Counting Zs: Determining the Monitoring Days Needed to Obtain Reliable Sleep Metrics in Older Adults with Mild Cognitive Impairment.

OBJECTIVE

This study aims to determine the minimum number of days required to obtain reliable actigraphy-measured sleep metrics in older adults with Mild Cognitive Impairment (MCI).

METHODS

One hundred and fourteen older adults (61 with MCI, 53 cognitively unimpaired) wore wrist-worn actigraphy devices for at least 60 days. Total sleep time (TST), sleep efficiency (SE), and wake after sleep onset (WASO) were calculated over cumulative windows (2 - 59) and compared to 60-day reference values using linear mixed-effect regression models. Sensitivity analyses were conducted using 30- and 45-day references.

RESULTS

Across all participants, reliable estimates required a minimum of 8 days for TST and 6 days for SE and WASO. Participants with MCI required more days than controls (9 vs. 2 days for TST, 7 vs. 4 days for SE, and 6 vs. 2 days for WASO). Sensitivity analyses showed that shorter monitoring periods (30 and 45 days) could still provide reliable metrics.

CONCLUSIONS

To obtain reliable sleep metrics, at least 9 days of actigraphy data are needed for older adults with MCI, compared to 4 days for controls, suggesting the need for extended monitoring in cognitively impaired individuals.