In Surah An-Naba (78:9), the Quran declares: "And We made your sleep [a means for] rest" (وَجَعَلْنَا نَوْمَكُمْ سُبَاتًا). The Arabic term subat (سُبَاتًا) derives from the root sabata (سَبَتَ) which means "to cease," "to stop" or "to be at rest." This term evokes an interruption of activity, a temporary cessation of active functions.
This description of sleep as a "cessation" or "interruption of activity" is remarkably precise from a scientific point of view. Sleep is not a simple passive state, but a voluntary and regulated interruption of conscious activity, essential for survival.
The historical context
In the 7th century, the nature of sleep was completely unknown. Ancient civilizations considered it a mysterious state, sometimes associated with death or journeys of the soul. No scientific theory could explain why human beings sleep about a third of their lives.
It was only in the 20th century that science began to unravel the mysteries of sleep. In 1929, the invention of the electroencephalogram (EEG) by Hans Berger made it possible to record the electrical activity of the brain during sleep, opening the way to a scientific understanding of this phenomenon.
The discovery of REM sleep
In 1953, Eugene Aserinsky and Nathaniel Kleitman, researchers at the University of Chicago, discovered REM (Rapid Eye Movement) sleep, a phase of sleep characterized by rapid eye movements and intense brain activity [1]. This discovery revolutionized sleep research and led to the recognition and treatment of 84 distinct sleep and sleep-wake cycle disorders [5].
Sleep consists of several cycles, each lasting about 90 minutes, alternating between:
- Light NREM sleep (stages 1 and 2): transition phase and light sleep.
- Deep NREM sleep (stages 3 and 4): phase of physical recovery, growth hormone secretion and immune system strengthening.
- REM sleep: phase associated with dreams, memory consolidation and emotional regulation.
Deep sleep is particularly important for physical recovery: it is during this phase that the body repairs itself, tissues regenerate and growth hormone is secreted. The Quranic term subat, evoking a cessation of activity, corresponds well to this phase of deep rest where bodily activity is minimal.
Sleep and the brain
Modern research has shown that sleep is essential for brain function:
- Memory consolidation: During sleep, the brain transfers information from short-term to long-term memory.
- Toxin elimination: In 2013, researchers at the University of Rochester discovered that the brain's glymphatic system activates during sleep to eliminate metabolic waste, including beta-amyloid proteins associated with Alzheimer's disease.
- Emotional regulation: REM sleep plays a crucial role in processing emotions and regulating mood.
- Cellular repair: During deep sleep, the body secretes growth hormones and repairs damaged tissues.
The circadian rhythm
The Quran also mentions the alternation of day and night as a divine sign: "And it is He who made the night a clothing for you and sleep a rest and made the day a resurrection" (25:47). This alternation corresponds to the circadian rhythm, the internal biological clock of about 24 hours that regulates the sleep-wake cycle.
In 2017, Jeffrey C. Hall, Michael Rosbash and Michael W. Young received the Nobel Prize in Physiology or Medicine for their discoveries on the molecular mechanisms controlling the circadian rhythm. They identified the genes and proteins that regulate the internal biological clock, confirming that the day-night alternation is deeply inscribed in human biology.
Sleep in the Quran and Sunnah
The Quran mentions sleep several times as a sign of divine mercy: "And of His signs is your sleep by night and day and your seeking of His bounty" (30:23). Prophet Muhammad ﷺ also recommended healthy sleep practices, including going to bed early and waking up early, and taught supplications before sleeping.
Modern science confirms the importance of regular and sufficient sleep for physical and mental health. Sleep disorders are associated with an increased risk of cardiovascular disease, diabetes, obesity, depression and cognitive decline.