For example, one team found that the telomeres - the regions at the ends of chromosomes - in Scott Kelly's white blood cells got longer during the mission. Telomeres help protect chromosomes from deterioration, and they get shorter over the decades as people age.
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Scott's telomere lengthening "could be linked to increased exercise and reduced caloric intake during the mission," NASA officials wrote in a description of the newly announced findings.
"However, upon his return to Earth, they began to shorten again," the officials added. "Interestingly, telomerase activity (the enzyme that repairs the telomeres and lengthens them) increased in both twins in November, which may be related to a significant, stressful family event happening around that time."
Another research team found an apparent decrease in bone formation during the second half of Scott's space mission, and another group identified a slight decrease in cognitive ability (thinking speed and accuracy) shortly after he touched down. However, this latter trend is not substantial enough to suggest that the performance of Mars-bound astronauts will be appreciably affected, NASA officials said.