Seasonal variation in serum levels of vitamin D metabolites and parathormone in geriatric patients with fractures in Southern Israel.

In 41 geriatric patients with long bone fractures, a seasonal variation was observed in the serum levels of 25-hydroxyvitamin D (25-OH-D), 1,25-dihydroxyvitamin D [1,25(OH)2D], 24,25-dihydroxyvitamin D [24,25(OH)2D] and parathormone (PTH). The serum concentrations of vitamin D metabolites correlate positively, while that of PTH correlates negatively with day length and global solar radiation in southern Israel. Our data suggest that the higher serum levels of vitamin D metabolites during the summer suppress PTH secretion. During the winter, the reduction of serum levels of vitamin D metabolites due to decreased endogenous production was accompanied by an increase in serum PTH levels.