Acute Effect of Poly-γ-Glutamic Acid on Calcium Absorption in Post-Menopausal Women

Abstract

Objective: Poly-γ-glutamic acid (PGA) increases calcium (Ca) solubility in vitro and in vivo, and is associated with reduced bone loss in post-menopausal Japanese women. This study is the first to examine the effect of PGA on Ca absorption in humans.Methods: A single-blind, randomized, crossover study with a 3–4 week wash-out was performed to determine the effect of PGA (80.6% glutamic acids) on Ca absorption measured by the double stable isotope method. Twenty-four healthy, non-smoking, postmenopausal women (mean age: 56.4 ± SE 0.9) were given 200 g of orange juice containing 200 mg Ca as Ca-44 enriched CaCO3, with or without 60 mg of PGA, after an overnight fast. The two tests were separated by 3–4 weeks. An intravenous injection of Ca-42 (CaCl2 solution) was given 30 min after consuming the drink and a complete urine collection carried out from 24–48 h post-dosing. Ca absorption was calculated from the Ca isotope ratios measured by thermal ionization quadrupole mass spectrometry (TIQMS).Results: Mean Ca absorption with PGA was significantly higher (P < 0.01) than without PGA, 39.1 (SE 1.6) % and 34.6 (SE 1.9) %, respectively. The effect of PGA on increasing Ca absorption was more marked in a sub-group of subjects whose baseline Ca absorption (without PGA) was lower than the population mean value.Conclusion: Postmenopausal women who received a single dose of PGA increased their intestinal Ca absorption particularly those individuals with lower basal absorptive capacity.