Calcium metabolism before, during, and after a 3-mo spaceflight: kinetic and biochemical changes

Abstract

The loss of bone during spaceflight is considered a physiological obstacle for the exploration of other planets. This report of calcium metabolism before, during, and after long-duration spaceflight extends results from Skylab missions in the 1970s. Biochemical and endocrine indexes of calcium and bone metabolism were measured together with calcium absorption, excretion, and bone turnover using stable isotopes. Studies were conducted before, during, and after flight in three male subjects. Subjects varied in physical activity, yet all lost weight during flight. During flight, calcium intake and absorption decreased up to 50%, urinary calcium excretion increased up to 50%, and bone resorption (determined by kinetics or bone markers) increased by over 50%. Osteocalcin and bone-specific alkaline phosphatase, markers of bone formation, increased after flight. Subjects lost ∼250 mg bone calcium per day during flight and regained bone calcium at a slower rate of ∼100 mg/day for up to 3 mo after landing. Further studies are required to determine the time course of changes in calcium homeostasis during flight to develop and assess countermeasures against flight-induced bone loss.

Calcium and bone metabolism during space flight

“…Increased calcium excretion is a major contributor to the increased risk of renal stone formation 24 This fits very closely with the Skylab calcium balance data, which showed whole-body calcium losses of200 to 300 mg/d. l While early hypotheses suggested that space travelers' serum concentrations of total and ionized calcium would increase, only very small changes have been noted, and those have had only statistical rather than clinical significance.…”

“…24 ,30,3 1,3 5,36 Calcium tracer kinetic data also indicated that bone resorption increased about 50% during flight. 24 Because of the increasing use of collagen crosslinks as markers, a few comments are warranted about common perceptions and misconceptions. Critics of using collagen crosslinks often point out that they vary considerably from day to day and from subject to subject, and this criticism is well founded.…”

Challenges, concerns and common problems: physiological consequences of spinal cord injury and microgravity

“…111,112 There is a growing body of evidence from NASA and the Russian space program showing that humans exposed to the microgravity environment of space also have a greater risk for developing renal stones. 100,113 Should such stones develop on long-duration missions, debilitating pain accompanying the stone incident would result in functional loss of the crew member and that person's contribution to overall success of the mission. Lack of facilities for in-flight treatment of a stone episode could furthermore necessitate aborting the mission and initiating a rapid return to Earth.…”

Lower body negative pressure treadmill exercise as a countermeasure for bed rest-induced bone loss in female identical twins

“…Data from Skylab and Mir missions show that astronauts continue to lose bone despite participation in vigorous in-flight exercise protocols [11,26,35,41]. The inflight exercise program on early International Space Station (ISS) flights was also not successful at mitigating weightlessness-induced bone loss [25], although exercise hardware availability in those missions was inconsistent.…”