate that the therapeutic effect of UVB radiation can be
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