Submitted to: Osteoporosis International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2006
Publication Date: 7/1/2007
Citation: Dawson-Hughes, B., Harris, S.S., Rasmussen, H.M., Dallal, G.E. 2007. Comparative effects of oral aromatic and branched-chain amino acids on urine calcium and excretion. Osteoporosis International. 18: 955-961. Interpretive Summary: Current evidence suggests that dietary protein may promote calcium absorption but the mechanism for this is not understood. In a recent animal study, the aromatic amino acid component of protein activated calcium sensor receptors (CaRs). CaRs are known to be present on acid producing cells in the stomach and acid secretion promotes calcium absorption. In this study we assessed and compared the effects of aromatic and branched-chain amino acids on calcium absorption and calcium excretion in 30 healthy subjects. The aromatic amino acids significantly increased calcium absorption and excretion. They also increased circulating levels of the bone growth factor, IGF-1. This study supports a role for the CaR in mediating the effect of dietary protein on calcium absorption, calcium excretion, and bone metabolism.
Technical Abstract: Aromatic amino acids (AAAs) bind to the calcium sensor receptor (CaR) but branched-chain amino acids (B-CAAs) do not; by binding to this receptor, AAAs have an increased potential to affect calcium homeostasis. This study was conducted to determine and compare the effects of AAAs and B-CAAs on calcium excretion, calcium absorption, markers of bone turnover, and serum IGF-1. After two weeks on low protein metabolic diets, 30 subjects were randomized to a 5-fold increase in intake of either phenylalanine (phe) and histidine (his) or to leucine (leu) and isoleucine (ileu). Urine calcium, an index of calcium absorption (increase in calcium excretion following an oral calcium load), and serum osteocalcin and urine N-telopeptide (NTX) were measured after two weeks on each diet. Calcium excretion increased by 10.1 +/- 37.3 (SD) mg in the AAA group and decreased by 18.3 +/- 32.4 mg in the B-CAA group, P = 0.034 for difference in change. Calcium absorption index increased significantly with increased intake in the AAA but not the B-CAA group (trend P=0.09 for difference in change). Serum osteocalcin and urinary NTX did not change significantly in either group. On the higher intake, serum IGF-1 increased in the AAA but not in the B-CAA group (P<0.05 for difference in change). In contrast to B-CAAs, AAAs promote calcium excretion. This appears to occur by increasing calcium absorption rather than increased bone resorption. The AAAs also increased circulating levels of IGF-1. The mechanism by which AAAs selectively influence calcium homeostasis is not certain but the above findings suggest a role for the CaR.