During my last years in graduate school, I learned that the coolest experiment to ever be conduct was about to take flight – literally. In the genetics world, twin studies have been a classical tool used to study the nature vs. nurture effect of any given trait or disorder in humans. With the ever-increasing interest in understanding how long-term space travel affects humans, exploring this idea would obviously benefit from controlled twin studies, but what are the chances that NASA could actually find identical twins that are both qualified enough to be astronauts?
Turns out not as low as you would think!
Mark and Scott Kelly are twin brothers who joined NASA in 1996 and already had many spaceflights under their belts before the idea of a twin study even popped in to anyone’s head. However, in 2015, NASA jumped at their opportunity to perform what I think, is the coolest science experiment to have ever been executed. To get a better understanding of how being in space for an extended period of time, the NASA Twin Study would monitor an outstanding number of biological variables in both brothers before, during and after Scott’s 1-year long stay at the International Space Station, while Mark stayed on Earth.
While that alone makes for a pretty outstanding story, the best part of this experiment was truly how collaborative and integrative the studies were. The study was coordinated by NASA’s Human Research program, and over 84 researchers across 12 different universities performed the insane amount of work to analyze 10 different biological areas, including:
- Gene Expression
They knew they probably wouldn’t have a shot like this again and took advantage it. I was ecstatic in April when I saw the published results of the study since I’ve been following this experiment for years. Obviously, I was most interested in how cardiovascular function was impacted by long-term space travel. It’s been well known that the gravity-free environment of space takes some pressure of the heart from working so hard, but since the heart is a muscle, this lack of use causes a decrease in muscle mass. To combat this loss of muscle mass, astronauts typically spend ~ 2.5 hours exercising on the International Space Station! The heart also changes shape in space becoming more circular rather than elongated. Luckily, these changes return to normal once the astronaut returns to space, but what does spending a year in space do to your heart and vasculature? Here are the main cardiovascular changes from this study:
- Cardiac output increased by of 10% while moderate decreases in systolic and mean arterial pressure were observed (these findings are consistent with previous studies)
- The carotid intima-media thickness increased while Scott was in space and remained thicker 4 days after landing.
- Inflammatory cytokines and chemokines were increased during all spaceflight timepoints and returned to normal after landing.
- Urine levels of Collagen alpha-1(III) chain (COL3A1) and collagen alpha-1(I) chain (COL1A1) proteins were increased compared with preflight values, and these returned to baseline levels postflight.
- An increase in the ratio of plasma levels of apoliprotein B (APOB; a major constituent of LDL particles) to apolipoprotein A1 [APOA1; a major constituent of high-density lipoprotein (HDL) particles] during the last 6 months of the mission in space. This ratio came back to baseline once Scott returned to Earth.
One of the most important take-home messages is that many of the variables analyzed either stayed the same or returned back to baseline once Scott came back to Earth, suggesting the effects of being in space for a year, on the heart in particular, is temporary and reversible. Obviously, the results of this study are limited because only one set of twins was analyzed so it’s hard to definitively say that these results represent how a year in space affects all of us – but it gives great insight into the biological effects of long-term space travel.
While I only focused on the cardiovascular results here, this study has an insane amount of information that is definitely worth reading, particularly since there were some variables, such as telomere length and DNA damage that changed during Scott’s time in space, but never returned back to his normal levels. That SpaceX flight might not be the best idea *just* yet.
Christa Trexler, PhD is a postdoctoral fellow in the cardiology department at UC San Diego studying the mechanisms behind cardiac development and pathology. She is also one of the coordinators of the 500 Women Scientists San Diego Pod, which focuses on promoting equality and inclusivity while advocating for science in the community. You can follow her tweets @ChristaTrex