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.

• poly-γ-glutamic acid
• natto
• fermented soybeans
• stable isotopes
• calcium absorption
• post-menopausal women

This study was funded by the Ajinomoto Company, Japan. The authors thank Rob Foxall, Institute of Food Research, Norwich, UK, for statistical support. The authors thank Dr. David P. Katz, Consultant to Ajinomoto USA, for his review and suggestions for the paper.