As more is understood about how sleep affects our brain health, GPs are often the first port of call for worried people, explains researcher Dr Camilla Hoyos.
Growing evidence suggests disturbed sleep may increase the risk of developing dementia. Sleep optimises the ability of our brains to stabilise and consolidate newly learned information and memories. These processes can occur across all the different stages of sleep, with deep sleep (also known as Stage 3 or restorative sleep) playing a key role.
Furthermore, it is now known that the glymphatic system or the waste system of the brain is highly active during sleep, especially during deep sleep. This allows for waste products in our brains, including toxins, that have built up during the day to be cleaned out.
Toxins in the brain include beta-amyloid, one of the key proteins in the development of Alzheimer’s disease. Disturbing sleep could disrupt this cleansing process and lead to an accumulation of beta-amyloid in the brain.
The important role of sleep in these vital processes has led to the investigation of whether sleep disruption, including sleep disorders such as sleep apnoea, could be associated with changes in our cognition when we age and a possible link to the development of dementia.
Sleep apnoea is a common condition, estimated to affect one billion people worldwide. Sleep apnoea causes the upper airway to close either completely (an apnoea) or partially (a hypopnoea) during sleep.
These closures or obstructions can range from 10 seconds up to one minute and can lead to a drop in blood oxygen levels. To start breathing again, a short awakening occurs without the individual living with sleep apnoea being aware.
These closures may lead to drops in blood oxygen levels and fragmented sleep. The disruptions could impact the important processes in maintaining our brain health that occur during sleep.
Studies have shown sleep apnoea to be associated with a 26% increase in the development of cognitive impairment, as well as greater amounts of beta-amyloid in the brain. However, it is not clear if treating sleep apnoea can reduce this risk.
There are several treatments for sleep apnoea. The gold-standard is continuous positive airway pressure therapy (CPAP), where a mask connected to a pump blows continuous air down the upper airway keeping it open. It is not known whether treating sleep apnoea will reduce the risk of dementia.
Our recently published study aimed to understand if treating older adults with both sleep apnoea and mild cognitive impairment could improve thinking and memory skills in the short term. The trial assessed the effect of CPAP treatment on memory and thinking skills compared to no treatment. This was a cross-over study, which means all participants had both CPAP and no treatment during the trial.
Participants were randomised to the order in which they completed the two arms, meaning this process was done by chance and everyone had the same probability of using CPAP first. Participants were seen by trained staff to get established using the therapy. After using the treatment for three months, participants underwent a series of cognitive tests, and waited two weeks before starting the other study arm.
The researchers found that compared to not treating sleep apnoea, thinking skills were not improved with CPAP, whereas some improvements in memory were observed. This suggests treating sleep apnoea could potentially improve outcomes in the short term, but it is unknown if it would have any impact on long-term cognitive decline.
Mild cognitive impairment is the stage between the expected cognitive decline of normal ageing and the more serious decline of dementia. In mild cognitive impairment, cognitive changes are noticed by the individual and their family and friends, but the individual is still able to successfully carry out everyday activities.
Mild cognitive impairment is associated with an increased risk of developing dementia in subsequent years. Researchers believe this is the optimal time to intervene in an attempt to prevent a future dementia diagnosis.
This is where the role of the GP can be most useful. General practitioners may be best placed to observe early changes in cognition, especially if they have been seeing a patient for many years.
As GPs are already involved in assessing and managing people with other chronic diseases including asthma and diabetes, it would be beneficial if they were armed with greater information about sleep apnoea, namely how to identify and manage it, in collaboration with sleep specialists.
A previous study suggested CPAP could slow cognitive changes over one year in older adults with mild cognitive impairment and sleep apnoea.
However, studies of longer duration are needed before we can say what the long-term effects look like.
This is a space to watch for GPs, with further insights into the relationship between sleep and cognitive decline expected in the coming years.
ED: Dr Hoyos is a sleep researcher based at the Woolcock Institute for Medical Research.