Tian Tian, Tan Rong, Wang Xiaoping, Wu Jigong, Gu Jianwen, Jia Haiying, Yang Yuan, Zhang Li, Liu Xin, Wang Yuan, Sun Bo, Yang Kai, Gao Junfeng, Gao Chuan, Strategic Support Force Characteristic Medical Center, Spine Surgery, Neurosurgery, Shenzhou Medical Team, Aerospace Clinical Medicine, and Special Service Health Center
In the 21 years since Yang Liwei asked the sky in 2003, China's manned space program has made remarkable achievements, and 20 Chinese have left a presence in the vast space. With the normalization of manned missions in the space station stage, the number of astronauts who have exceeded 200 days in orbit has reached three, namely Jing Haipeng who has patrolled the sky four times, Chen Dong and Tang Hongbo who have flown twice.
However, osteoporosis in long-term weightlessness has become a major health challenge for astronauts. Quantitative CT analysis of the distal tibia of astronauts who had been flying for 6 months showed a 24% loss of cancellous bone. The following are the causes of osteoporosis.
- Effects of weightlessness: In weightlessness, due to the lack of normal gravity load, the human bone tissue undergoes a process of remodeling, resulting in a decrease in bone density and bone strength, a phenomenon known as weightless osteoporosis. The results showed that: (1) stress stimuli such as gravity are important factors for maintaining normal bone metabolism, (2) there is a clear causal relationship between weightlessness and osteoporosis, (3) the rate of bone loss in weightlessness is faster than that of postmenopausal women, and (4) the longer the weightlessness time, the more severe the bone loss.
- Cosmic ray action: Space station missions or deep space missions inevitably expose you to a variety of ionizing radiation, such as solar particle events, cosmic background rays, and Earth radiation belts, including electrons, protons, and heavy ions. It has been found that both ionizing radiation and microgravity affect osteoclast activity, and radiation doses of 0.1Gy affect their activity, and there is an overlapping effect with microgravity. When the radiation dose is too high to exceed 0.5 Gy, osteocyte activity decreases.
- Biological changes in bone tissue osteoblasts: In weightlessness or simulated weightlessness, there is an imbalance between bone formation and bone resorption, that is, bone resorption is greater than bone formation. It has been found that osteoclasts transfer small nucleic acid molecules (microRNA-214) affected by gravity to osteoblasts through exosomes, which inhibits osteoblast function and leads to osteoporosis.
Measures to combat bone loss are as follows.
- Exercise: It mainly includes the use of treadmills, bicycle power meters and resistance training devices. In contrast, monthly bone loss can be reduced from 1.0% to 0.3%-0.5% after exercise, but it still does not completely resist the progression of osteoporosis. The reasons are: (1) the stress exerted by machinery in space on the human body cannot reach a level similar to or higher than that of Earth's gravity, and (2) the duration of exercise is not sufficient to maintain the metabolic needs of bone.
- Pharmacotherapy: Trace elements such as active vitamin D, vitamin K and zinc can improve bone metabolism and are important nutrients to be supplemented during long-term space flights.
The treatment of osteoporosis mainly includes the following:
- Lifestyle modifications: Maintain a balanced diet with adequate calcium and vitamin D, moderate exercise such as walking, swimming, etc., and avoid smoking and excessive alcohol consumption.
- Calcium and vitamin D supplementation: Calcium and vitamin D supplementation are appropriate on an individual basis.
- Medications: Anti-bone resorption drugs: such as bisphosphonates, estrogen, etc., to reduce bone loss. Bone-promoting drugs, such as teriparatide, help increase bone density. Others: such as strontium salts, etc.
- Fall prevention: Take steps to reduce the risk of falls to prevent fractures.
- Rehabilitation treatment: including physical therapy, rehabilitation training, etc.
- Regular monitoring: Regular bone density testing is performed to evaluate the effect of treatment.
- Treatment of underlying diseases, such as diabetes, hyperthyroidism, etc., to reduce the impact on bone metabolism.
- Health education: Raise awareness of disease and enhance self-management skills.
Treatment should be individualized based on the patient's specific situation, such as age, sex, bone mineral density, underlying medical conditions, and other factors. At the same time, during the course of treatment, regular follow-up examinations are required to monitor changes in bone density and other relevant indicators.
In short, with the advancement of the continental manned space mission and the implementation of the future deep space exploration plan, the time of astronauts in orbit will continue to be extended, and the impact of medium and long-term weightlessness on bone health will become more and more significant. Future research will continue to explore the biological changes of bone tissue in weightlessness and how to effectively prevent and treat weightless osteoporosis.
Bibliography:
[1] Tan Rong, Gu Jianwen.Research status of bone health management of astronauts in medium and long-term flight[J].Chinese Journal of Osteoporosis, 2020, 26(6):5.)
【2】A novel long noncoding RNA AK016739 inhibits osteoblast differentiation and bone formation.
【3】Role of the IGF-1 system in bone metabolism.
【4】A perspective on bone health in space.