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It seems strange that animals, us included, spend so much time vulnerably curled up with their eyes shut, totally unaware of our surroundings. While we might aim to get a solid eight hours in, giant armadillos sleep for 18 hours a day, while koalas snooze for an impressive 22 hours. So why did this bizarre behavior – which turns an alert animal into easy prey – evolve?
Sleep has all sorts of benefits, from reducing stress and improving your memory to reducing your risk of heart disease. Now, scientists at Bar-Ilan University in Israel have uncovered yet another crucial benefit of getting some Zs – it helps your body repair damaged DNA.
To conduct their study, the team turned to zebrafish, animals that make surprisingly good model organisms as their young are transparent, allowing scientists to peer inside. The researchers genetically engineered zebrafish so that their chromosomes – DNA-containing structures – were tagged with colored chemicals. They then examined their neurons under a microscope, studying the chromosomes and DNA within them, and compared what they saw when the fish were asleep and awake.
Publishing their findings in Nature Communications, the team found that during the day, DNA damage built up and the chromosomes weren’t very active. But during the night, the opposite occurred – DNA damage plummeted, and the chromosomes changed shape much more often than they did when the fish were awake. This shape-shifting boosts DNA repair mechanisms.
“It’s surprising, because the brain goes into a rest state, but the chromosomes move about twice as much during sleep,” lead researcher Professor Lior Appelbaum told The Guardian. “There is repair going on in the day, but sleep allows you to catch up.”
Therefore, it seems that sleep gives our neurons a chance to fix damaged DNA very efficiently, something that can’t be achieved while we’re awake as our brains are too active.
"It's like potholes in the road," Appelbaum explained in a statement. "Roads accumulate wear and tear, especially during daytime rush hours, and it is most convenient and efficient to fix them at night, when there is light traffic."
The research shows that sleep has essential health benefits right down to the cellular level, adding to the pile of evidence that suggests not getting enough shut-eye can have worrying impacts on your health. A build-up of damaged DNA in the brain can lead to neurodegeneration, a process implicated in a range of diseases such as Alzheimer's and Parkinson's, so getting enough sleep is definitely a good idea.
"Despite the risk of reduced awareness to the environment, animals – ranging from jellyfish to zebrafish to humans – have to sleep to allow their neurons to perform efficient DNA maintenance, and this is possibly the reason why sleep has evolved and is so conserved in the animal kingdom," Appelbaum said.
