Abstract
Background: Variation in absorption efficiency explains more of the variability in calcium balance than does actual calcium intake. Several investigators have suggested that the relatively high phosphorus and protein intakes of the diets of industrialized nations reduce calcium absorption and thereby aggravate the problem of calcium deficiency. Objective: My objective was to test whether variation in phosphorus and protein intakes is associated with variation in calcium absorption. Design: One hundred ninety-one Roman Catholic nuns aged 48.7 ± 7.0 y were studied ≃3 times each over a >20-y period with a full metabolic balance regimen; controlled, chemically analyzed diets; and double-tracer measurement of calcium absorption. Results: Although the expected associations with absorption were found for age, calcium intake, and estrogen status, no association was observed for intakes of either phosphorus or protein. Conclusion: Phosphorus and protein intakes do not contribute to the wide variability in calcium absorption efficiency.