INTRODUCTION: Growing evidence suggests that impairment in rest-activity rhythms may be a risk factor for cognitive decline and impairment in the aging population. However, previous studies included only a limited set of rest-activity metrics and produced mixed findings. We studied a comprehensive set of parametric and nonparametric characteristics of rest-activity rhythms in relation to mild cognitive impairment (MCI) and probable dementia in a cohort of older women. METHODS: The prospective analysis included 763 women enrolled in two ancillary studies of the Womens Health Initiative (WHI): the WHI Memory Study-Epidemiology of Cognitive Health Outcomes and Objective Physical Activity and Cardiovascular Health studies. The association between accelerometry-based rest-activity parameters and centrally adjudicated MCI and probable dementia were determined using Cox regression models adjusted for sociodemographic characteristics, lifestyle factors, and comorbidities. RESULTS: Overall, the results support a prospective association between weakened rest-activity rhythms (e.g., reduced amplitude and overall rhythmicity) and adverse cognitive outcomes. Specifically, reduced overall rhythmicity (pseudo F statistic), lower amplitude and activity level (amplitude/relative amplitude, mesor, and activity level during active periods of the day [M10]), and later activity timing (acrophase and midpoint of M10) were associated with a higher risk for MCI and probable dementia. Women with lower amplitude and mesor also exhibited faster cognitive decline over follow-up. CONCLUSION: Weakened rest-activity rhythms may be predictive markers for cognitive decline, MCI, and dementia among older women.

Altered 24-hour rest-activity rhythms may be associated with cognitive impairment in older adults, but evidence from prospective studies is limited. Nonparametric methods were used to assess actigraphy-based activity patterns in 2 496 older men. Incident cognitive impairment was assessed 4 times over 12 years using the Modified Mini-Mental State Examination (3MS) and Trails B tests, self-reported medication use, and clinical diagnosis. The highest quartile (vs the lowest) of intradaily variability and the lowest quartiles (vs the highest) of interdaily stability and relative amplitude were associated with incident cognitive impairment (hazard ratio [95% confidence interval]: 1.82 [1.31-2.53], 1.36 [0.99-1.86], and 1.85 [1.33-2.56], respectively). A larger increase in intradaily variability over 7.5 years was associated with a greater subsequent decline in 3MS scores but not in Trails B performance. In conclusion, less stable and more variable rest-activity rhythms may represent early biomarkers of cognitive impairment in older men.