Acute effects of oral calcium load on parathyroid function and on bone resorption in young men

AIM: The aim of the present study was to check whether a calcium oral load was able to inhibit bone resorption as assessed by urinary excretion of a new bone marker, type 1 collagen cross-linked C-telopeptide (CrossLaps(TM)), in healthy young male adults. METHODS: Twenty healthy young male adults (age 22 +/- 2 years) were studied. In one series of assays, an oral calcium load of 1 g of elemental calcium as calcium citrate dissolved in 200 ml of low-calcium water was ingested, while in another series of assays the subjects ingested 200 ml of water alone. Blood samples were collected before and 1, 2, 3 and 4 h after the intake of calcium. Urine was collected at 2-hour intervals, i.e. before and for 4 h after the intake of calcium. Serum ionized calcium, phosphate and intact parathormone (iPTH) were measured at each time point. Urinary calcium, phosphate, creatinine and CrossLaps (as a ratio to creatinine) were measured in each urine sample. RESULTS: Calcium intake was associated with very significant (ANOVA, p < 0.001) increases in serum ionized calcium and decreases in PTH. After calcium intake, measurements of urinary CrossLaps showed a progressive statistically significant (ANOVA, p < 0.001) decrease (-20% at 2 h and -55% at 4 h), whereas after ingestion of water, the changes were modest and not statistically significant. CONCLUSIONS: The present results show that bone resorption as assessed by urinary excretion of CrossLaps can be significantly suppressed by the ingestion of a 1-gram calcium load and attest that calcium supplementation has an acute effect on bone metabolism.