Objectives
The effect of space flight on the skeletal system is an issue that needs to be addressed to assure crew well-being during extended duration missions. This is due to the lack of a weight-bearing influence on the skeletal system which results in a loss of bone mineral. Due to the reduced gravity environment during space flight, bone mass and the levels of hormones that regulate calcium in the body significantly decrease while calcium levels in the blood increase. This indicates a disruption in calcium metabolism, or the balance of calcium in the body. The studies for this experiment were designed to provide information on the causes and possible countermeasures for bone loss caused by living in space for long periods of time.
Shuttle-Mir Missions Approach
A whole body x-ray scan was performed using Dual Energy X-ray Absorptiometry (DEXA) on the three astronaut test subjects before flight to determine baseline total body bone mass, as well as bone mass in certain body regions. An x-ray was also performed after the flight, and any loss of bone mass that occurred during flight was observed by comparing the x-rays.
Before flight, blood, urine, fecal and saliva specimens were collected from each test subject several times to determine baseline values of calcium, and bone and calcium regulating hormones. In flight, calcium absorption by the body and calcium levels in the body were studied by using a chemical tracer. Crewmembers ingested and received an injection of calcium tagged with the tracer. Afterwards, blood, urine and saliva samples were collected. Levels of the tagged calcium were determined from the samples, as well as hormones that regulate calcium in the body. The same procedure was repeated after the flight (along with the collection of fecal specimens) in order to detect changes that occurred as a result of microgravity. The investigators also monitored the re-adaptation of bone-regulating hormones and calcium metabolism after space flight.
During all phases of data collection, exercise, foods, fluids and medications consumed were recorded. The intake of certain dietary elements, especially calcium and Vitamin D, was evaluated after flight to determine the rate of calcium absorption and the mechanism by which any changes occurred. This evaluation aided investigators in understanding the impact of dietary calcium on bone loss in space.
Results
Urinary calcium excretion was higher during flight than before. Urinary collagen metabolite excretion was almost 40% greater than the preflight level. The amount of calcium absorbed by the body decreased during and after flight. Three months after flight, calcium absorption remained slightly below preflight values. These data showed that inflight bone loss was associated with increased resorption of bone minerals and decreased formation of bone.
Additional studies are needed to develop techniques to maintain bone and calcium stability during extended-duration space flight.
Earth Benefits Publications Principal Investigators
Victor Oganov, M.D., Ph.D. Co-Investigators
STS-71, Mir-18
The experiment was composed of several different components. Data was collected to monitor bone mass, bone and calcium regulating hormones, urinary indices of bone mineral loss, what the crewmembers ingested (food, fluid and medicine) and exercise.
Analysis of the blood revealed that hormone level concentrations were reduced by as much as 30-40% during flight compared to before flight. Proteins that aid in bone mineralization were increased or unchanged during flight. Vitamin D concentrations that promote proper utilization of calcium and phosphorus, thereby assisting in bone mineralization, were decreased. Serum total calcium was unchanged; the ionized fraction increased slightly. Venous whole blood pH did not change.
While investigating countermeasures for bone loss that crewmembers experience during flight, scientists hope to find preventive measures for osteoporosis, a condition in which bone structure becomes brittle.
None available at this time.
Helen Lane, Ph.D.
NASA/Johnson Space Center
Institute of Biomedical Problems
Irina Popova
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Curator:
Julie Oliveaux
Responsible NASA Official: John Uri |
Page last updated: 07/16/1999
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