NASA took advantage of the unique opportunity of having a set of twin brothers as astronauts by studying each to take a closer look at the effects on the human body after spending a year in space.

For those in the dark on the U.S. space agency's study, astronaut Scott Kelly and his twin brother, Mark Kelly, took part in NASA's "Twin Study." The study looked at what a year in space did to Scott Kelly while Mark Kelly spent the year on Earth.

"By measuring large numbers of metabolites, cytokines, and proteins, researchers learned that spaceflight is associated with oxygen deprivation stress, increased inflammation, and dramatic nutrient shifts that affect gene expression," NASA reports in its preliminary findings.

"After returning to Earth, Scott started the process of readapting to Earth's gravity. Most of the biological changes he experienced in space quickly returned to nearly his preflight status. Some changes returned to baseline within hours or days of landing, while a few persisted after six months."

NASA clarifies in the report 93 percent of Scott Kelly's genes returned to normal after he came home, but that the missing 7 percent points "to possible longer-term changes in genes related to his immune system, DNA repair, bone formation networks, hypoxia, and hypercapnia."

The space agency reports that Scott Kelly's telomeres became longer while he was in space. Telomeres are chromosomes that shorten as a person ages, so that's why that change is such a noteworthy finding.

A typical mission to the International Space Station usually only lasts six months, and NASA says that increasing Scott Kelly's stay to one year "resulted in no significant" changes when it came to his cognitive performance. This mission comes at a valuable time as an increased in manned-missions to the moon, Mars and beyond could take much longer to complete. A mission to Mars, as Newsweek notes, could take as long as three years.

1st results of @NASA's Twin Studies w myself & @ShuttleCDRKelly are out. Turns out we are related! But there's more: https://t.co/Ov8zV995QR pic.twitter.com/hfAG2s6MMw — Scott Kelly (@StationCDRKelly) January 28, 2017

The space agency says there was "a more pronounced decrease' in his speed and accuracy after he landed, but chalked that up to adjusting to Earth's gravity and his busy schedule upon return.

The U.S. space agency's Twins Study represented a partnership between 10 individual investigations, 12 colleges and universities, NASA's biomedical labs and the National Space Biomedical Research Institute Consortium.