Calcium supplementation lowers serum parathyroid hormone levels in elderly subjects

To determine the effect of calcium supplementation on parathyroid hormone levels (PTH) in a group of elderly subjects at risk for developing Type II (senile) osteoporosis, 40 healthy volunteers participated in a randomized double-blind crossover study. Calcium carbonate or placebo was administered for 4 weeks, followed by a 4-week administration of the alternative intervention. Fasting blood samples and 24-hour urine collections were obtained at baseline, and at the end of each intervention period. Calcium supplementation (1000 mg/day) decreased serum PTH levels from a mean of 50.1 +/- 3.0 pg/ml to 41.9 +/- 2.4 pg/ml (p less than .001). Additionally, urine calcium excretion significantly increased during calcium administration (from 3.64 mmol/mmol creatinine at baseline to 4.28 mmol/mmol creatinine), but creatinine clearances and serum calcium levels remained unchanged. Type II osteoporosis has been associated with age-related increases in PTH levels. We have demonstrated the ability of increased calcium intake to decrease these levels, which may have implications for the management of a subset of patients with involutional osteoporosis.