The vitamin D status of man at 70 degrees north.

The overall vitamin D status of man at 70 degrees north has been evaluated by measuring the total 25-hydroxy-vitamin D (25-OHD) in serum samples from seventeen healthy adults from September 1977 to September 1978. The lowest 25-OHD-concentration was found in March (mean 51.5 nmol/l, SD = 19.5). This was significantly lower than in July and September 1977 and 1978 (P less than or equal to 0.0006). Of particular interest was the highly significant rise in the 25-OHD-concentration from March to July, most probably reflecting sun-induced endogenous synthesis in the skin. Despite the sun being below the horizon for two of the winter months, the 25-OHD-concentration remained at a constant and fairly high level (50-55 nmol/l).