Seasonal changes in calcitropic hormones in Israeli men

Seasonal changes in calcitropic hormones might be expected, being that diet ary calcium intake may differ with fluctuations in climate and temperature, and vitamin D is diet- and sunlight-dependent. While there are studies on elderly subjects, prospective data on younger men is limited. The objective of this study was to clarify possible seasonal changes in homeostatic regu lators of calcium in Israeli men aged 25-64 years. The study was a prospect ive follow-up analysis of data collected during June-August 1995 and 1996 ( summer) and January-March 1995 and 1996 (winter). Subjects were ninety-five industrial male employees with and without occupational lead exposure. The main outcome measures were summer and winter serum concentrations of parat hyroid hormone (PTH), 25-hydroxyvitamin D (25-OH-D), and 1,25-dihydroxyvita min D (calcitriol). Summer and winter values of PTH were similar (38.2 and 39.8 ng/l, respectively). 25-OH-D levels were significantly higher in summe r(32.8 ng/ml) than in winter (25.4 ng/ml) after controlling for possible co nfounders (p < 0.0001). Calcitriol levels were significantly higher in summ er (79.1 pmol/l) than in winter (73.5 pmol/l) in univariate analyses, but n ot after controlling for possible confounders. We conclude that healthy men show considerable seasonal changes in 25-OH-D levels even in Israel, a rel atively sunny country all the year round. Summer values of 25-OH-D, were 35 % higher than in winter. These fluctuations should be taken into account du ring evaluation of pathological conditions and in research. Given an adequa te diet and vitamin D status there are no seasonal variations in PTH or in calcitriol levels.