Basal Cortisol Levels Are Increased in Patients with Mild Cognitive Impairment: Role of Insomnia and Short Sleep Duration

Background: Mild cognitive impairment (MCI) is frequent in elderly and a risk factor for dementia. Both insomnia and increased cortisol levels are risk factors for MCI. Objective: We examined cross-sectionally whether increased cortisol levels are associated with short sleep duration (SSD) and/or the insomnia short sleep duration (ISS) phenotype, in elderly with MCI. Methods: One hundred twenty-four participants with MCI and 84 cognitively non-impaired controls (CNI)≥60 years underwent medical history, physical examination, neuropsychiatric evaluation, neuropsychological testing, 3-day actigraphy, assessment of subjective insomnia symptoms, and a single morning plasma cortisol level. The short sleep phenotypes were defined by sleep efficiency below the median of the entire sample (i.e.,≤81%) with at least one insomnia symptom (ISS) or without (SSD). ANOVA models were used to compare the various sleep phenotypes to those who did not present either short sleep or insomnia symptoms [non-insomnia (NI)]. Results: MCI participants had higher cortisol levels compared to the CNI group (p = 0.009). MCI participants with insomnia (n = 44) or SSD (n = 38) had higher cortisol levels compared to the NI group (n = 42; p = 0.014 and p = 0.045, respectively). Furthermore, MCI participants with ISS phenotype but not those with insomnia with normal sleep duration had higher cortisol levels compared to NI (p = 0.011 and p = 0.4, respectively). Both linear trend analyses showed that cortisol reached the highest levels in the ISS phenotype. Conclusion: The ISS and SSD phenotypes are associated with increased cortisol levels in elderly with MCI. Improving sleep quality and duration and decreasing cortisol levels may delay further cognitive decline.