People with dementia often have issues with sleep with their memory seemingly worse after a bad night. However, the evidence is unclear on whether poor sleep is a risk factor for dementia.

The relationship between dementia and sleep

Sleep and dementia is a complicated topic. Different types of dementia are associated with different sleep problems. Researchers are also not yet sure which way the interaction goes - whether poor sleep causes or exacerbates dementia or if dementia leads to poor sleep. Some researchers believe that both of these theories could be true, and the relationship could be circular.

On top of this, it is unclear what the mechanisms are that underlie these interactions. It is clear that more research is needed to understand this relationship; in particular research that observes large groups of affected people for very long periods of time.

Different types of sleep disorders

What are light sleep disorders?

Light sleep disorders are often called rapid eye movement sleep behaviour disorder (RBD), and cause people to act out their dreams through moving or talking in their sleep.

Dementia with Lewy bodies and Parkinson's disease seem to be particularly associated with light sleep disorders and some studies have suggested that light sleep disorders are a very early indicator of these conditions, particularly in older men.

Some researchers believe that the part of the brain that is damaged with dementia with Lewy bodies or Parkinson's disease also plays a role in light sleep, explaining why people with these conditions are particularly affected by light sleep disorders.

What are sleep-wake cycle disorders?

The sleep-wake cycle is the 24 hour cycle that the body goes through each day, normally ensuring that we are active during the day and sleepy at night. When this cycle is altered is causes many unusual and disruptive sleep patterns. These include wakefulness at night and problems falling asleep and staying asleep, as well as drowsiness and napping during the day.

These sorts of sleep disturbances are associated with many kinds of dementia, most notably Alzheimer's disease. They also affect people with Parkinson's disease.

It is thought by some researchers that the Alzheimer's hallmark protein amyloid may be behind the link between Alzheimer's disease and sleep-wake cycles. Increased amyloid in the brain is commonly seen in people with Alzheimer's and studies have shown that raised amyloid levels may be associated with poor sleep quality.  The amyloid protein has also been linked to problems with storing memories whilst we sleep and other research indicates that poor sleep may affect the body's ability to clear the toxic amyloid protein from the brain. 

This has led to the suggestion that improving sleep quality may have the potential to delay progression of Alzheimer's. However, it is also possible that the changes to the sleep-wake cycle are caused by other changes in the brain, and do not have an impact on risk of Alzheimer's. More research is needed to understand what the mechanisms linking sleep-wake cycles and Alzheimer's are.

What is sleep disordered breathing?

Sleep disordered breathing is when someone has difficulty breathing when they are asleep. This may be because of obstructions to the airway, making breathing harder work. Sleep disordered breathing is sometimes called sleep apnoea.

People of all ages can be affected by sleep disordered breathing, but it is most common in older people and people with obesity. Some research has suggested that people who are affected by sleep disordered breathing may be at higher risk of cognitive decline or impairment. This is because sleep disordered breathing may cause damage to the brain due to changes of levels of oxygen and carbon dioxide in the blood. It may also change flow of blood to the brain. 

Treatments for poor sleep

Good quality sleep is linked to good health, including cognitive health. Researchers have also investigated whether there are effective treatments for poor sleep and whether these treatments can affect dementia risk. Some drug treatments for poor sleep, such as benzodiazepines, have been linked to an increased risk of dementia although the evidence behind this link is conflicting. 

Many treatments that have been suggested to improve quality of sleep involve lifestyle changes. Regular sleep regimes, eating schedules and diets, exercise, and ensuring exposure to bright light in the morning are all ways that you can improve your sleep quality. However more research is needed to indicate whether these activities have an effect on risk of dementia or disease progression. 

A machine called continuous positive airway pressure (CPAP) has been shown to reduce the consequences of sleep apnoea by several studies. Before this treatment can be used, research is needed to indicate with more detail how to use it, for example how long the treatment should last and what lifestyle changes can be made to help.

There are also several drugs that have been trialled to improve sleep. Some doctors may prescribe melatonin, a hormone believed to be important in maintaining regular sleep-wake cycles. There is some evidence that this treatment does improve sleep quality in people with Alzheimer's disease and Parkinson's disease but so far evidence suggests melatonin does not affect risk of dementia or cognitive function.