Sleep has critical roles in health and regeneration, and one of those is clearing the brain of metabolic waste, according to researchers from the US and Denmark.

Now, as reported in the journal Nature Communications, they’ve discovered in mice that the time of day matters, suggesting the process is controlled by circadian rhythms.

“Our group has shown that just being awake or asleep drastically changes how well the brain can clear waste,” says lead author Lauren Hablitz from the University of Rochester Medical Centre.