and humanity gets closer to sending people back to the moon — or even sending astronauts to Mars —

we need to know how our bodies will handle long-term space travel.

And, thanks to the largest study ever published on the topic,

we now have a picture that's coming into focus...and that picture is full of challenges.

Back in 2019, NASA published the first ever space twin study.

This compared twins Mark and Scott Kelly before, during, and after Scott spent 340 days in space —

that's the longest any U.S. astronaut has consecutively spent in spaceflight — while Mark stayed here on Earth.

That study gave us so much insight into how the human body changes in microgravity:

from telomere shortening to gut microbiome changes to rapid alteration of gene expression.

It also told us there was still so much to learn...and boy, did 2020 deliver.

A set of nineteen new studies builds on the results of the Kelly Twins study,

reanalyzing some of that data and comparing those results to measurements between 56 astronauts in total.

Plus ten more papers are in pre-print now, being reviewed and set for publication soon to add even more to this data set.

This is the largest study of its kind, the most information EVER collected about what happens to the human body in space.

So, what did we find?

The researchers have identified, for the first time, a core set of mammalian adaptations in response to spaceflight.

We see these changes across species: humans, mice and other animals.

The biggest one?

Mitochondrial dysfunction.

You may think of the mitochondria as that famous 'powerhouse of the cell'—

it generates most of the energy a cell needs and so enables the proper function of all your tissues and organs.

So, as you might imagine, keeping your mitochondria working is pretty important.

Using new techniques that allowed a really in-depth look at changes in the astronauts' genomes and protein expression,

mitochondrial changes were consistent across the dataset.

And even though the scientists are still unsure what EXACTLY may be the underlying cause of this mitochondrial disturbance,

they think it's likely oxidative stress caused by the extreme environment of space.

This, essentially, is damage caused to cells by stress.

Stress releases these harmful compounds called reactive oxygen species, causing genetic changes

that, in turn, cause changes in metabolic pathways.

And honestly, the 'changes' they describe in this dataset are hilariously complicated.

But the upshot of the whole mitochondrial discovery is that it gives us a way to put together a lot of the pieces.

See, changes in mitochondrial function are likely the underlying cause of a lot of the other weird stuff we see in astronauts,

like disrupted circadian rhythm, immune system dysfunction, and changes in organ activity.

Because that was the other main discovery.

Turns out, space is really hard on your liver!

The liver undergoes more changes in gene and protein expression than any other organ while in space.

And this is because your liver, with its role in blood filtration,

is really important in sensing changes in blood composition and keeping your body as habitable as possible —

or, to put it more scientifically, maintaining homeostasis.

So, apparently, it has to work extra hard while in space.

The dataset also confirmed that many astronauts' telomeres lengthen while in space,

but then shorten significantly when they come back to Earth — just like Scott Kelly's did in the Twins study.

The hypothesis for this is also...oxidative stress, problematic because

telomeres are essential for preventing damage to your chromosomes.

Not all of the changes were necessarily bad.

Scott Kelly experienced a decrease in blood cell mutations during his year in space.

Some astronauts exhibited increased levels of genetic tools that allowed them adapt slightly

to the effects of radiation and microgravity.

And this 2020 dataset also confirmed that astronaut gut microbiomes take on a unique profile while in space

(which I just think is super cool).

Overall, all of this gives us a much more robust picture of what goes on in the body while in space,

and what potential drugs or discoveries could make long-term spaceflight physiologically possible.

And as the astronaut core is only getting more diverse, scientists want to conduct more studies

with even more human participants on even longer spaceflights to make our understanding of bodies in space

as well-rounded as possible.

Because work like this doesn't just keep astronauts safe before and after their trips off-Earth —

it gives us even more insight into human health here on the planet too.

You can check out my previous video on the initial results of the NASA twin study here!

Make sure you subscribe to Seeker for all of your spaceflight news,

and if you have another topic you want us to cover in this area, let us know down in the comments below.

As always, thanks so much for watching, and I'll see ya next time.