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Dementia and Sleep: How they are related

Dementia affects at least 55 million people worldwide and the number is increasing by about 10 million every year.

In Hong Kong, according to the Hospital Authority, the prevalence rates of dementia in Hong Kong is estimated to be at 5%-8% among persons aged over 65, and at 20%-30% among those aged over 80.

Causes of dementia

• Alzheimer’s Disease: Most common cause of dementia. Accounted for nearly 65% of dementia in Hong Kong Chinese elderly
• Vascular Dementia: 2nd common cause of dementia. Accounted for around 30% of dementia in Hong Kong Chinese elderly
• Others (Parkinson’s disease dementia, Hypothyroidism, Vitamin B12 deficiency etc.)

Several studies have shown the risk of dementia can be reduced by adopting a healthy diet, exercising regularly, and avoiding smoking and drinking too much alcohol.

One part of a healthy lifestyle is getting enough of the right sort of sleep. And many researchers are now seeing connections between sleep and dementia

“Sleep is a factor that can either be protective or risky for cognitive health. The effects of sleep on cognitive health depend on the attributes of an individual’s sleep, including the quality, quantity, frequency, and even the regularity of sleep.“ quoted from

How long should we sleep for?

The ideal and optimum quantity of sleep is between 7 and 9 hours

Sleep quality

four key features of quality sleep for optimum health benefits:

  • falling asleep within 30 minutes of going to bed
  • waking no more than once in the night
  • no more than 20 minutes awake during the night
  • spending at least 85% of your time in bed asleep.

Sleep apnea and dementia

Recent studies have also suggested links between sleep apnea and dementia. Another study found that the hippocampus was reduced in volume in people with sleep apnea — hippocampal atrophy is a feature of Alzheimer’s disease.

How does dementia affect sleep?

A study found that the daytime sleepiness is a sign of Alzheimer’s disease linked to the death of key brain cells. The researchers suggested this is due to a build-up of tau protein and loss of neurons in areas of the brain that promote wakefulness.

Cause or symptom?

The same study suggested that improving sleep might be a way of alleviating dementia symptoms, but is it possible that treating sleep disorders might help prevent dementia?

A 2019 review of studies into sleep disorders and cognitive decline tried to answer this question. It found that sleep disorders, including sleep apnea, insomnia, inadequate or overlong sleep, and sleep disturbance were linked to cognitive decline and dementia. However, no study has yet proved a causative link.


The information above contains general information about medical conditions and potential treatments. It is not medical advice. If you have any medical questions, please consult your doctor.