Plain-language definitions grounded in the clinical and regulatory literature.
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
Sleep Measurement
What it isThe actual amount of time spent asleep during a sleep period, excluding time awake in bed. Measured by polysomnography or estimated by sleep diaries and wearables.
Why it mattersTST is the bottom-line number for whether you got enough sleep. Adults need 7-9 hours; chronic TST below 6 hours is associated with cardiovascular, metabolic, and cognitive consequences.
Think of it like thisIf sleep opportunity is the size of the glass, total sleep time is what’s actually in it. The NSF and AASM both publish age-specific recommendations for what that quantity should be.
The sum of all sleep stages (N1, N2, N3, REM) during a sleep period, derived from polysomnography by subtracting wake time after sleep onset and sleep onset latency from total recording time, typically expressed in minutes or hours.
MechanismTST reflects the interaction of sleep opportunity, sleep onset latency, sleep efficiency, and any awakenings during the sleep period. Adult TST varies inversely with age. TST is the strongest single predictor of next-day cognitive function and the dose-response variable for chronic sleep restriction effects on health.
Scientific ConsensusAdults require 7-9 hours of sleep nightly per AASM and NSF consensus. Chronic TST below 6 hours is associated with increased cardiovascular, metabolic, and all-cause mortality. Both insufficient and excessive TST show associations with mortality.
Active DebateWhether the J-shaped mortality curve reflects causal effects of long sleep or reverse causation. Individual variation in sleep need beyond population recommendations. The trade-off between TST and sleep continuity for next-day function.
Emerging ResearchGenetic determinants of natural short sleep (DEC2, ADRB1, NPSR1 variants in true short sleepers without consequences). Personalized sleep need recommendations based on genetic and phenotypic profiles. Wearable-based long-term TST tracking enabling population-level sleep epidemiology.
Key ResearchHirshkowitz et al. (2015) provided the National Sleep Foundation age-specific TST recommendations. Watson et al. (2015) provided the AASM joint consensus statement. Cappuccio et al. (2010) established the J-shaped mortality curve in meta-analysis.
— AASM/SRS canonical recommendation for adult TST
— Meta-analysis of TST-mortality J-shaped relationship
Sleep disorders, PTSD, and the invisible wounds of service can feel isolating. If you or someone you know is in crisis or experiencing thoughts of self-harm, help is available right now. The Veterans Crisis Line provides free, confidential support 24 hours a day, 7 days a week to veterans, service members, and their families.
If you are in crisis or experiencing thoughts of self-harm, call the Veterans Crisis Line at