Sleep does not clear brain of toxins but exercise does, study finds

Setting an early alarm to go and work out at the gym may be better for your brain than a lie-in, it has emerged.

It has long been thought the brain uses sleep to flush out toxins and get rid of damaging molecules.

But a study now suggests the opposite may be true — and experts say being active might be more beneficial for “cleaning” our grey matter.

Researchers from Imperial College London’s UK Dementia Research Institute used a fluorescent dye to study the brains of mice — tracking how quickly the dye moved from one area of the brain to another before being cleared.

Analysis revealed the clearance of the dye was reduced by about 30 per cent in sleeping mice and 50 per cent in mice that were under anaesthetic compared with mice that were kept awake.

Although the findings need to be confirmed in humans, it casts doubt on the belief that sleep clears toxins via the glymphatic system, a mechanism that flushes waste from the brain.

Study co-lead author Professor Nick Franks said: “The field has been so focused on the clearance idea as one of the key reasons why we sleep, and we were very surprised to observe the opposite in our results.”

The researchers also said the size of molecules may affect how quickly certain toxins move through the brain, and some compounds are cleared through different systems.

Study co-leader Professor Bill Wisden added: “We have shown that brain clearance is highly efficient during the waking state. ‘In general, being awake, active and exercising may more efficiently clean the brain of toxins.”

The findings were published in the journal Nature Neuroscience.