Twin brothers. One went into space. The other didn't. NASA reveals how their bodies differ

As it prepares for interplanetary missions, NASA is offering a glimpse of its study of the effects of space on twins.

Twins have intrigued scientists for millennia and have been used to study genetics, behavior, biology, and psychology, among other areas of research, for good and for ill. They provide an experimental subject and a control subject, such that biological differences between the two are minimized.

Being in space is harmful to the human body and NASA needs to better understand the potential risks astronauts could face traveling to Mars or elsewhere.

A week ago, in Galveston, Texas, NASA presented early research results from the Twins Study at its Human Research Program's annual Investigator's Workshop.

The study features Scott Kelly and Mark Kelly, who are identical twins, but for a mustache.

NASA astronaut Scott Kelly returned to Earth last March after a year in space. His identical twin brother Mark, who retired from NASA in 2011, remained on Earth during that time, affording NASA scientists the opportunity to compare the biological effects of Scott Kelly's time in orbit with his brother's time on Earth.

One preliminary finding suggests a link between being in space and inflammation, known to play a role in human diseases. Investigator Mike Snyder found altered levels of lipids in Scott that signify inflammation.

His ground-bound brother Mark, meanwhile, was found to have a greater level of a metabolite called 3‑indolepropionic acid (IPA) that helps maintain normal insulin activity and is being studied as a way to mitigate the effects of Alzheimer's Disease.

Researcher Susan Bailey found that Scott's telomeres, specifically on his white blood cells, lengthened while he was in space. Telomeres, caps at the end of chromosomes that protect them, normally shorten as we age, though healthy behavior can slow that process.

As appealing as it may be to jump to the conclusion that time in space might lengthen lifespans, NASA suggests the finding may be a consequence of increased exercise and decreased caloric intake, both of which are known to play a role in health and longevity. In any event, Scott's telomeres began to shorten again when he returned to Earth.

Data collected by researcher Mathias Basner suggests that returning to Earth after a one-year mission produces a slight decrease in the speed and accuracy of cognitive function, compared to being away from Earth for only six months.

Also, the viral, bacterial, and fungal microbiome of the two twins differed, as might be expected, because their diets and environments differed. How this difference might affect an astronaut's health for a long period of time has yet to be explored.

NASA said it plans to issue a more detailed report later this year, followed by articles from the various researchers participating in the project. The space agency hopes to be able to send humans to Mars in the 2030s. ®