Aging of the population is associated with cognitive decline and several factors have been reported to be associated with Dementia. The objectives of our study were to explore the associations of several modifiable parameters, i.e. sleep, diet, and physical activity, with cognitive performance among community-dwelling elders from the island of Crete, Greece.

Our initial sample consisted of 3066 community-dwelling elders aged 60-100 years participating in the Cretan Aging Cohort. In Phase I, all participants were interviewed with a structured questionnaire assessing demographics, physical/mental health, life-style, sleep and subjective insomnia symptoms, as well as cognitive function using the Mini Mental State Examination (MMSE) test. The prevalence of one or more insomnia-type symptoms was 64.6%. Female gender, widowhood, benzodiazepine use and physical ailments were significantly associated with insomnia-type symptoms. Moreover, insomnia-type symptoms were associated with increased odds of cognitive impairment.

A sub-sample of the initial cohort including 550 participants was referred to Phase II of the study. Based on an extensive neuropsychiatric/ neuropsychological evaluation, participants were categorized as cognitively intact elders (NI), probable Alzheimer’s Disease (AD), or Mild Cognitive Impairment (MCI). Additionally, we assessed objective sleep using a 3-day 24h actigraphy, subjective sleep complaints, inflammation markers (i.e. TNFa, IL-6), diet patterns and physical activity.

In non-demented community-dwelling elderly, TNFa and IL-6 plasma levels were associated with long objective sleep duration, high carbohydrate and low vegetable/legume/fish diet, and physical inactivity.  

In addition, elderly patients with MCI had similar objective sleep duration with normal controls, while AD patients slept longer. Also, and interestingly, long sleep duration in patients with multi domain subtypes of MCI was associated with decrements in episodic memory and problem solving ability.

Furthermore, Dementia patients had more objective daytime sleepiness compared to NI. Also, within Dementia patients, those with daytime sleepiness had significantly worse cognitive performance. Finally, in patients with Dementia, IL-6 plasma levels were associated with increased daytime sleepiness.

In conclusion, (a) in elders insomnia-type symptoms are very prevalent and associated with increased risk for cognitive impairment, (b) combined interventions targeting several life-style parameters, i.e. sleep hygiene, healthier diet and physical activity, may decrease inflammation and improve or delay cognitive decline among elderly, (c) long sleep duration may be an early biologic marker of accelerated cognitive decline within multi domain subtypes of MCI, (d) in demented patients objective daytime sleepiness may be a biologic marker of the severity of the dementia.