Svefnþörf

Svefnþörf is an Icelandic term for sleep need, the amount of sleep a person requires to feel rested and function well during waking hours. It is not a fixed quantity shared by all individuals; it varies with age, genetics, health, and daily demands.

The regulation of svefnþörf is commonly described by the two-process model of sleep: Process S (homeostatic sleep pressure) and Process C (circadian rhythm). As wakefulness extends, sleep pressure builds, creating a drive to sleep. The circadian system modulates alertness and the timing of sleep across the 24-hour cycle. Sleep duration tends to align with an individual's sleep need, but insufficient or irregular sleep can generate a sleep debt that must be repaid.

Typical ranges and variability: Most adults function best on about 7–9 hours of sleep per night, though individual needs can vary by a couple of hours in either direction. Children and adolescents generally require more sleep, while older adults may need slightly less. Factors such as health, medications, stress, and physical activity can shift personal requirements, making svefnþörf a flexible parameter rather than a universal standard.

Measurement and implications: Sleep need can be inferred from patterns of daytime functioning, subjective sleepiness, and how readily one feels alert after a night's sleep. Chronic mismatch between desired and actual sleep, or consistently short sleep, is linked to impaired cognition, mood disturbances, and higher risk of various health problems, including metabolic and cardiovascular issues.

In summary, svefnþörf encompasses the individualized amount of sleep necessary for optimal functioning, shaped by biological regulation and modulated by life circumstances.