The influence of oral alkali citrate on intestinal calcium absorption in healthy man

Abstract

The influence of citrate on intestinal calcium absorption (CaA) was studied in eight healthy males. On separate occasions, either a load containing 5 mmol of calcium chloride and 21 mmol of citrate in the form of sodium potassium citrate or a citrate-free vehicle load corrected for pH and cations was ingested. CaA was measured over 3 h with a 47Ca-85Sr double tracer method. After citrate administration, 10 min fractional CaA decreased significantly from 30 to 110 min post-load, and 3 h cumulative CaA dropped to 54.6 +/- (SEM) 6.1% of the total dose as opposed to 76.3 +/- 4.5% after vehicle administration (P less than 0.002). Citrate administration raised serum and urinary citrate, but had little effect on blood acid-base status. After both loads, urinary specific activity of 47Ca significantly correlated with 3 h cumulative CaA, while citrate administration decreased urinary calcium excretion only slightly as compared with vehicle. The results suggest that, in man, higher doses of oral citrate inhibit CaA, probably by way of intraluminal complexation of calcium by citrate. The finding might help explain the fall in urinary calcium excretion observed in patients treated with alkali citrate for recurrent calcium urolithiasis.

ICRP Publication 134: Occupational Intakes of Radionuclides: Part 2

“…However, unlike strontium, barium, and radium, the other alkaline earth elements, calcium is an essential element and physiological mechanisms facilitate its intestinal absorption. (226) Calcium absorption has been measured in numerous volunteer studies, and the reported mean absorption values were in the range 0.2–0.5 in most cases (Samachson, 1963; DeGrazia and Rich, 1964; Lutwak, 1969; Mautalen et al., 1969; Jovanovic, 1978; Cochet et al., 1983; Marchandise et al., 1986; Spencer et al., 1987; Harvey et al., 1988; Heaney et al., 1989, 1999). Greater mean values of 0.6 (Sambrook et al., 1985) and 0.7 (Rumenapf and Schwille, 1987) have also been reported for normal volunteers. These differences may probably be explained by the large interindividual differences in calcium absorption observed in healthy subjects, with individual values ranging from 0.3 to 0.6 (Barger-Lux and Heaney, 1995) or even from 0.4 to 0.9 (Isaksson et al., 2000).…”

“…These differences may probably be explained by the large interindividual differences in calcium absorption observed in healthy subjects, with individual values ranging from 0.3 to 0.6 (Barger-Lux and Heaney, 1995) or even from 0.4 to 0.9 (Isaksson et al., 2000). Indeed, calcium absorption depends first on the intraluminal concentration of ionised calcium (Schachter et al., 1960), which can be reduced locally by the presence of calcium binding agents such as EDTA or citrate ions (Rumenapf and Schwille, 1987). Additional variability may be associated with morphological factors as calcium absorption is positively correlated with body size (Davies et al., 2000; Barger-Lux and Heaney, 2005) and many nutritional factors.…”

Effects of magnesium citrate and phytin on reducing urinary calcium excretion in rats

“…Another hypocalciuric effect of magnesium citrate may be attributable to the observation that citrate combines with dietary calcium in the intestine to form the nondissociating, readily dissolving, and poorly absorbable calcium-citrate chelate complex [ 17,18]:…”

The Effects of Acid on Calcium and Phosphate Metabolism

“…Other studies, however, have not found suppression of 1,25(OH) 2 D 3 production in normal adults [25], nor a reduction in the intestinal absorption of calcium or phosphorus after the induction of metabolic acidosis [26]. There are reports of either increased [27,28] or decreased [29] intestinal calcium absorption after alkali administration.…”