Total sleep time is the duration of time (hours, minutes, and/or seconds) spent sleeping in the primary sleep period. Total sleep time (TST) is a core measure because it is an important indicator of health and mortality. Adequate TST is crucial for maintaining physical and mental well-being, as insufficient sleep duration has been linked to increased all-cause mortality and increased risk for various health issues, such as obesity, cardiovascular disease, impaired immune function, and cognitive deficits.
TST is a key parameter in diagnosing sleep disorders such as insomnia, sleep apnea, and hypersomnia. Researchers use objective methods such as polysomnography (PSG) and actigraphy, along with subjective measures like sleep diaries, to assess TST. Understanding TST helps researchers and clinicians evaluate sleep quality and develop interventions to improve sleep health. Beyond primary sleep disorders, the relationship between TST and underlying medical conditions is two-sided: sleep can be affected by many conditions such as pain, shortness of breath, autonomic nervous system disorders, hormonal imbalance, autoimmune and metabolic disorders, and environmental factors such as work schedule or habitat, and inadequate sleep time can exacerbate existing medical conditions. As a general health indicator, measuring TST and comparing it with the healthy range can reveal a systematically accumulated sleep debt or oversleeping.