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 of 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 1,25-dihydroxyvitamin D [1,25(OH)2D] were measured before the intake of calcium. Serum ionized calcium (Ca++) and intact parathormone (PTH1-84) were measured before and 1, 2, and 3 h after the intake of calcium. The Ca++ maximal response (delta Ca++max), which significantly decreased with age (P = 0.0001), was correlated with both 25(OH)D (r = 0.375, P < 0.01) and 1,25(OH)2D (r = 0.284, P < 0.02). The maximal PTH1-84 suppressive response expressed as a function of basal values (delta PTH%) decreased with age. Basal PTH1-84 values were significantly increased 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 people. These results suggest that correction of vitamin D deficiency should improve delta Ca++max, lower basal PTH1-84, and consequently make the oral intake of calcium more efficient to decrease PTH1-84 concentrations.