Prolonged weightlessness and calcium loss in man

Area of Science:

• Space medicine
• Skeletal physiology
• Bone metabolism

Background:

• Extended orbital space flight exposes astronauts to microgravity.
• Understanding the long-term skeletal consequences is crucial for astronaut health.
• Previous studies suggest bone loss occurs during space missions.

Purpose of the Study:

• To predict the long-term skeletal consequences of weightlessness.
• To quantify calcium loss during prolonged space flight.
• To compare space flight-induced bone demineralization with terrestrial conditions.

Main Methods:

• Analysis of accumulated data from men in orbital space flight up to 12 weeks.
• Measurement of daily calcium loss (urinary and fecal).
• Assessment of plasma parathyroid hormone, calcium, and phosphorus levels.
• Evaluation of bone mineral mass in the calcaneus, ulna, and radius.

Main Results:

• Exponential acceleration of calcium loss from 50 mg/d at 1 week to 300 mg/d at 12 weeks.
• Hypercalciuria stabilized within 4 weeks; fecal calcium losses increased throughout.
• Diminished gastrointestinal absorptive efficiency observed.
• Slight decrease in parathyroid hormone and slight increase in plasma calcium and phosphorus.
• Calcaneus mineral loss correlated with calcium imbalance; ulna and radius showed no changes.

Conclusions:

• Space flight-induced bone demineralization is more severe than predicted from immobilized subjects.
• The observed skeletal changes may not be entirely reversible.
• Further research is needed to understand and mitigate space flight-related bone loss.