The TBone studies: Effects of microgravity on astronauts' bones
The Canadian TBone experiment used 3D imaging technology to study changes in astronauts' bone health caused by the time they spend in space. Its successor, TBone2, is continuing this work
Results
The TBone experiment confirmed that although astronauts on the International Space Station (ISS) follow daily exercise programs, bone loss progresses proportionally to the length of their missions. An astronaut's skeleton, floating in microgravity, appears to age at an accelerated rate during a six-month stay in space – the equivalent of almost 20 years of bone loss on Earth. The study's findings also suggest that increasing exercise during their mission as opposed to pre-flight is more likely to preserve bone strength while spending time away from Earth's gravity.
Data collected during the TBone study also allowed researchers from Canada, the United States and Germany to study the structure of the tibia in 14 astronauts for up to one year after their return from the ISS.
Results from their analysis showed that:
- Even after a year on Earth following their missions, more than 50% of the astronauts who participated in TBone had not regained their pre-flight bone density.
- Astronauts who spent less than six months in space recovered more bone than those who lived in space for over six months.
- Bones age differently in space than they do on Earth! The researchers noticed differences between the bone loss caused by microgravity and bone loss that occurs naturally during aging. On Earth, the external part of the bone becomes fragile more quickly than the interior part of the bone as a person ages. But in space, the effect is the opposite: the internal part of the bone becomes weaker faster than its exterior.
These findings have important implications for future space travellers headed to distant destinations like Mars, and for patients on Earth who are immobilized or injured for long periods of time.
Background
Our bones constantly undergo a reshaping process in response to everyday use. On Earth, bones are optimized for working in gravity, the force they must work against to support our body weight.
Due to weightlessness and reduced exercise, more bone is lost than replaced during extended space flight.
While adults past age 50 typically lose about 1% of their bone mass each year (a process that can eventually lead to osteoporosis), astronauts in space can lose up to 1.5% each month. Fortunately, much of this loss is reversed when astronauts return to Earth.
Researchers want to know whether bone loss might reach its highest levels during the first six months of space flight and continue afterward, as astronauts remain in space.
The objective of the TBone investigation was to determine how this cycle of loss and regain affects the long-term strength and quality of bones. TBone2 is continuing to investigate the mechanisms of bone loss and regain in astronauts undertaking missions of up to one year on the ISS.
Studies like TBone and TBone2 could:
- help space travellers stay healthier during longer missions
- enable humans to travel farther into space
- allow experts to identify who is more susceptible to bone loss caused by inactivity
Effects of microgravity on bones with astronaut Tim Peake. (Credits: Canadian Space Agency, NASA, European Space Agency)
Human bones contain a honeycomb-like structure that helps give support and strength. When we walk, dance, play hockey, and enjoy other forms of exercise, the force required for us to work against gravity in order to carry our own body weight regenerates our bone tissue, and makes our skeletal system stronger. When we are less mobile, our bones lose density and strength.
Objectives
TBone
Using high-resolution imagery, TBone's researchers:
- investigated how weightlessness in space flight changes the interior structure of bones
- learned more about how those changes reverse once astronauts return to Earth
- created a list of factors that could help doctors predict who is likely to experience greater bone loss and who is at higher risk of fractures
TBone2
Researchers will:
- build on the knowledge gained from TBone by studying astronauts who spend varying amounts of time on the ISS – including short-duration, six-month and one-year flights
- help determine the risks of very long space flights, which could become more common in the future
Impacts on Earth
"What we can learn in six months of space flight would take us a decade on Earth," said Dr. Steven Boyd, TBone's principal investigator.
TBone offered researchers a better understanding of diseases like osteoporosis, a bone loss disorder that affects approximately 10% of the Canadian population aged 40 and over. According to Osteoporosis Canada, at least 1 in 3 women and 1 in 5 men will break a bone due to osteoporosis in their lifetime. Further research could help identify those who are prone to bone loss, and design individualized treatment strategies to predict and prevent fractures caused by low bone density.
How it works
TBone
Seventeen astronauts participated in this study.
- Participants underwent high-resolution 3D imaging of their wrists and ankles before and after their missions. This created a comparative picture of the microscopic shapes and structures inside the bones.
- Throughout their mission, astronauts provided blood and urine samples for many studies. The data from these samples was shared under an international agreement, and was used for TBone to understand the factors involved in bone adaptation.
- Scientists also kept careful records about factors that could affect the results, such as food intake, medication, supplements, and exercise routine.
TBone2
Thirty astronauts will take part in this study.
- Participants will undergo high-resolution 3D imaging of their wrists and ankles before and after their missions.
- Data will be gathered from the same group of astronauts during other CIPHER experiments – such as ones that examine the effects of space flight on blood, the cardiovascular system, and stress. This will add knowledge to the TBone2 findings.
As part of NASA's CIPHER program, TBone2 is examining subjects who take part in space flights of six weeks, six months, and one year – longer than the original TBone study. Comparing how astronauts' bodies react to different lengths of time exposed to microgravity, will help researchers test a hypothesis: that bone loss happens most during the first six months of space flight and then stabilizes within one year in space.
TBone2 is one of two Canadian Space Agency studies that are part of NASA's CIPHER program. The other is Vascular Calcium.
CIPHER, which stands for Complement of Integrated Protocols for Human Exploration Research, brings together specially selected studies to be conducted on the ISS. CIPHER is designed to help better understand the impact of long-duration space flight by comparing the effects of different mission lengths: short stays, standard six-month missions, and long-duration (one-year) space flights.
Timeline
- The TBone team began collecting data in . The research concluded in .
- The TBone2 team began its data collection in .
Astronauts in space get about two hours of exercise each day, which helps prevent some of the bone loss that occurs in microgravity. (Credit: NASA)
Research team
Dr. Steven Boyd of the University of Calgary is the principal investigator for the TBone series.
His co-investigators for TBone were:
- Dr. Leigh Gabel, University of Calgary
- Dr. Paul Hulme, University of Calgary
- Dr. Anna-Maria Liphardt, German Sport University in Cologne, Germany
- Dr. Martina A. Heer, University of Bonn, Germany
- Dr. Jean Sibonga, NASA
- Dr. Scott M. Smith, NASA