Calcium Absorptive Efficiency Is Positively Related to Body Size

Background: Calcium absorption efficiency is a more important determinant of calcium balance than calcium intake itself. The sources of variability in absorptive performance are only partly elucidated. Purpose: The aim of the study was to explore the relationship between body size and calcium absorption efficiency. Design and Setting: Metabolic studies were performed on an inpatient metabolic unit in an academic health sciences center. Subjects: One hundred seventy-eight women, with an average age of 50.2 yr, were studied from one to five times and yielded an aggregate data set containing 633 individual studies. Methods: Calcium absorption fraction was measured by the dual-tracer method. Observed values were expressed as residuals from predicted values for each woman’s actual calcium intake, using the previously published relationship between intake and absorption. Results: Absorption residuals were significantly positively correlated with height, weight, and surface area, and after adjusting for estrogen status, these body size variables accounted for approximately 4% of the total variability. Conclusion: The magnitude of the effect is such that a woman 1.8 m in height would absorb 30+% more calcium from a given intake than a woman 1.4 m tall.