The average person sleeps for about a third of their life. There must be something really important about sleeping - but just what is sleep good for?

One approach scientists take to understand why sleep is so important is to prevent animals sleeping for long periods of time. But this is challenging because sleep deprivation promotes “rebound sleep” – the powerful urge to sleep that hits you after an all-nighter. So, the authors of a recent study, published in the journal Cell, devised an ingenious method to bypass rebound sleep in fruit flies: they activated specific neurons in the flies' brains to keep them awake.

The researchers discovered that preventing these flies from sleeping by manipulating these neurons caused death after 10-15 days. Then they tackled the question of where in the body one might see changes or damage after 10 days of sleep deprivation? Surprisingly, they did not find any obvious changes in the brain. Instead, sleep deprivation caused a huge buildup of specific toxins, called “reactive oxygen species” (ROS) in the flies' guts. ROS are a normal byproduct of cell activity, but excessive ROS production causes cell damage. The scientists discovered damage throughout the flies' guts due to ROS accumulation.

Now they knew that sleep deprivation caused gut damage. But did it prematurely kill the flies? To test this, the researchers fed flies a variety of antioxidants, substances which protect against ROS. Adding these antioxidants to flies’ diets didn’t reduce sleep loss, but it did prevent the accumulation of ROS in the intestine. Crucially, it allowed flies to survive as long as they usually would despite the loss of sleep. In fact, by expressing enzymes that break down ROS just within cells of the gut, the authors were able to protect flies from death by sleep deprivation.

This study suggests that one essential function of sleep might be to prevent damage to the gut. How sleep loss causes ROS buildup remains unclear. But the authors show that similar damage occurs in the intestines of mice when they lose sleep – indicating that sleep may protect the guts of many species, not just flies. In the modern world, many of us live with chronic insufficient sleep, and it remains to be seen how this affects the health of our guts. But perhaps the next time your eyes start to droop, you will think of your gut and head to bed!