|Abrams, Steven -|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: October 10, 2010
Publication Date: June 1, 2010
Citation: Abrams, S.A. 2010. In vivo calcium metabolism by IRMS. In: Gross, M.L., Caprioli, R.M., editors-in-chief. The Encyclopedia of Mass Spectrometry: Elemental and Isotope Ration Mass spectrometry. Volume 5. Oxford, UK: Elsevier. p. 990-996. Technical Abstract: Public policy initiatives related to enhancing the health of populations, increasingly seek to identify meaningful biological outcomes on which to determine age-related nutritional requirements. For calcium, the primary outcome of interest is the availability of calcium in the diet for bone formation and remodeling. However, dietary absorption of calcium can vary from as little as 10% in an older person ingesting the calcium from a supplement pill given without a meal, to 70-80% in a breast-fed infant or a pregnant woman receiving a small, highly bioavailable calcium source given with a meal. As such, developing dietary requirements for any nutrient without consideration of bioavailability, as well as, life cycle and related factors is impractical and likely to lead to misleading conclusions. It is necessary to understand the causes and implications of these variations in dietary absorption to make rational nutritional recommendations. Furthermore, in disease processes or with the administration of systemic steroids, dietary calcium may decrease in bioavailability and bone destruction may occur. These issues may be evaluated using stable isotopes in patient populations in which bone biopsies or other modes of evaluation are not possible. Recent studies using stable isotopes have clarified some of these issues. For example, it has been shown using stable isotope studies that calcium absorption increases during puberty and pregnancy, and decreases after menopause. Calcium absorption is relatively unaffected by serum calcium or bone mineral status. There is a close relationship between vitamin D status and calcium absorption, although some aspects of this remain uncertain, especially the relationship in children and the consequences of various levels of 25- hydroxyvitamin D in the serum on calcium absorption.