Calcitriol corrects deficient calcitonin secretion in the vitamin D-deficient elderly

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Abstract
The thyroid calcitonin‐producing C cells possess vitamin D receptors and synthesize the vitamin D‐dependent calbindin D28K. The present study evaluates the possible direct or indirect influence of vitamin D on calcitonin secretion in the elderly. Serum calcitonin was measured before 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 elderly subjects (78 ± 4 years). The test was repeated 48 h after the last of three intravenous injections of calcitriol (2 μg) 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), similar to basal values in young adults (11 ± 1 pg/ml). The increase in calcitonin 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 calcitriol 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 parathyroid hormone.