Self-reporting sleep quality may underestimate sleep problems in dementia, study finds

People with cognitive impairment due to Alzheimer’s disease or Lewy body disease may underestimate how disturbed their sleep is when asked to report it themselves. This sleep discrepancy (the gap between how well participants thought they slept and how they slept according to objective measurements) could have broader diagnostic value, according to research published in Alzheimer’s & Dementia.

The study compared subjective sleep reports with objective sleep data collected using wrist-worn actigraphy over 8 weeks. It included 20 people with mild cognitive impairment or mild dementia due to Alzheimer’s disease or Lewy body disease, alongside 20 cognitively healthy older adults.

The findings suggest that questionnaires alone may not give a reliable picture of sleep in memory clinic populations. Participants with Alzheimer’s disease and Lewy body disease generally reported better sleep than was recorded by wearable devices. On average, they described sleeping for around 7 to 8 hours a night, while actigraphy suggested they were getting closer to 6 hours.

Alzheimer’s disease and Lewy body disease are progressive neurodegenerative diseases which cause dementia. Dementia is a general term describing the loss of memory and other cognitive abilities serious enough to interfere with daily life. Alzheimer’s disease is more common than Lewy body disease.

The researchers found important differences between these groups. People with Alzheimer’s disease tended to report satisfaction with their sleep, while those with Lewy body disease reported poorer sleep quality. However, both groups showed a gap between perceived and objectively measured sleep. This suggests that self-report and wearable data capture related but distinct aspects of sleep health.

Victoria Gabb, joint first author and clinical researcher at Bristol Medical School and NIHR BRC: Bristol, said:

“Our findings show that we need to mind the gap between how people feel and report they sleep and what objective measures show us.

“Sleep questionnaires remain important because they tell us about someone’s experience of their sleep, but they should not be used as a substitute for objective measures in people with cognitive impairment.”

Researchers were able to distinguish between the Alzheimer’s disease, Lewy body disease and healthy control groups with promising accuracy by combining subjective sleep quality reports with discrepancies in:

• Sleep duration
• Sleep latency (the time it takes to fall asleep)
• Sleep efficiency (the proportion of time in bed that you actually spend asleep)

The authors say this raises the possibility that sleep discrepancy could support future diagnostic assessment, although larger and more diverse studies are needed before it could be used clinically.

The study also highlights the potential value of routine sleep screening in memory clinics. Sleep disturbance is increasingly recognised as both a symptom and possible risk factor for dementia, but it is not routinely assessed in many services. The researchers recommend that future dementia research and clinical assessment should collect both subjective and objective sleep measures, rather than treating one as a proxy for the other.