What's the effect of microgravity on aging and do we age slower in space?

Travelling to outer space is becoming a thing of our very near future, but we don't know what happens to our body in the absence of gravity yet. Should we believe all the science fiction movies where people don't age in space or other planets, or do people actually age faster in space? 

Is microgravity the ultimate anti-aging solution, or does it cause us to age faster than usual? Keep reading to find out! 

What is gravity?

We must first better understand gravity to explore its effects on us. Gravity is the force by which a planet or similar body pulls objects toward its center. It is the force that pulls you back down to the ground when you jump and makes objects fall. Everything that has mass will also feel the pull of gravity (1). 

The magnitude of gravity you feel won't be the same on Earth, the moon, or in free outer space. This is because the amount of gravity that an object (e.g. a planet) has on you depends on the mass of that object. If you went to the moon, which weighs less than the Earth, the gravity would be weaker. That's why black holes have such a big gravitational force - they pack so much mass in a small space. 

What is microgravity?

On the other hand, microgravity is a very weak form of gravity usually present in an orbiting spacecraft. It is not to be confused with zero gravity, as a small amount of gravity is present everywhere in space, and true zero gravity doesn't really exist. 

In fact, astronauts at the International Space Station (ISS) feel 90% of Earth's gravity and are constantly being pulled toward the Earth. However, as all objects in the spacecraft fall towards Earth simultaneously, and no other forces are present, they are in constant free fall. This makes them appear to float, and to some, it may seem like they are under zero gravity, which is misleading. 

Because of these conditions, we can study what happens to humans under gravity, which is lower than the Earth's one. There have been many studies on the effects of microgravity on the human body, mostly coming from the brave astronauts who spent months or years aboard the ISS.

Did these astronauts have more or less health complications when they were in space? And did their space travelling make them age faster or slower when they returned to Earth? Let's explore the scientific findings. 

The effects of microgravity on the human body

If you've seen movies like Interstellar or Planet of the Apes, you probably remember how certain characters aged much slower in space or other planets when compared to those they've left on Earth. The thing is, we're not there yet. All of our current knowledge on aging in space comes from the ISS, which still has a very similar gravitational pull as the Earth does.

Nonetheless, we're lucky to be able to do many different experiments in microgravity, and to already see significant changes in human metabolism, only under 90% of the gravity we usually feel. These are some findings on what happens to humans in microgravity (2):

1. Loss of muscle and bone density - in microgravitational conditions, astronauts significantly lose muscle and bone density. They often experience similar symptoms to sarcopenia and osteoporosis, which are more common among older people. The reason for this might simply be because they don't need to use their muscles as much as they do on Earth. 
2. Changes in the cardiovascular system - astronauts experience several negative effects of microgravity on their hearts and blood vessels. Blood and other fluids shift toward the upper body due to the lack of gravity. The heart becomes more spherical, and astronauts experience reductions in aerobic capacity. These changes mirror age-related heart issues on Earth.
3. Microgravity weakens the immune system, making astronauts more susceptible to infections. Immune cells show reduced functionality in space, and the outcome might be similar to immune system reductions in older people. 
4. Microgravity lengthens the telomeres, the protective caps on top of our chromosomes, while normal aging makes them shorter and shorter. This was especially true for immune cells called leukocytes. Unfortunately, it's not good news, because those same telomeres tended to significantly shorten as soon as the astronauts went back to Earth (3, 4). If we were to stay in space forever, they might stay longer, but we can't say that with certainty yet. 
5. Memory issues - a long stay in space caused memory loss and changes in neural connectivity in astronauts. Microgravity also changed the distribution of brain fluid, resembling symptoms similar to Alzheimer's. 

NASA's Twins Study

One of the most useful studies on human aging in space was done by NASA in 2015 on a pair of twin astronauts (5). One twin, named Scott Kelly, spent one year aboard the ISS, while his identical twin brother, Mark Kelly, stayed on Earth. Since identical twins share exactly the same DNA, this study helped scientists better understand the impacts of space flight on human bodies. These findings are different from the others where genetic differences could significantly impact how somebody ages. 

What did NASA's scientists discover when studying Mark and Scott's bodies after a year? Let's explore the major findings (6):

• Scott's body mass decreased by 7% in one year, but it returned to normal after he returned to Earth. 
• The researchers found that Scott had markers for inflammation and carotid artery wall thickening during and immediately after his mission, but Mark had no similar changes.
• Scott's telomeres extended in space but rapidly shortened after he returned to Earth, now being even shorter than his brother's. The same was observed for his other epigenetic changes (7). 
• After a year, Scott had the same gut microbiome diversity as Mark on Earth. 
• Scott's and Mark's cognitive performance remained the same throughout the year Scott spent in space. 
• The flu vaccine worked in space exactly how it did on Earth. 

In addition to these major findings, scientists identified key genes that should be targeted for monitoring the health of future astronauts. These genes regulate the immune system, bone formation, and telomere expression. 

Conclusion

In conclusion, the effects of microgravity on the human body show both promising and health-threatening aspects when it comes to aging in space. For example, telomere lengthening might be a potential anti-aging benefit, but muscle loss, cardiovascular changes, and inflammation suggest accelerated aging. Telomeres also happened to go back to a much shorter length once people came back to Earth, making this discovery a bit less fun. 

NASA's Twins Study told us a lot about non-genetically related changes of a human body in space, but we still need to answer many questions. At one point in time, it's possible that space travel will become more accessible and we will need to understand how our bodies react in lower gravity fields. This will be the future of space medicine, and who knows, maybe telomeres remain longer in space indefinitely. 

Literature sources:

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