Calcium absorption in postmenopausal Chinese women: a randomized crossover intervention study.

The Ca intake and food sources of Chinese postmenopausal women are quite different from those of their Western counterparts. But, little information on Ca metabolism is available in Chinese populations. We determined true fractional calcium absorption (TFCA), true Ca absorption(= TFCA x Ca intake, Va), urinary Ca excretion (Vu,) and the difference between Va and Vu, (Va-u), in response to three dietary Ca intake levels. Twenty-one healthy postmenopausal Chinese women aged 49-64 years were recruited for this randomized crossover trial from a general community, Guangzhou, China. Subjects were randomly assigned to receive 0, 500 and 1000 mg Ca/d for 5 weeks separated by 2-week washout periods. TFCA using Ca stable isotopes, total urinary Ca excretion and Ca intake were determined after 4 weeks of adaptation. Mean values for total Ca intake (Vi) of the three phases were 391 (SD 197), 880 (SD 130) and 1382 (SD 160) mg/d. On usual diet, TFCA, Vu, Va, and Va-u were 0.57 (SD 0.12), 175 (SD 59) mg/d, 216 (SD 98) mg/d and 41 (SD 99) mg/d, respectively. With the supplementations of 500 and 1000 mg Ca/d, TFCAsignificantly decreased to 0.52 (SD 0.12) and 0.43 (SD 0.13) (P<0.001); whereas urinary Ca (P=0.003), Va and Va-u increased significantly (P< 0.001). Using a mixed-effects nonlinear regression model, it was estimated that Va-u was approaching a plateau when mean Ca intake reached 1300 mg/d. In conclusion, the present findings suggest postmenopausal Chinese women have high Ca absorption efficiency and a mean Ca intake of about 1300 mg/d is required to maximize the Va-u.