Apnoea or habitual long sleep doubles AD risk

Having sleep apnoea or sleeping more than 9 hours every night doubles the risk of developing Alzheimer’s disease (AD) in middle-aged individuals within 6 years in a new study.

“Addressing sleep problems in middle-age may then play a role in improving brain health,” said lead author Dr Lei Gao from Harvard Medical School and Brigham and Women’s Hospital in Boston, Massachusetts, US, who presented the results at AAIC 2020.

The study had over 500,000 individuals from the UK Biobank (mean age, 57 years). They had no AD at baseline and followed for up to 12 years. Self-reports of sleep traits, sleep apnoea diagnosis, and day/night sleep duration were looked into. AD diagnoses were determined from hospital admissions and death registries.

Over a mean follow-up of 6.4 years, 932 individuals developed AD.

Compared with those getting 6–9 hours of sleep every night, those getting more than 9 hours of sleep habitually had a higher risk for AD (hazard ratio [HR], 2.04; p<0.0001). Sleep apnoea also increased AD risk significantly (HR, 2.05; p=0.006) in the core model, so was daytime sleepiness (HR, 1.56; p=0.001). [AAIC 2020, abstract ODO44575]

After controlling for sleep duration, sleep apnoea and daytime sleepiness remained predictive of AD. “All three sleep traits were associated with AD within the same model, suggesting some degree of independence,” Gao said. “And interestingly, we’ve found no link between snoring,  which is a common symptom of sleep apnoea, and AD risk in our study.”

He described sleep apnoea as a complex, multisystemic sleep disorder associated with obesity, high blood pressure, and often other heart problems. Given patients’ increased risk for airway difficulties, adverse cardiac events, post-op complications, and confusion or delirium, which is also associated with higher risk for eventual AD and death, Gao said these are the profile of patients he would deal with extreme caution as an anaesthesiologist.

The  above multisystemic factors may be driving the link to AD, hence “we need to address this better as the population ages and obesity rates increase,” he emphasized.

Although Gao and his team tried to control for comorbidities and medication use, a reverse causation could be at work. Sleeping too much, for example, could be both a cause and a symptom of dementia, he said. In fact, daytime sleepiness and sleeping too long may be a result of preclinical AD.

More work examining objective measures of sleep duration and sleep disturbance within this population is ongoing and may help to confirm the findings. Whether there is a reverse causation or not, Gao said there might be a “significant window of time to intervene,” considering that the average time to AD diagnosis was over 6 years in the study.

His best advice to improve sleep health? Sleep and wake up at similar times daily, stay away from coffee and alcohol close to bedtime, and reduce screen exposure if possible, among other do’s and don’ts.

And lastly, have sleep apnoea treated. “Addressing the pauses in breathing and the apnoea episodes will help reduce cardiovascular health risks,” Gao concluded.