The circadian sleep–wake rhythm changes with aging, resulting in a more fragmented sleep–wake pattern. In individuals with intellectual disabilities (ID), brain structures regulating the sleep–wake rhythm might be affected. The aims of this study were to compare the sleep–wake rhythm of older adults with ID to that of older adults in the general population, and to investigate which factors are associated with the sleep–wake rhythm in older adults with ID.
This study is part of the ‘Healthy Aging and Intellectual Disabilities’ study (HA-ID). We applied actigraphy in 551 persons with ID and 58 persons in the general population, aged 50 years and over. Outcome measures were stability (interdaily stability), fragmentation (intradaily variability) and amplitude (relative amplitude) of the sleep–wake rhythm.
Compared to older adults in the general population, the sleep–wake rhythm of older adults with ID was significantly less stable (p = 0.03), more fragmented (p < 0.001) and had a lower relative amplitude (p < 0.001). Multivariate regression analysis revealed that higher age, dementia, depression, visual impairment, severe hearing impairment, epilepsy and spasticity are independently associated with a more disturbed sleep–wake rhythm in this group. The sleep–wake rhythm is more stable in females and those living at a setting for more intensive care. Higher physical activity levels are strongly associated with both a less fragmented (p < 0.001) and a more stable (p < 0.001) sleep–wake rhythm. Higher age, dementia and depression are also associated with the sleep–wake rhythm in the general population. Neurological and sensory impairments that were associated with the sleep–wake rhythm in older adults with ID, are frequent known conditions in the ID population. Further research should focus on which factors specifically influence the sleep–wake rhythm in older adults with ID, and on the effects of more physical daytime activity on the sleep–wake rhythm in this population.
The sleep–wake rhythm is a biological rhythm with duration of around 24 h (Sack et al., 2007). This circadian sleep–wake rhythm is controlled by the ‘circadian pacemaker’, a small group of cells located in the hypothalamus, called the suprachiasmatic nucleus (SCN) (Dijk & Lockley, 2002). Because the normal intrinsic circadian rhythm duration is slightly longer than 24 h (Czeisler et al., 1999), precise synchronization to a 24-h day mainly depends on exposure to environmental time signals, the so-called ‘Zeitgebers’, of which light is the most important one. A disrupted sleep–wake rhythm can lead to diminished quality of life, performance and health (Dijk & Lockley, 2002).
The SCN degenerates in the process of aging (Hofman & Swaab, 1994). As a result, older adults wake up earlier than younger adults, and their sleep becomes often more fragmented (van Someren, 2000). In patients with Alzheimer's disease, alterations of the sleep–wake rhythm might also be explained by decreased SCN function (Mirmiran et al., 1992). Besides SCN function, environmental factors and physical activity can affect the sleep–wake rhythm in older adults as well. van Someren, Lijzenga, Mirmiran, and Swaab (1997) observed that three months of fitness training led to a less fragmented rhythm in 10 healthy older men (van Someren et al., 1997). Meadows et al. (2010) studied the influence of residential status on the sleep–wake rhythm in 122 non-demented care-home residents and 52 community-dwelling poor sleepers. They observed that the care home residents had a more fragmented sleep–wake pattern than community-dwelling older adults, which could have been caused by ambient noise and light at night (Meadows et al., 2010). In older adults in the general population, depression is also associated with sleep–wake rhythm disturbances (Germain & Kupfer, 2008).
Because individuals with ID have some form of brain dysfunction, the circadian pacemaker in the SCN or pathways involved in the sleep–wake rhythm might be affected as well, besides the process of aging. Additionally, people with ID often live in groups with other clients, which might disturb the sleep–wake rhythm. As a result, the circadian sleep–wake rhythm in older adults with ID might be more affected than the sleep–wake rhythm of older adults in the general population.
To our knowledge, no studies have been published on the circadian sleep–wake rhythm of older adults with intellectual disability (ID). Therefore, the aims of this study were to compare the sleep–wake rhythm of this population with that of older adults in the general population, and to investigate factors related to the circadian sleep–wake rhythm in older adults with intellectual disabilities.
