Comparative effects of oral aromatic and branched-chain amino acids on urine calcium excretion in humans.
In 30 adults, increasing intake of aromatic amino acids increased calcium excretion and serum IGF-1, but not indices of bone turnover, when compared with similar increases in intake of branched-chain amino acids. The mechanisms involved are not certain but these findings suggest a role for the calcium sensor receptor.


BACKGROUND
In contrast to branched-chain amino acids (BCAAs), aromatic amino acids (AAAs) bind to the calcium sensing receptor (CaR) and thus have an increased potential to affect calcium homeostasis. In this study we compare the effects of increased intake of AAAs versus BCAAs on calcium excretion, serum IGF-1, markers of bone turnover, and 4-hr calcium excretion after an oral calcium load.


METHODS
After two weeks on low-protein metabolic diets, 30 healthy subjects were randomized to a fivefold increase in intake of AAAs or BCAAs for two weeks. Changes in calcium excretion and other measures were compared in the two groups.


RESULTS
With the increase in amino acid intake, 24-hr calcium excretion (P = 0.027), IGF-1 (P = 0.022), and 4-hr calcium excretion after an oral load (P = 0.023) increased significantly in the AAA relative to the BCAA group. Group changes in turnover markers did not differ significantly.


CONCLUSIONS
In comparison with BCAAs, AAAs promoted calcium excretion. The calciuria does not appear to result from increases in bone resorption and may occur by increasing calcium absorption. The AAAs also increased circulating levels of IGF-1. Collectively these findings raise the possibility that AAAs may selectively influence calcium homeostasis through their interactions with the CaR.
Dawson-Hughes
B
B
Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA. bess.dawson-hughes@tufts.edu
Harris
S S
SS
Rasmussen
H M
HM
Dallal
G E
GE
D000284:Administration, Oral; D000368:Aged; D024322:Amino Acids, Aromatic / Q000008:administration & dosage*; D000597:Amino Acids, Branched-Chain / Q000008:administration & dosage*; D015415:Biomarkers / Q000378:metabolism; D001842:Bone and Bones / Q000378:metabolism; D002118:Calcium / Q000652:urine*; D018753:Diet, Protein-Restricted; D005260:Female; D006706:Homeostasis / Q000187:drug effects*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D044169:Receptors, Calcium-Sensing / Q000378:metabolism
D024322:Amino Acids, Aromatic; D000597:Amino Acids, Branched-Chain; D015415:Biomarkers; D044169:Receptors, Calcium-Sensing; D007334:Insulin-Like Growth Factor I; D002118:Calcium