CALCITRIOL CORRECTS DEFICIENT CALCITONIN SECRETION IN THE VITAMIN-D-DEFICIENT ELDERLY

The thyroid calcitonin-producing C cells possess vitamin D receptors a nd synthesize the vitamin D-dependent calbindin D-28K The present stud y evaluates the possible direct or indirect influence of vitamin D on calcitonin secretion in the elderly. Serum calcitonin was measured bef ore and after a short calcium infusion (1.5 mg/kg over 10 minutes) in nine normal young adults (30 +/- 4 years, mean +/- SEM) and eight elde rly subjects (78 +/- 4 years). The test was repeated 48 h after the la st of three intravenous injections of calcitriol (2 mu g) given every other day. Basal serum calcium did not change, but basal calcitonin of the elderly increased from 7 +/- 1 to 10 +/- 1 pg/ml(p < 0.06), simil ar to basal values in young adults(11 +/- 1 pg/ml). The increase in ca lcitonin after calcium infusion increased from 8 +/- 1 to 14 +/- 1 pg/ ml (p < 0.001) after calcitriol treatment and approached the increase in young adults (18 +/- 3 pg/ml). These data demonstrate that calcitri ol can improve and nearly normalize the impaired calcitonin secretion of the mildly vitamin D-deficient elderly subjects without changes in serum calcium, whereas the inverse situation is observed for parathyro id hormone.