One night of disturbed sleep increases levels of a brain protein linked to Alzheimer’s disease, research has shown.
A week of tossing and turning boosts another molecule implicated in the destruction of brain cells, the same study found.
Increasing evidence suggests an association between poor sleep and a greater risk of cognitive impairment or dementia.
The new findings published in the journal Brain show that just one bad night can affect a key signature of Alzheimer’s in the brain.
Lead scientist Professor David Holtzman, from Washington University School of Medicine in St Louis, US, said: “We showed that poor sleep is associated with higher levels of two Alzheimer’s-associated proteins.
“We think that perhaps chronic poor sleep during middle age may increase the risk of Alzheimer’s later in life.”
Brains of Alzheimer’s patients are clogged with accumulated deposits of a toxic protein called beta-amyloid. In addition, their neurons contain “tau tangles” – twisted knots of tau protein that disrupt nutrient transport within the cells and eventually kill them.
Experts believe both abnormalities contribute to Alzheimer’s disease and may be linked. One theory suggests that beta-amyloid acts as the “trigger” and tau as the “bullet” in a process that leads to the death of neurons.
Prof Holtzman’s team looked at 17 healthy adults aged 35 to 65 with no history of chronic sleep problems or mental impairments.
The volunteers agreed to spend a night in a specially designed, sound-proofed sleep room, while wearing headphones as their brain waves were monitored via electrodes attached to the scalp.
Half the participants were randomly assigned to have their slumber disrupted by beeps in their ears once their brain activity showed them to be in a deep dreamless phase of “slow-wave” sleep.
About a month later the process was repeated, but this time the two groups were reversed so that participants who previously had an undisturbed night were subjected to the beeps.
Tests on cerebrospinal fluid taken from the volunteers showed a 10% increase in beta-amyloid levels after a single night of interrupted sleep, but no increase in levels of tau.
However, participants who had slept poorly at home for a week before the spinal tap did display a spike in tau levels.