Vitamin D metabolism in polar vertebrates

1. Studies of serum 25-hydroxy-vitamin D (25-OHD) in the Antarctic have been undertaken in husky dog, seal and penguin and compared to man. 2. Husky dogs showed a reversal of the expected seasonal variation of serum 25-OHD with maxima in June when the hours of bright sunshine and amount of u.v.-B radiation were lowest. li3. Values for random serum 25-OHD values in seals showed large interspecies differences, the values for Weddell seals being significantly greater than for Crabeater seals (P < 0.01). 3. Penguin sera showed low concentrations of serum 25-OHD with no evidence of a response to prolonged exposure to sunlight.