Perchance to sleep: ageing and circadian rhythm
Kirstie Anderson is Project Leader at Newcastle University’s Clinical Ageing Research Unit, for the ICICLE Sleep Study.
Sleep is a biological imperative, famously described as “of the brain, by the brain and for the brain.” In young and middle aged volunteers, sleep restriction can be shown to adversely affect memory formation, consolidation and mood. Sleep disorders including insomnia, obstructive sleep apnoea and restless legs all increase in prevalence with age but the effects of disturbed sleep in the oldest age groups are still poorly understood. Sleep becomes increasingly fragmented, although total sleep time does not change significantly and there is weakening of the circadian rhythm which is likely to be both biological and environmental.
We studied sleep and circadian rhythm using questionnaires and accelerometry in a large and carefully characterised UK cohort of 87-89 year olds. Few of those who were studied complained of significant sleep disturbance as assessed by questionnaire. This raises the possibility that some of the standard tools to assess disturbed sleep in a younger population, such as the Epworth Sleepiness Score and the Pittsburgh Sleep Quality Inventory might be less useful in an older population.
However, those participants who objectively reported that their sleep pattern was impaired were more likely to be cognitively impairment, disabled or depressed. They also had a higher prevalence of falls and arthritis.
Importantly those with the most disturbed sleep were less likely to survive to the end of the survey. There was a striking difference between participants who had very regular and consolidated sleep pattern and those who had little or no discernible sleep pattern.
Sleep as a modifiable risk factor for disease in the very old has been seen, not just in the Newcastle 85+ cohort but in several large US populations. Simple wrist accelerometry has proven a well-tolerated and cost efficient technique for screening populations. Sleep disorders remain under diagnosed but effective therapies are available across all age ranges. It remains to be seen whether intervention for sleep disturbance will have long term benefits of mental health and cognition in the very old but this is an area worthy of further study.