ACUTE ORAL CALCIUM-SODIUM CITRATE LOAD IN HEALTHY-MALES - EFFECTS ON ACID-BASE AND MINERAL METABOLISM, OXALATE AND OTHER RISK-FACTORS OF STONE FORMATION IN URINE

The currently preferred calcium preparations for supplementation of fo od vary widely with respect to calcium availability effects on systemi c mineral metabolism, acid-base status, and the calciuria-induced risk of urinary tract stone formation. In eight healthy males we studied t he response to an acute load with alkali(sodium)-containing soluble ca lcium citrate (CSC) (molar ratio calcium/sodium/citrate approx. = 1/1/ 1), when taken in three different doses (10, 20, 30 mmol calcium) toge ther with a continental breakfast. Intestinal calcium absorption, seru m calcium, calcitonin, parathyroid hormone (PTH) other markers of bone metabolism, net acid excretion and calcium oxalate crystallization in urine were evaluated CSC evoked a dose-dependent increase in calcium absorption, calcium in serum and urine, but no overt hypercalcemia and calciuria was low relative to the excess calcium ingested; PTH fell a nd calcitonin rose (p < 0.05 vs. breakfast alone), but the diet-indepe ndent markers of bone resorption declined only insignificantly while t he markers of bone formation and turnover remained unchanged. There wa s a significant ''once-daily'' effect (= cumulative 24 h postload resp onse) of CSC: a decrease in urinary cyclic AMP: phosphorus, and ammoni um, and art increase in urinary bicarbonate. Soon after CSC intake, ur inary calcium oxalate and hydroxyapatite supersaturation increased dos e-dependently, the calcium oxalate crystal diameter was increased but crystal aggregation time, which is crucial for stone formation, remain ed statistically unchanged. Thus, CSC provides calcium in a bioavailab le form, creates mild systemic alkalinisation and inhibition of bone r esorption, but leaves the risk of developing urinary stones unchanged. Comparative long-term studies on bone growth and the maintenance of b one health, using alkali-containing versus alkali-free calcium citrate , appear worthwhile.