Time dilation, a concept of Einsteins, occurs when an object moves close to the speed of light. For astronauts traveling at near-light speeds, time would pass more slowly for them relative to people on Earth.

In theory, astronauts could age slower compared to individuals on Earth if they were to travel at such speeds. However, this is not relevant to current space travel, as the speeds required for significant time dilation effects are far beyond the capabilities of today's spacecraft.

So, do astronauts age just like us, earthbound people?

A little bit about radiation in space and telomers in your DNA
Space radiation is high-energy particles and electromagnetic radiation found outside of Earth's protective atmosphere, mainly coming from the Sun and outer space. These particles travel at nearly the speed of light and are capable of penetrating spacecraft and living organisms, potentially causing serious damage to our DNA.

Telomeres are the protective caps at the ends of our chromosomes, like the plastic tips on shoelaces. They help keep our DNA intact. As cells divide, these telomeres get shorter, which happens naturally with aging, stress, lifestyle habits, and environmental factors. Because of this, the length of telomeres can be used as a biomarker for a person’s overall health, how fast they are aging, and their risk for age-related diseases.

Astronauts face unique biological challenges during space travel, including exposure to ionizing space radiation. Research shows that astronauts returning from space have elevated levels of TERRA. TERRA plays a critical role in protecting the ends of our chromosomes, our telomeres, which are particularly vulnerable to radiation damage.

These increased levels of TERRA suggest that the astronauts are actively responding to the radiation-induced damage to the telomers in our DNA. This heightened response indicates that the body is working to repair the harm caused by space radiation, a crucial process for maintaining cellular health during and after space missions.

Simulated conditions
Individuals exposed to high-altitude environments, such as climbers on Mount Everest, have shown similar increases in TERRA.

Radiation levels at Mount Everest are significantly higher than at sea level. This higher exposure is primarily due to cosmic rays, which are less shielded by the thinner atmosphere at high altitudes. Everest climbers can receive up to 100 times more radiation than at sea level.

This suggests that the combination of low oxygen and increased radiation exposure at high altitudes mimics the stress astronauts experience in space. Such environments also lead to changes in telomere length, further supporting the link between TERRA and cellular stress response mechanisms.

The role of TERRA in DNA damage repair
Laboratory studies demonstrated that TERRA is not just a passive marker of telomere damage but actively participates in repairing broken DNA.

When DNA breaks at the end of the chromosomes, the telomeres, TERRA binds to the damaged sites, forming protective structures that prevent further degradation.

The research also suggests that TERRA may facilitate the recruitment of other repair proteins, enhancing the cell’s ability to restore damaged DNA. These repair mechanisms are vital for maintaining the integrity of our DNA - especially during prolonged space missions where radiation exposure is continuous.

So space travel and aging?
Besides the increase in TERRA, research on astronauts during space missions shows notable changes in their telomeres. In a study involving astronauts from both 6-month and 1-year missions aboard the International Space Station, scientists observed that telomeres lengthened during spaceflight. This was unexpected, as telomeres typically shorten over time.

However, after returning to Earth, the astronauts experienced rapid telomere shortening, and overall, their telomeres were shorter than before the mission. This change was consistent across astronauts, regardless of the mission length.

The study also noted signs of chronic DNA damage and chromosomal changes, which persisted even after the astronauts returned to Earth. These effects suggest that spaceflight might cause long-term instability in the DNA.

While space travel might offer some transient benefits in terms of reversing certain biological effects, it does not make astronauts biologically younger in the overall sense. The radiation and microgravity environment is more likely to accelerate certain aging processes, especially at the cellular and genetic levels.

The insights from space and Everest have broader implications beyond space travel, though. Understanding how TERRA and telomers function in extreme environments could lead to new therapeutic strategies for conditions involving chronic DNA damage, such as certain cancers or age-related disorders. It could potentially improve radiation therapy outcomes and minimize side effects - and enhance human resilience in space.

About the scientific papers:

First author: Taghreed M. Al-Turki. USA
Published in: Communications Biology, June 2024
Link to paper: https://pmc.ncbi.nlm.nih.gov/articles/PMC11167063/pdf/42003_2024_Article_6014.pdf

First author: Jared J Luxton, USA
Published in: Cell Reports, December 2020
Link to paper: https://www.cell.com/cell-reports/fulltext/S2211-1247(20)31424-8?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS2211124720314248%3Fshowall%3Dtrue