The metabolic effects of calcium supplementation in the elderly.

Because the value of calcium supplementation in age-related bone loss is controversial, we conducted a study to examine the effects of six months of calcium supplementation on parathyroid hormone (PTH) and other indices of bone metabolism. Calcium carbonate (1.2 grams elemental calcium/day) or placebo was administered for 6 months to a group of 42 healthy, ambulatory men and women with a mean age of 71. Fasting blood samples and 2-hour urine collections were performed at baseline and at 1 and 6 months. The decline in serum PTH levels from baseline in the calcium-supplemented group was significant in comparison with the placebo group changes (for the calcium group: 40.9 pg/mL at baseline to 34.0 pg/mL at 1 month and 33.2 at 6 months). This drop in PTH was associated with a decline in 1,25 OH-Vitamin D levels from a mean of 38.3 pg/mL to 30.4 pg/mL at 1 month and 31.9 at 6 months. During calcium supplementation, no changes were observed in serum bone Gla protein values. A decline in urinary hydroxyproline excretion was observed at 6 months, but this did not reach significant levels. The present study demonstrates suppression of PTH levels with calcium supplementation, an effect which lasts at least 6 months. This change was accompanied by a decrease in serum 1,25 OH-Vitamin D. The lack of significant changes in either serum bone gla protein or urine hydroxyproline excretion fails to support any significant change in bone turnover occurring with this decrease in PTH.