People who experience sleep disorders are at greater risk of developing dementia and other neurodegenerative conditions later in life, new research reveals.
In a new study, scientists at the UK Dementia Research Institute (UK DRI) at Cardiff University and the NIH Intramural Center for Alzheimer's and Related Dementias (CARD) in the US found that sleep disorder diagnosis made people up to twice as likely to develop a neurodegenerative disease in the 15 years that followed.
In one of the largest studies to date, the researchers examined the relationship between sleep and neurodegenerative disease using data from over 1 million electronic health records. They investigated whether disrupted sleep is an early sign of neurodegeneration or makes someone more likely to develop dementia later.
In the study, the scientists examined data from three biobanks: the Secure Anonymised Information Linkage (SAIL) databank, UK Biobank, and FinnGen. Across the three biobanks, they were able to obtain accurate, timestamped records of when people were experiencing sleep disorders, as marked in their medical records.
The team looked at people who had been diagnosed with one or more sleep disorders, which were grouped for data analysis into disorders associated with circadian rhythm, including narcolepsy, apnoea, hypersomnia (excessive daytime sleepiness), parasomnias (abnormal behaviours or movement during sleep - such as sleepwalking, night terrors), cataplexy, and 'non-organic' sleep disorders not linked to a known physiological condition, including generalised insomnia and nightmares.
Using large-scale statistical analysis methods, the scientists mapped out the relationships between the different neurodegenerative diseases and sleep disorders. Their findings included:
- For dementia (general diagnosis, specific disease not known), incidences of circadian sleep disorders and non-organic sleep disorders were associated with an increased risk of dementia in the 10-15 years that followed. The risk was further increased for people recorded as experiencing multiple sleep disorders.
- For Alzheimer's disease, circadian sleep disorders increased risk of Alzheimer's in the 10-15 years following sleep disorder diagnosis.
- For vascular dementia, circadian sleep disorders and non-organic sleep disorders increased risk of vascular dementia in the 5-10 years following sleep disorder diagnosis. The risk was further increased for people recorded as experiencing multiple sleep disorders.
- For Parkinson's, circadian sleep disorders and non-organic sleep disorders increased risk of Parkinson's in the 10-15 years following sleep disorder diagnosis.
The study also revealed that sleep disorders increased the risk of Alzheimer's and Parkinson's, independently of genetic risk. In people who had a low genetic risk, having a sleep disorder increased their overall risk. This suggests that sleep disorders and genetics are likely to be influencing risk separately, acting by independent mechanisms.
Dr Emily Simmonds, Bioinformatician at the UK Dementia Research Institute at Cardiff University, said:"In our study, we wanted to understand the complicated relationship between sleep and dementia. People living with dementia often experience sleep problems, but there is not yet enough evidence to say for sure whether poor sleep increases risk of dementia.
"We set out to see if we could figure out what order these things are happening. By using biobank data, we had timestamped records of when people had sleep disorders, and exactly when they were subsequently diagnosed with a neurodegenerative disease - rather than relying on self-reporting."
Our results are compelling, indicating a clear increased risk of neurodegenerative disease following a sleep disorder, across three large biobank datasets.
Through analysing over 1 million people's health records, we have found evidence to suggest that having a sleep disorder significantly increases someone's risk of going on to later develop a neurodegenerative disease.
Professor Valentina Escott-Price, Group Leader at the UK Dementia Research Institute at Cardiff University, said: "In fact, this increased risk was present for up to 15 years following a sleep disorder diagnosis, and the risk was even greater for people who experienced recurrent sleep disorders.
"Perhaps most interestingly, this increased risk was occurring independently of genetic risk factors for Alzheimer's and Parkinson's, with sleep disorders almost 'compensating' for low genetic risk. One would expect that if sleep disorders were caused by neurodegeneration, genetic risk of sleep disorder and neurodegenerative disease would line up. Further investigation is needed, but this points towards sleep disorders as a risk factor for these conditions."
In future research, the authors aim to factor the effect of medication into further analysis to examine whether improving sleep through the use of medication leads to a reduction in risk.
