Swimming in cold water could help to protect the human brain from dementia, a study involving users of the Hampstead Heath lido has suggested.

Researchers from the University of Cambridge believe a so-called “cold-shock” protein may hold the key to developing treatments that delay the onset of degenerative conditions. 

Production of the protein, known as RBM3, appeared to be triggered in mice when their body was cooled to the point of hypothermia and was found to subsequently help protect their brains.

It was more difficult, however, to establish whether this could be replicated in humans because ethical concerns about inducing hypothermia stood in the way of tests. 

When news of the impasse reached a group of swimmers who spend their winters in the unheated lido at Parliament Hill, London, they decided to volunteer their services to the researchers.

They pointed out that their body temperatures regularly reach the point of hypothermia during their favourite hobby and suggested they could be suitable subjects for a study. 

It followed that, during three winters between 2016 and 2018, a team of scientists tested the swimmers for the protein and found a significant level of RBM3 in many of them. 

Giovanna Mallucci, associate director of the UK Dementia Research Institute at the University of Cambridge, said “therapeutic hypothermia” was also used to protect the brain of patients and babies undergoing certain types of surgery.

“How cooling works is not entirely understood,” she told a recent virtual conference, where the findings were presented. 

“(Swimmers) get voluntary hypothermia, they swim in frozen water and we have worked with these people.

“We test RBM3 in human brains in patients having surgery and (we found) it does go up, it goes up in the babies and it goes up in the swimmers.

“The importance here is that we have a cold-shock response in humans that is like that in mice.”

The protein could potentially help with the treatment of conditions such as dementia by combating the destruction of synapses that take place in the early stages of the disease.

It was found in the 2015 study that mice without degenerative diseases could recover their synapses once they had returned from their hypothermic state, while those with the diseases could not.

The mice that recovered were found to have high levels of RBM3 which was not present in the other mice, suggesting the protein had a key role to play in the recovery. 

A subsequent experiment artificially boosted the levels of RBM3 in mice and found it could prevent the death of brain cells in the early stages of degenerative diseases. 

Prof Mallucci hopes the discovery of the protein in cold-water swimmers could help pave the way for treatments to be developed that use RBM3 to fight off degenerative conditions. 

The scientific breakthrough comes as cold-water swimming enjoys a boom in popularity in the UK, with growing numbers of people taking up the hobby during lockdown. 

The National Open Water Coaching Association (NOWCA), which promotes safe open water swimming, said there had been 110,000 individuals swims across the 40 venues it works with during this year’s summer season – a rise of 85 per cent on 2019.  

Chess Roffe Ridgard, an officer at NOWCA, said many of the cold-water swimmers she works with describe the “hugely” positive impact it has on their physical and mental health.

She said: “We have a lot of people who join us (in the winter) who have come out of the army with post-traumatic stress disorder, we have people with a history of self-harming – it can be very therapeutic.”

Some visitors to the open water venues say they have had it recommended by their doctor, while the mental health charity Mind has also championed the hobby, Ms Roffe Ridgard said. 

She cautioned, however, that new swimmers should make sure they are fully educated on how to stay safe while exercising in cold water as it induces a shock that can have a potentially extreme, and even fatal, reaction in the body.

NOWCA run inductions for cold water swimming online and at venues across the country. 

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