Chronotypes in the US - Influence of age and sex.
Level 4 - case-series / case-control
Cross-sectional analysis of pooled national survey diary data
PubMed 28636610 · doi:10.1371/journal.pone.0178782
What was done
Researchers evaluated 12 years (2003–2014) of pooled time-use diary data from the American Time Use Survey (ATUS) to estimate population-level chronotypes across age and sex in the United States. Chronotype was calculated from the mid-point of sleep on weekends (MSFWe) across 53,689 participants.
What was found
Chronotype followed a near-normal distribution overall and within age subgroups. The mean shifted later during adolescence, peaking in 'lateness' at approximately 19 years of age before shifting earlier across older age groups. Males showed later chronotypes than females prior to age 40, but earlier chronotypes after age 40. The largest age-related differences occurred between ages 15 and 25 for both sexes, accounting for over 50% of the total chronotype variance across all age groups. Chronotype variability declined with increasing age and was generally higher in males than females.
Why it matters
This provides large-scale normative data on sleep timing and circadian patterns across the human lifespan in the US. The finding that adolescents exhibit the latest chronotypes provides empirical support for delaying school start times and adopting flexible work schedules.
Limits
The abstract reports relative patterns rather than exact numerical mid-point sleep times, confidence intervals, or standard deviations. Chronotype was estimated from self-reported weekend sleep timing rather than objective circadian physiological markers (such as dim-light melatonin onset), and the cross-sectional design cannot directly track individual longitudinal trajectories.
Cited by
- supports The majority of the human population has an intermediate chronotype, naturally preferring to wake up between 6:00 a.m. and 8:00 a.m. and go to sleep between 10:00 p.m. and midnight.