EFFECTS OF AGE, SEX, SEASON AND DIET ON SERUM IONIZED CALCIUM, PARATHYROID-HORMONE AND VITAMIN-D IN A RANDOM-POPULATION

Objectives. To study the influence of age, sex, season and diet on calcium status in normal subjects. Design. A random population study. Setting. Institutional clinic for large population studies. Subjects. The subjects were drawn randomly from the Danish Civil Registration System and represented a random sample of the background population in the area. The sample comprised 127 subjects (54 men and 73 women, aged 35-65 years). Main outcome measures. The effects of age, sex, season and diet on parathyroid hormone (PTH),1,25-dihydroxyvitamin D (1,25(OH)2D) and 25-hydroxyvitamin D (25-OHD). Results. There was no statistical significant difference for the serum concentrations of ionized calcium, PTH, 1,25(OH)2D and 25-OHD between the two sexes, nor any influence by age in either sex, in contrast to serum phosphate, which declined significantly in men (P < 0.05), but tended to increase in women. Serum PTH (P < 0.009) showed seasonal fluctuations, whereas serum concentrations of 1,25(OH)2D, 25-OHD, ionized calcium, phosphate and magnesium remained stable throughout the year. Dietary intake of calcium and vitamin D were not related to any serum variables. Conclusions. In healthy subjects differences between the two sexes exist regarding phosphate metabolism. Serum PTH shows seasonal fluctuations.