Time trend of UVB irradiation and the vitamin D concentration in German type 1 diabetes patients

Background: Type 1 diabetes (T1D) is an autoimmune disease which is characterised by the destruction of insulin-producing beta cells in human pancreas leading consequently to a hyperglycaemic metabolism. Recent studies have shown that low cholecalciferol (25(OH)D-3) concentrations may contribute to the development of T1D. The 25(OH)D-3 status depends mostly on human skin production influenced by exposure to UVB radiation. Our intention was to examine whether there was a change in UVB radiation in the past years and if this has an impact on patients' vitamin D status. Methods: We analysed the 25(OH)D-3 concentration of blood samples from 287 T1D patients in the years 2004-2007 at the University Hospital Frankfurt. Moreover, daily UVB irradiation data of this time were received. Wilcoxon-Mann-Whitney test and Spearman correlation test were used for statistical analyses. Results: We observe a strong correlation between UVB irradiation and the 25(OH)D-3 concentration of German T1D patients (correlation coefficient = rho = 0.56, p = 7 x 10(-3)). Moreover, 25(OH)D-3 blood levels obtained in summer (Apr-Oct) were significantly higher than in the winter season (p = 8 x 10(-3)). In the years 2004-2007 there was a significant decline of UVB radiation in the summers (rho = -0.21, p < 10(-6)) but no change was found in (rho = -0.07, p = 0.12). This corresponds to a significant decrease of 25(OH)D-3 levels in T1D patients over the summers (rho = -0.24, p = 2 x 10(-3)) but not in winters (rho = -0.03, p = 0.73). Conclusion: Our results reveal a significant correlation of UVB irradiation and the vitamin D concentration of German T1D patients. A decrease of UVB irradiation over the summers 2004-2007 is accompanied by a decline of 25(OH)D-3 levels observed in those summer months which may indicate a local time trend requiring further investigation into the environmental factors of vitamin D deficiency. This article is part of a Special Issue entitled 'Vitamin D Workshop'. (C) 2012 Elsevier Ltd. All rights reserved.