| Most physiological processes follow predictable 24-hour patterns called circadian rhythms. Patients with dementia often have disrupted circadian rhythms which may be due to damage to the suprachiasmatic nucleus of the hypothalamus, the site of endogenous generation of rhythms. In addition, there is a reduction of environmental cues, and impairment in the ability of rhythms to synchronize to these cues, in patients with dementia. However, the health-related consequences of disturbed rhythms are unknown. The current study examined the relationships among dementia severity, rest/activity rhythms, and mortality. The subjects were 150 older adults (mean (SD) age of 84.1(7.8); 105 women, 45 men) with dementia residing in nursing homes in San Diego, CA. A diagnosis of dementia was determined from medical records and/or examination by a neurologist. Dementia severity was estimated with the Mini-Mental Status Examination (MMSE). Rest/activity rhythms were recorded using Actillume recorders and the data were modeled using an extended cosinor model that computes parameters to describe various characteristics of the rhythm. Public records were searched to determine if subjects had passed away since participating in the study. Death certificates were found for 121 subjects (81.2%), 9 subjects were confirmed to still be alive (6.0%) and 19 subjects were lost to follow-up (12.8%). The mean survival was 2.3 years (SD = 2.0; range = 0.3 to 10.4) after participating in the study. It was predicted that activity rhythms would be worse in patients with more severe dementia, and that disturbed rhythms would be predictive of shorter survival. In patients with weaker rhythms, MMSE was significantly related to rest/activity parameters such that subjects with more severe dementia had rhythms that were less robust (p = .009) and peaked later in the day (p = .019). Survival analyses revealed that the deviation of the acrophase (timing of the peak) from the that of a non-demented comparison group was significantly related to survival. Having an acrophase further from the comparison group was associated with shorter survival, regardless of the direction of the deviation. Interventions that improve rest/activity rhythms and adjust the timing of rhythms may lead to longer survival and better quality of life. |
