Estimation of True Calcium Absorption in Men

When both calcium intake and calcium absorption are measured under controlled conditions, variation in absorption efficiency explains more of the interindividual differences in balance than does actual calcium intake (1). Small wonder, therefore, that interest in measuring absorption has remained high for nearly 40 years.True calcium absorption is defined as the quantitative, unidirectional flux of calcium from intestinal lumen into the blood. It is most accurately measured by a dual-tracer method, with one tracer labeling the oral calcium load and the other labeling the miscible calcium pool into which the absorbed calcium is introduced. This approach was first developed into a practicable human test by deGrazia et al. (2). As described, it is usually time-consuming and expensive. To reduce these barriers for widespread use, Heaney and Recker (3)(4) developed a single-tracer variant for women, requiring only a single blood sample, and calibrated it against a simultaneously performed double-tracer method. The single-tracer method has been used efficiently in thousands of women (5). However, because the calibration is empirical and based on body-size variables, it is not directly suitable for use in men who, with a typically higher proportion of fat-free mass than women, would be expected to distribute absorbed tracer in a larger mass of calcium.To fill this methodologic gap, we performed a small set of parallel measurements in adult men, using the female-based algorithm together wiketh a modified double-tracer approach.Participants in the study were 30 Caucasian men (age range, 20–60 years; weight range, 63.5–104 kg; height range, 1.67–1.93 m). All participants were free of known diseases affecting bone remodeling or calcium homeostasis, and tests were not performed if the individual had experienced any gastrointestinal disturbance in the preceding 5 days. Each gave informed consent after the procedures of the study were explained. Both the project …