Microgravity inhibits intestinal calcium absorption as shown by a stable strontium test

Authors


Institut für Ernährungswissenschaft, Universität Bonn, Germany (A. Zittermann, K. Scheld, P. Stehle); DLR-Institut für Luft- und Raumfahrtmedizin, Cologne, Germany (M. Heer, P. Rettberg, C. Drummer, G. Horneck); Laboratoire de Biologie du Tissu Ossoux, Faculte de Medicine, St. Etienne, France (A. Caillot-Augusso, C. Alexandre); Institute of Biomedical Problems, Moscow, Russia (D. Vorobiev).Correspondence: Associate Professor Armin Zittermann PhD, Department of Nutrition Science, University of Bonn, Endenicher Allee 11–13, 53115 Bonn, Tel.: + 49 228732016; fax: + 49 228733217; e-mail: a.zittermann@uni-bonn.de

Abstract

Little is known about the onset and degree of biochemical and functional alterations in calcium metabolism during microgravity.

To evaluate the effect of microgravity on intestinal calcium absorption and calcium-regulating hormones under metabolic ward conditions.

Fractional calcium absorption (Fc240 in percentage of dose administered) was determined pre-flight, in-flight and post-flight, by use of a stable strontium test in one cosmonaut who spent 20 days in space. Moreover, a sequence of blood samples was collected for the determination of serum parathyroid hormone (PTH), 25-hydroxyvitamin D, calcitriol and serum C-telopeptide (CTx, biomarker of bone resorption) levels. During all periods of data collection, calcium intake was held constant at a minimum level of 1·000 mg day−1 and a daily supplement of 16·6 µg vitamin D2 was given. Personal ultraviolet (UV) light exposure was measured during the whole mission using a biologically weighting UV dosimeter.

Fc240 was markedly reduced on flight day 19 (4·4%) as compared to pre-flight and post-flight data (13·4% and 17·2%, respectively). Serum calcitriol levels fell from 40·6 pg mL−1 (mean pre-flight level) to 1·3 pg mL−1 on flight day 18 and returned into the normal range after recovery. Serum CTx increased during the flight, while serum PTH and 25-hydroxyvitamin D levels did not change significantly.

Intestinal calcium absorption can be diminished after only three weeks of microgravity. Changes are associated with a severe suppression of circulating calcitriol levels, but are independent of exogenous vitamin D supply and serum PTH levels.

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