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Journal of the American College of Nutrition, Vol. 26, No. 6, 645-649 (2007)
Published by the American College of Nutrition

Acute Effect of Poly-{gamma}-Glutamic Acid on Calcium Absorption in Post-Menopausal Women

Hiroyuki Tanimoto, MSc, Tom Fox, PhD, John Eagles, LRSC, Hitoshi Satoh, MSc, Hiroko Nozawa, BSc, Atsushi Okiyama, PhD, Yasushi Morinaga, PhD and Susan J. Fairweather-Tait, DSc

Institute of Food Research, Norwich Research Park, Colney (H.T., T.F., J.E.)
Diet and Health Group, School of Medicine, Health Policy and Practice, University of East Anglia (S.J.F.-T.)
Norwich Norfolk, UNITED KINGDOM, Food Research & Development Laboratories, Ajinomoto Co., Inc., Kawasaki-ku, Kawasaki, JAPAN (H.T., H.S., H.N., A.O., Y.M.)

Address reprint requests to: Hiroyuki Tanimoto, Health Foods Business Group, Seasonings Dept., Ajinomoto Co., Inc., 15-1, Kyobashi 1-Chome, Chuo-ku, TOKYO 104-8315, JAPAN. E-mail: hiroyuki_tanimoto{at}ajinomoto.com

Objective: Poly-{gamma}-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.

Key words: poly-{gamma}-glutamic acid, natto, fermented soybeans, stable isotopes, calcium absorption, post-menopausal women






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