He’s a retired astronaut who holds the current U.S. record for the longest ever single spaceflight,

clocking in at 342 consecutive days in space.

Some of you may also know that he has an identical twin...who is ALSO an astronaut.

What are the chances of that?!

Mark and Scott Kelly were the central figures in a brand new, totally unique twin study.

NASA just published the results that let us know, in unprecedented detail, what happens

to our bodies during long-term spaceflight—and we’re here to give you the rundown.

In the decades since first sending humans into space, we’ve been monitoring spaceflight-induced

physiological changes in hundreds of astronauts.

We can compare an individual to themselves before, during, and after a mission—allowing

NASA to develop countermeasures against issues like decreased bone density and decreased

muscle mass.

But so far, we’re most familiar with the results of 1-4 months of spaceflight, and

comparing an individual to themselves doesn’t clearly let us know what could be caused by

spaceflight vs. something that may have happened to that individual anyway.

If we’re expecting humans to survive years for something like transport to Mars, how

do we prep for that?

How do we know what’s going to happen to our bodies?

Well, Scott and Mark Kelly presented an incredibly exciting opportunity for NASA.

While Scott spent a year in space, Mark served as his ‘genetically matched ground control’.

Both twins were monitored closely before, throughout, and after the mission—physiologically,

genetically, and cognitively—creating a massive amount of data in the first twin study

of its kind.

Some things changed during spaceflight that, while SUPER interesting and important to keep

measuring in future studies, don’t seem to pose a significant health risk.

For example, body mass decreased, gut microbiome composition changed, and inflammation increased—all

temporarily.

Plus the flu vaccine works just as well on someone in space as it does for someone on

earth, which is a relief.

Then we’ve got the medium-risk stuff, stuff we may need to be careful about.

Urine sample metabolites indicated that spaceflight could interrupt collagen regulation in the

body.

While we may most often hear about collagen in the context of our skin, it’s also part

of all our veins and arteries and valves, and disturbance in its production and incorporation

could result in issues like blood pooling at the bottom of our legs or issues with blood

pressure regulation.

And don’t even get me started on the telomeres—these are the caps on the end of your chromosomes

that protect your DNA from damage and that deteriorate as we age.

Scott Kelly’s telomeres actually lengthened during his year on the ISS—but then shortened

rapidly and significantly when he returned to Earth.

They’ve since recovered to around pre-spaceflight length, but given the essential nature of

telomeres in protecting genomic integrity and the role we think they play in aging,

further research into this aspect of space-induced genetic changes could be really fruitful,

not only for spaceflight, but for other areas of science and medicine.

And now for the high-risk stuff, the stuff we really need to work on solutions for.

A comprehensive suite of computerized tests indicated that while some measures of cognitive

function increased, especially early in the mission, other cognitive functions—like

emotion recognition and abstract matching accuracy—actually declined during spaceflight,

along with cognitive speed.

And these declines persisted for about 6 months after return to Earth.

In a weightless environment, our veins and arteries can also get a little...confused.

Usually, they have to work with or against Earth’s gravity to move blood around our

body, but in microgravity, we see thickening of vascular walls, an increase in vascular

stiffness, and a ballooning effect in the vasculature of the upper body.

We’re actually still not sure if all of this is reversible after an astronaut comes

back to earth—that remains to be seen.

We also confirmed observations made in many other astronauts: spaceflight is associated

with altered optical function.

.We see swelling of the optical disc, a flattening of the actual globe of the eye, along with

other structural changes, which can lead to onset of blurry vision, blind spots, and more.

We haven’t been able to pinpoint what causes these changes but they’re obviously not

good for your eyesight, and may be permanent.

And lastly, blood samples pre-, during, and post- flight determined that spaceflight can

significantly increase genotoxic stress.

Space is highly radioactive, and while galactic cosmic rays may sound awesome, they can really

do a number on your DNA.

Cytogenetic analysis, which means looking at changes in your chromosomes, revealed higher

levels of genomic instability for the spaceflight twin.

This comes in the form of increased chromosomal translocations and inversions, which can be

linked to disorders like infertility and cancer.

Genetic analysis also revealed dysregulation of genes, especially those associated with

immune function and DNA repair, and these changes did not return to normal when they

got back to Earth.

All this talk of DNA changing may make it easy to ask the question, “Are they still

twins?”.

The answer is YES.

Media outlets a while back went a little overboard with the ‘news’ that 7% of Scott Kelly’s

DNA was different.

If 7% of Scott’s genes were completely different, not only would he not be Mark’s twin anymore,

he would be an entirely different species.

The real way to think about it is that yes, some genetic mutation occurred, but most of

the change was epigenetic change.

This means that something like DNA methylation, or a little add-on unit to a gene, changed

the expression of the gene, not the actual makeup of the DNA itself.

This can result in upregulation or downregulation of the genes in charge of things like immune

function and bone growth..So yeah.

They’re still related.

All of this data represents, as the researchers put it, “a uniquely controlled and integrated

framework for comprehensively quantifying astronaut biology in space”.

And opens up so many exciting questions that are going to be fascinating to build on.

Even though NASA doesn’t currently have any more twins in the pipeline, this kind

of research can continue with those who take on longer and longer spaceflights.

Building a better understanding of the effects of long-term spaceflight on the body and the

mind will prepare us to test even more spaceflight boundaries that no human has ever broken before—while

hopefully keeping us all in one piece.

We're working on a new series that we're stoked to share with you that's all about what goes

on in your body when you get sick.

And it’s called...well...Sick.

And here's our sneak peak of our first

episode

Beyond treatments and symptoms, we're curious about how exactly viruses, parasites, and

other invaders wreak havoc on our health.

Is there a disease or illness you want us to cover?

Let us know down in the comments and make sure you subscribe to catch the first episode.

Thanks for watching Seeker.