Fun fact: One day in heaven equals one week on earth? Do people in heaven live longer?

From 2015 to 2016, NASA conducted a one-year "twin experiment" on the International Space Station. During the experiment, the younger brother of a pair of identical twin astronauts, Scott Kelly, stayed on the International Space Station for 340 days, while his older brother, Mike Kelly, stayed on Earth to carry out the twin mission with Scott. Scientists on the ground also observed the lives of the two brothers and regularly extracted blood samples for analysis throughout the mission. This allowed them to compare the similarities and differences in the physiological data of the two brothers before, during and after their stay on the International Space Station. This experiment studied the effects of the space environment on ten aspects of the human body, including gene expression, physiological changes, immune function, and cognitive ability.

Twin astronauts in NASA's "Twins Experiment" (Image source: NASA official website)

The "Twins Experiment" has achieved many research results, one of which is that the telomeres of people in space will become longer. Since the lengthening of telomeres means a slowing down of the aging process, does it mean that long-term space flight will extend human life?

Let's first understand what telomeres are. Telomeres are small segments of DNA-protein complexes that exist at the ends of chromosomes and are used to protect the main part of DNA from damage during cell division. The length of telomeres reflects the cell replication history and replication potential. As we age, the length of telomeres tends to shorten. The shorter the telomere, the shorter the life span of the cell; the longer the telomere, the stronger the cell's regeneration ability. Therefore, the length of telomeres means the degree of aging.

Telomeres are located at the ends of chromosomes (Image source: NASA official website)

Sadly, however, NASA researchers found that within a few days of Scott's return to Earth, most of his telomeres had shortened again, returning to the same length as Michael's.[1] The reasons for both lengthening and shortening are complex, and scientists are still investigating. Astronauts' rigorous exercise and balanced calorie intake on the International Space Station are beneficial for maintaining telomere length, so a healthier lifestyle can extend life, both in space and on Earth.

In fact, space is not the immortal wonderland in myths. A series of research results, including NASA's "twins experiment", show that the space environment is not friendly to us. Without considering the harsh factors such as high vacuum, strong radiation, and extreme temperature, just in terms of gravity, humans have lived on Earth for hundreds of thousands of years, and their bodies have evolved to adapt to the Earth's gravity environment. At present, it seems that humans still have many inadaptability and medical problems to be solved in microgravity.

Why do astronauts’ immune functions decline after long-term flights? Experiments conducted on the space shuttle, Russian aircraft, and the International Space Station have shown that immune cell signals and cytokines change in microgravity, indicating that the immune system is suppressed under microgravity conditions. Of course, in addition to microgravity, physiological stress, circadian rhythm disorders, radiation, and other space factors may also affect astronauts’ immune responses [2].

Regarding the phenomenon of cardiovascular and cerebrovascular function degradation, scientists have found that in a microgravity environment, the shape of the human heart changes, and the muscles used to constrict blood vessels atrophy, which leads to a decline in cardiovascular and cerebrovascular functions, such as the ability to regulate blood pressure [3]. For example, Scott's carotid artery dilated during his stay on the International Space Station, and the innermost two layers of his carotid artery wall thickened. Scientists speculate that this may be related to potential cardiovascular and cerebrovascular diseases.

Muscle atrophy and bone loss (decreased bone density) are all related to the low dynamic state of humans in a microgravity environment, which can be effectively alleviated by carrying out reasonable exercise in space. Research on the causes and mechanisms of bone loss is not only beneficial to the health of astronauts, but also helps solve problems such as decreased bone strength caused by human aging on Earth.

Astronauts who have undergone long-term space flight also experience decreased vision. Interestingly, this problem seems to be more serious in male astronauts than in female astronauts. Experiments on mice and on-orbit tests of astronauts have shown that space flight affects cerebral vascular resistance and contractility. Some astronauts experience increased intracranial pressure and visual impairment [4].

Astronauts perform eye ultrasound imaging examinations on the International Space Station (Image source: NASA official website)

On the other hand, psychological problems are also problems that humans have to face when surviving in space. With the complexity of flight missions and the continuous increase in the number of crew members in a closed environment, the interpersonal relationships and psychological states of space station crew members will become increasingly complex and difficult to deal with, thus causing psychological barriers for astronauts and affecting their work and health.

Despite this, human beings will not stop exploring space. With the development of aerospace technology, interstellar migration may become a reality. However, the microgravity environment, cosmic rays, and closed space capsules in space may have an impact on human physiological and mental health. Before the curtain of interstellar travel is raised, it is particularly important to scientifically and rigorously evaluate the impact of the space environment on human health. There are many aerospace medical experimental projects in the Chinese space station to study the impact of the space environment on the human body and countermeasures. It is believed that a large number of results will be produced to benefit mankind.

References:

[1] NASA's Twins Study Results Published in Science Journal. NASA official website.

[2] Scientists Probe How Long-Term Spaceflight Alters Immunity. NASA official website.

[3] Cardiovascular Health in Microgravity. NASA official website.

[4] Fluid Shifts Before, During and After Prolonged Space Flight and Their Association with Intracranial Pressure and Visual Impairment. NASA official website.

[5] Aitian Space Science Center. Giant pandas roaming the Chinese space station.

Scientific review: Li Yinghui, deputy chief designer of the astronaut system of China's manned space program, academician of the International Academy of Astronautics