Inhaling high levels of carbon dioxide intermittently for half an hour flushes proteins linked to Alzheimer’s disease out of the brain, a small study has found. Exposure to the gas changes how blood vessels in the brain constrict and dilate while we’re awake, mimicking activity that occurs during deep sleep. This then turbocharges the glymphatic system to remove the build-up of waste products that could cause harm.
A 2025 suggests the same approach could help with Parkinson’s disease, by clearing the protein alpha-synuclein. “If you have any condition that is due to or exacerbated by any sort of accumulation of waste, this could be something beneficial,” says at the University of Texas at Austin.
The brain’s waste-disposal, or glymphatic, system is comprised of a network of channels surrounding blood vessels that collect waste fluid released from brain cells. It is most active during deep sleep, when slow brain waves drive blood vessels to dilate and constrict about once every 30 seconds.
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“This dilation and constriction essentially serves as a pump that clears waste from the brain,” says Ryman, who presented the results last week at the in London.
To mimic this pumping while people are awake, Ryman and her colleagues made use of the fact that breathing raised levels of carbon dioxide causes blood vessels to temporarily dilate, as the body tries harder to get rid of the gas and supply more oxygen to tissues.
The team recruited 12 people, of whom eight had no signs of cognitive impairment and normal levels of tau, a protein that can misfold and form tangles in Alzheimer’s disease. The four other participants had elevated levels of a form of tau in their blood, suggesting high levels in their brain, and three had mild cognitive impairment.
All the participants had their brains scanned while wearing a mask that switched between delivering air made up of about 0.05 per cent carbon dioxide – like the amount we inhale with every breath – to 5 per cent carbon dioxide. This switch happened every 35 seconds for half an hour.
The researchers found that intermittent exposure to high carbon dioxide levels caused the brain’s blood vessels to pump as they do during deep sleep, driving the glymphatic system.
The team also collected blood samples before and after the half-hour session. Fifteen minutes later, levels of a form of the protein called beta-amyloid – which is similarly found in healthy brains but forms clumps during Alzheimer’s disease – had increased in the blood of all the participants. “This suggests this neurodegenerative marker was being cleared more out of the brain,” says Ryman.
The intervention also seemed to boost the clearance of tau, but only among those with signs of cognitive decline. This may be because this group had more tau in their brains in the first place, says Ryman.
But an around an hour after the intervention ended, the amyloid and tau-clearing benefits had returned to baseline. Further studies need to explore whether this has an impact on Alzheimer’s disease risk or progression in the long-term, and how often you’d need to do it, says at Changi General Hospital in Singapore.
“We just don’t know yet whether targeting clearance with an approach like this really is going to affect cognitive decline,” says at the University of Washington in Seattle. “The interesting thing though is that stimulating these [glymphatic] clearance mechanisms is not specific to amyloid, but it can help clear amyloid, tau, alpha-synuclein and inflammatory molecules, so you could imagine the approach could have a much wider effect on the brain, and could have a much broader application that transcends Alzheimer’s disease.”
Safety also needs to be monitored long-term, although none of the participants experienced any side effects. The researchers could also explore delivering the intervention via a portable device at home, says Ryman. This may be preferable to existing ways of boosting the glymphatic system, which typically involve drugs, she says.
