EFFECT OF SEASONAL ULTRAVIOLET-RADIATION FLUCTUATIONS ON VITAMIN-D HOMEOSTASIS DURING AN ANTARCTIC EXPEDITION

Antarctica is a unique and challenging environment where members of ex peditions face a range of conditions not normally experienced. Ultravi olet (uv) radiation levels show marked variation during the year. The 25-hydroxy metabolite of vitamin D [25(OH)D] is largely produced by su nlight and shows a yearly variation in concentration that corresponds to uv radiation levels. The active metabolite 1,25-dihydroxyvitamin D [1,25(OH)2D] does not generally show any such variation provided 25(OH )D concentrations are sufficient. Previous studies have shown a season al variation in 25(OH)D with a significant winter drop. No other study of 1,25(OH)2D has been reported on members of Antarctic expeditions. A group of 19 men wintering at Davis Station (68 degrees 34' S) had fo ur blood samples taken at 3-monthly intervals beginning in the Antarct ic summer. Analysis for 25(OH)D showed a drop in concentration for eac h of the latter three sampling periods (P<0.005). This correlated with uv radiation levels and would suggest that endogenous production of 2 5(OH)D ceases for at least the duration of the Antarctic winter. There were no significant alterations in 1,25(OH)2D or calcium concentratio ns over the same period. Providing that individuals with pre-existing vitamin D deficiencies are detected before departure for Antarctica an d missions are limited in duration, clinical deficiency is unlikely to occur.