AGE-RELATED EFFECT OF A SINGLE ORAL DOSE OF CALCIUM ON PARATHYROID FUNCTION - RELATIONSHIP WITH VITAMIN-D STATUS

The parathyroid response to the administration of a single oral dose o f 0.5 g Cal was studied in 71 normal subjects of both sexes (34 males, 37 females) aged 20-88 y. Serum 25-hydroxyvitamin D [25(OH)D] and 1,2 5-dihydroxyvitamin D [1,25(OH),D] were measured before the intake of c alcium. Serum ionized calcium (Ca++) and intact parathormone (PTH1-84) were measured before and 1, 2, and 3 h after the intake of calcium. T he Ca++ maximal response (Delta Ca-max(++)), which significantly decre ased with age (P = 0.0001), was correlated with both 25(OH)D (r = 0.37 5, P < 0.01) and 1,25(OH)1D (r = 0.284, P < 0.02). The maximal PTH1-84 suppressive response expressed as a function of basal values (Delta P TH%) decreased with age. Basal PTH1-84 values were significantly incre ased with age (P = 0.0002) and were negatively correlated with 25(OH)D concentrations (r = 0.414, P < 0.002) which were low in elderly peopl e. These results suggest that correction of vitamin D deficiency shoul d improve Delta Ca-max(++), lower basal PTH1-84, and consequently make the oral intake of calcium more efficient to decrease PTH1-84 concent rations.