Urinary Calcium for Tracking Bone Loss and Kidney Stone Risk in Space

Abstract

INTRODUCTION: Urinary calcium (Uca) levels in space reflect bone loss and kidney stone risk and could be measured using portable devices. This project evaluated the repeatability of Uca measurements to assess how many repeated measurements would be needed to detect significant urinary calcium elevations in space.METHODS: A total of six subjects collected 24-h urine samples weekly for 8 wk and took 500 mg of oral calcium carbonate and 400 IU of vitamin D daily in week 7 and 8. Uca concentration was analyzed using a calcein-based system. The effect of the intake of calcium and vitamin D on Uca levels and the correlation between first void concentration and 24-h mass were assessed with linear mixed effect models. The reproducibility coefficient (RPC) for Uca was determined using Bland-Altman analysis on pairs of measurements at different time points.RESULTS: Oral supplementation did not significantly affect 24-h mass. First void concentration correlated with 24-h mass. The 24-h mass RPCs were 167.0, 116.8, and 108.1 mg for 1-, 2-, and 3-wk average measurements. First void concentration RPCs were 90.6, 76.6, and 72.8 mg L1. Skylab astronauts 24-h mass increased by 88.9 76.0, 123.5 58.3, 142.2 56.5, and 159.9 83.4 mg after 1, 2, 3, and 4 wk in flight.DISCUSSION: Averaging multiple Uca measurements reduced variability effectively and allowed increases likely to be seen in space to be detected. Consecutive Uca measurements could be tracked over time in space to assess the effectiveness of the countermeasure program. First void concentration could potentially be used rather than 24-h collections.Ren J, Stankovic AS, Knaus DA, Phillips SD, Kynor DB, Buckey JC. Urinary calcium for tracking bone loss and kidney stone risk in space. Aerosp Med Hum Perform. 2020; 91(9):689696.

Pre-Flight Body Weight Effects on Urinary Calcium Excretion in Space

“…Previous research has shown that urinary calcium excretion can serve as a marker of bone loss and kidney stone risk while in space. (10,22,33) However, identifying which passengers may bene t from in-ight urinary calcium monitoring has not been well established. Based on the ndings of this study, preight medical screening for space ight passengers may incorporate body weight to select individuals for whom closer monitoring of urinary calcium levels may be useful while they are in microgravity.…”

Dissociation of Bone Resorption and Formation in Spaceflight and Simulated Microgravity: Potential Role of Myokines and Osteokines?

“…PTH inhibits the secretion of OPG, allowing for preferential differentiation into osteoclasts. This pronounced inhibition leads to a reduction in vitamin D production at the intestinal level, leading to decreased kidney Ca 2+ reabsorption and hypercalciuria, consequently increasing the risk of kidney stone formation [ 124 ]. Notably, there are large differences in bone density loss after a 6-month mission, typically accounting for 8–12% [ 125 ].…”

Bone loss and kidney stone risk in weightlessness

“…To assess whether this was possible, Ren et al [8] examined a unique dataset wherein 24-h urine collections were analysed void-by-void (rather than by making a single measurement on a pooled collection as is usually done). The dataset was created by having six individuals collect urine for 24-h void-by-void once a week for 8 weeks without any dietary controls.…”