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Usually seen in people with mid-to-late-stage dementia, sundown syndrome is the appearance of regular behavioural changes such as agitation and confusion around sunset.

A coastal sunset

Sundown syndrome (also referred to as sundowning) is an under-researched condition with no clear diagnostic criteria. Despite this, it is easily recognised by healthcare professionals due to its distinctive delirium-like symptoms which can include confusion, agitation, walking without purpose, disorientation, hallucinations, and aggression. What characterises sundown syndrome is that these behavioural changes occur each day for a few hours around sunset, when light levels are changing.

The key difference between sundowning and delirium – which leads to similar behaviour – is their duration. Delirium usually only lasts for a few months, when the person has a physical condition such as a urinary tract infection. By contrast, sundowning is a much longer-term phenomenon.

Although there are no established causes, risk factors or physiological explanations for sundown syndrome, the research points to a disruption in the body's natural clock. This clock is the suprachiasmatic nucleus (SCN) in the brain which dictates the daily and seasonal cyclic activities of the body. Specialised cells in the SCN receive information from the eyes about the light levels in the environment. The SCN responds to these signals by instructing the release of different hormones to control various bodily functions throughout the day, known as circadian rhythms.

It is thought that diseases like Alzheimer's damage the brain cells in the SCN, stopping it from responding appropriately to changing light levels. Therefore, when light levels drop at sunset, the dysfunctional SCN leads to distress and confusion.

However, this theory is yet to be scientifically proven, as most research on the subject is from caregivers' experiences of sundowning rather than controlled studies. The relationship between sundowning and dementia is currently unclear – does worsening dementia lead to sundowning, or does sundown syndrome cause or predict progression of dementia?

A review conducted in 2019 compiled the existing research into sundown syndrome. It concluded that studies using brain imaging techniques and psychological tests are needed to create diagnosis guidelines, identify biological signs of the condition, and increase the validity of existing knowledge.

Anecdotal reports suggest that fatigue, darkness, room changes and physical illness could all trigger sundowning. To avoid or reduce sundowning, groups like the Mayo Clinic and Healthline suggest the following things:

  • Adjusting the light levels in the environment can help prevent sunset triggering sundown syndrome. Putting a high, bright light on before the sun goes down avoids any sudden changes in brightness. It may also benefit someone to sleep with a night light so that they are never in total darkness.
  • Keeping the person at risk of sundowning active during the day can prevent them napping and struggling to sleep at night. For a similar reason, it is advisable to limit caffeine and sugar intake in the afternoon. A good night's sleep should reduce fatigue and can limit the occurrence of sundowning.
  • It's important to keep the environment as familiar and constant as possible. This can be done by establishing a consistent routine for eating, waking up and going to bed. It is also helpful to avoid making any drastic changes to the person's living conditions. For example, sundowning in care homes has been linked with the shift change in staff at the end of the working day. Altering shift patterns of staff so a whole team doesn't swap over at once can prevent the sudden change in the resident's environment.
  • It's also a good idea to monitor the person's behaviour over a period of time to identify anything that could be triggering their sundowning. Once you know potential individual causes of the behaviour, small adjustments can be made to help avoid them.

Advice like this can be very effective in supporting an individual who is experiencing sundown syndrome, but until the research catches up with the patient expertise, more concrete solutions will remain elusive. The key requirement is for more studies, using modern neuroscience techniques and large, wide samples of participants. Once this crucial research is under way, the mysteries of sundowning will begin to unravel.