Sleep does NOT flush the brain of toxins

It’s always such a relief to get into bed at the end of a long day.

But exactly why humans need to sleep remains a mystery, according to new research.

It has long been thought that the brain uses sleep to eliminate toxins and get rid of harmful molecules.

However, a new study suggests the opposite might be true – and experts say being active could be more beneficial for ‘cleaning’ the brain.

A team from the UK’s Institute of Dementia Research at Imperial College London used a fluorescent dye to study mouse brains, tracking how quickly the dye moved from one area of ​​the brain to another before finally being eliminated.

They found that fluid clearance and movement were markedly reduced during sleep and under anesthesia.

The analysis revealed that clearance of the dye was reduced by approximately 30% in sleeping mice and 50% in anesthetized mice, compared to mice kept awake.

Although these findings have yet to be confirmed in humans, they challenge the long-held belief that sleep removes toxins via the glymphatic system, a mechanism that removes waste from the brain.

Previous research has suggested that sleep is important for preventing dementia because it is during this time that toxic proteins are cleared from the brain.

Study co-senior author Nick Franks, professor of biophysics and anesthesia at Imperial College London, said: “The field has focused so much on the idea of ​​clearance as one of the main reasons why we sleep, and we were of course very surprised to observe the opposite in our results.

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The researchers also said that molecule size can affect how quickly certain toxins move through the brain and that certain compounds are cleared by different systems.

“At the moment, we don’t know what in these states slows the elimination of molecules from the brain,” added Professor Franks.

“The next step in our research will be to try to understand why this happens.”

Study co-leader Professor Bill Wisden, interim director of the UKDRI centre, said: “There are many theories about why we sleep, and although we have shown that elimination of toxins may not be a key reason, it cannot be disputed that sleep is important.

“Sleep disturbances are a common symptom in people with dementia. However, we still do not know whether this is a consequence or a determining factor in the progression of the disease.

“It may well be that getting good sleep helps reduce the risk of dementia for reasons other than eliminating toxins.”

“The other aspect of our study is that we showed that brain cleaning is very effective in the waking state.”

“In general, being awake, active, and exercising can more effectively cleanse the brain of toxins.”

The results were published in the journal Nature Neuroscience.