The team believes that the treatment works by changing the structure of vessels in the brain so that more blood can get through.
Professor Uri Ashery, of the Sackler School of Medicine, at Tel Aviv University, said: "We have discovered for the first time that hyperbaric oxygen therapy induces degradation and clearance of pre-existing amyloid plaques, and the appearance of newly formed plaques.
"Elderly patients suffering from significant memory loss at baseline revealed an increase in brain blood flow and improvement in cognitive performance, demonstrating hyperbaric oxygen therapy's potency to reverse core elements responsible for the development of Alzheimer's disease."
Although experts said the findings needed to be replicated in a larger trial and that such therapy may be difficult to offer at scale, they said it could open new doors in using oxygen therapy for the treatment of dementia.
"The paper presents an interesting approach, in particular reminding us of the importance of vascular factors in the development not only of vascular dementia but Alzheimer's disease too," said Tom Dening, professor of dementia research at the University of Nottingham.
Dr Richard Oakley, head of research at the Alzheimer's Society added: "Dementia is now the UK's biggest killer, with someone developing it every three minutes.
"Research is essential to improve care and find new treatments for the 850,000 people in the UK with dementia, set to reach 1.6 million by 2040."
Cure could lie in the air we breathe
For decades, scientists across the globe have struggled to find a drug that could prevent or reverse dementia, coming up with ever-more complex molecules to try to dampen the devastating impacts.
Yet the answer may be simpler than anyone thought: oxygen.
Tel Aviv University's study has shown that placing patients with Mild Cognitive Impairment in a hyperbaric chamber boosts blood flow in the brain, flooding vessels with oxygen and improving memory, attention and processing speed.
Many people diagnosed with MCI go on to develop Alzheimer's, so it may be the first treatment that could prevent such a decline.
Finding a therapy which could stop the disease in its tracks has never been more needed, as there are currently 850,000 people living with dementia in Britain, and the figure is expected to rise to one million by 2025.
Although the first drug for Alzheimer's – Aducanumab – was approved by the US earlier this year, there are fears it will not live up to expectations outside of clinical trials.
In contrast to a drug, hyperbaric therapy works by giving patients pure oxygen through a mask while inside a pressurised chamber. It is a similar high-pressure environment to that used to help divers to recover from the bends.
The pressure change allows more oxygen to be dissolved into the tissues and mimics a state of "hypoxia", or oxygen shortage, which is known to have regenerating effects.
Reduced blood flow to the brain, and the decrease in oxygen that it brings, is known to precede the onset of dementia and the level of flow directly correlates with the degree of cognitive impairment in Alzheimer's. So, it makes sense to think that improving blood flow might also improve the condition.
Improved memory and attention
In the new study, six elderly patients were given oxygen inside a chamber for 90 minutes, five days a week over the course of three months. The results showed that the blood flow in the brain had increased by 16 to 23 per cent.
At the same time, memory test scores improved by 16.5 per cent, attention by six per cent, and information processing speed was boosted by 10.3 per cent.
Researchers believe that treatment not only improves levels of oxygen in the brain, but actually changes the structure of blood vessels, increasing their width and reducing wall thickness. It suggests that the beneficial effects may last for some time after the treatment.
Testing on mice
Although the therapy has not yet been tested on patients with Alzheimer's disease, when scientists tried it on mice with Alzheimer's they found it reduced the number of amyloid plaques by up to 30 per cent, shrank remaining plaques by 18 per cent, and prevented the reemergence of new ones.
The sticky plaques are believed to prevent brain cells from communicating, and are one of the major targets in drugs for Alzheimer's.
The mice even started building better nests after the treatment, and navigated mazes more proficiently.
Professor Ashery said: "Elderly patients suffering from significant memory loss at baseline revealed an increase in brain blood flow and improvement in cognitive performance, demonstrating hyperbaric oxygen therapy's potency to reverse core elements responsible for the development of Alzheimer's disease."
In 2020, the same team showed that hyperbaric therapy can reverse the ageing process, lengthening telomeres (the protective carps at the end of chromosomes) by 20 per cent.
It also reduced senescent, or dormant, cells by up to 37 per cent, making way for new healthy cells to regrow.
As well as cognitive improvements, patients undergoing therapy have also reported improved physical abilities such as increased energy, stamina and even sexual performance, in men.
Few hospitals can offer hyperbaric treatment
However, there is a drawback. Few hospitals are able to offer hyperbaric treatment and the current therapy comes with a gruelling timetable of sessions.
"Presumably to be useful, the treatment would have to be continued indefinitely, so any patients would have to be very highly motivated and have good transport links to the treatment facility," said Professor Dening.
"If we consider that the number of people with dementia in the UK is approaching one million, it is hard to see how hyperbaric oxygen could ever be available on this scale.
"In short, it's an interesting idea but a long way off meeting the usual criteria to become a standard treatment."
But it does open a new avenue for treating the disease. Oxygen-delivering drugs are already in development for heart conditions and may also be useful for dementia.
"The paper presents an interesting approach, in particular reminding us of the importance of vascular factors in the development not only of vascular dementia but Alzheimer's disease too," added Dening.
Clinical trials needed
Alzheimer's charities said that further larger trials were needed to really know if the treatment is effective, but that therapies which prevent dementia in the first place may end up being the most useful.
Dr Susan Kohlhaas, director of research at Alzheimer's Research UK, said: "Many of the Alzheimer's treatments that are currently being tested are drugs that target the hallmark disease proteins directly, but it's important we maintain a broad spectrum of potential approaches.
"Larger scale clinical trials with many more people are needed to ascertain whether this treatment is effective, particularly when measuring longer term benefits to memory and thinking.
"We know the diseases that cause dementia begin in the brain many years before symptoms like memory loss show, and it's likely for treatments to be effective at slowing down the diseases that cause dementia, they need to be given earlier rather than later."
The Israeli study is part of a larger research programme looking to reverse ageing and its accompanying ailments, and the team say that further trials will take place shortly.
For now, the research is a tantalising glimpse that hope may be on the horizon for the treatment of Alzheimer's and that it may come from the most unlikely source - the air that we breathe.
