Association of Objective and Subjective Sleep Duration and Diurnal Cortisol Rhythm among Community‐Dwelling People Living with Dementia

Abstract Background Evidence has shown that both short and long sleep duration have adverse effects on cognitive health in older adults. Although changes in sleep duration have been linked with alterations in the hypothalamic‐pituitary‐adrenal axis, research on the association between sleep duration and various components of diurnal cortisol rhythm is inconsistent. In addition, limited research has examined this association in community‐dwelling people living with dementia. The aim of this study is to examine the association of objective and subjective sleep duration and cortisol rhythm indicators in a community‐dwelling population living with dementia. Method Participants in the Healthy Patterns Sleep Study (NCT03682185) provided three saliva samples at wakening, 30 minutes after waking, and bedtime on two consecutive days. Diurnal cortisol rhythm indicators included waking cortisol, cortisol awaking response, diurnal cortisol slope, and bedtime cortisol. Objective sleep duration was measured by averaging actigraphy over three days, and subjective sleep duration was assessed by a single item from the Pittsburgh Sleep Quality Index. The average daily total sleep duration was grouped into three categories: ≤5 (short), ≥9 (long), and >5 & <9 (normal). 195 participants with valid cortisol and sleep data were used for analysis. Result Approximately 60% (objective) or 45% (subjective) of the participants maintained seven to eight hours of sleep. Normal and long objective and subjective sleep duration preserved an intact diurnal cortisol rhythm. Short objective sleep duration, however, was associated with higher waking cortisol (p = 0.016) and diminished cortisol awaking response (p = 0.049), compared to normal sleep. No significance was found using subjective short sleep duration. Conclusion This cross‐sectional study showed that objective short sleep duration was associated with disrupted cortisol rhythm. The findings suggest that neuroendocrine disturbance could be one mechanism linking sleep and dementia risk. Future studies are needed to confirm these findings using more sampling points in the morning. Additionally future research needs to consider the confounding sociodemographic and clinical characteristics such as race and dementia severity in a larger sample.