Daytime Sleepiness is Associated with Dementia and Cognitive Decline in Older Italian Adults. A population-based study

OBJECTIVE: The occurrence of dementia among the elderly has been associated with several, often not modifiable, risk factors. Recent epidemiological studies focused their interest on a possible association between cognitive decline and sleep, a potentially modifiable risk factor. Due to controversial results and limitations of the previous studies, we decided to reexamine the relationship between disturbed sleep and cognitive impairment in the elderly. METHODS: Seven hundred fifty subjects aged 65years or older were recruited. The Mini-Mental State Examination (MMSE) and the Global Deterioration Scale (GDS) scores were used to evaluate the severity of cognitive decline. Diagnosis of dementia was made by means of the DSM-IV criteria. The older adults were interviewed in order to assess the presence of several sleep complaints (insomnia, snoring and/or witnessed sleep apneas, restlessness and/or leg jerks, sleepwalking and nightmares). Excessive daytime sleepiness was evaluated by means of a validated questionnaire. The principal caregiver of each older adult took part in the interview, providing the information if the subject was unable to answer because of mental impairment. RESULTS: Eighty-six individuals were diagnosed as demented; a large part of them (47.8%), in particular, were recognized as being affected by Alzheimer's disease. The prevalence of each sleep complaint in the older adults was as follows: insomnia 84.7%, snoring and/or witnessed sleep apneas 26.2%, restlessness and/or jerks in the legs 25.7%, sleepwalking 0.5%, nightmares 6.4% and daytime somnolence 30.6%. Among sleep disturbances, excessive daytime sleepiness was independently associated with the presence of dementia in the elderly. In addition, the frequency of excessive daytime sleepiness increased progressively across the different categories of cognitive decline, as measured by means of MMSE and GDS scores. CONCLUSIONS: Insomnia, the most common sleep complaint in our sample, was not associated with the presence of cognitive decline. As opposed to insomnia, excessive daytime sleepiness was significantly related to dementia. Further studies are needed in order to investigate the direction of this association and to evaluate the possible role of daytime somnolence as an early marker of neurodegenerative disease, particularly Alzheimer's disease, in some older adults.