A review of sleep-related indicators measured in large population-based cohort studies in Japan.

BACKGROUND

How to measure sleep has been the primary focus of sleep epidemiological studies. To address the lack of systematic evaluation of sleep-related indicators, we reviewed large population-based cohort studies in Japan, focusing on whether sleep was measured subjectively or objectively.

METHODS

PubMed, Ichushi-Web, and official cohort study websites were systematically searched from January 1, 2004, to March 31, 2025, to identify studies that measured sleep-related indicators as exposures or outcomes in 19 large population-based cohorts in Japan. Data on sleep measurement methods and main study results were extracted.

RESULTS

Of 102 studies in 12 cohorts, 75 (74%) studies examined subjective sleep quantity or quality based on questionnaires, and 27 (26%) used objective measures of sleep. Among subjective measures, sleep duration was frequently self-reported (57 studies in 10 cohorts), while sleep quality was directly (e.g., "Do you think you get enough sleep?") or indirectly asked as part of sleep-related scores such as the Pittsburgh Sleep Quality Index (51 studies in 10 cohorts). Regarding objective measures, the Circulatory Risk in Communities Study cohort measured 3% oxygen desaturation index by pulse oximetry (9 studies) and respiratory disturbance index by airflow monitor (1 study), Japan Multi-Institutional Collaborative Cohort Study used actigraphy (1 study), Nagahama cohort used pulse oximetry (12 studies) and actigraphy (13 studies), and Tohoku Medical Megabank Project used actigraphy (1 study) and contactless biomotion sleep sensor (2 studies).

CONCLUSIONS

Population-based cohort studies in Japan have predominantly relied on subjective measures of sleep, while the number of studies using objective measures has been increasing.