title: The effect of intermittent fasting during Ramadan on sleep, sleepiness, cognitive function, and circadian rhythm.
abstract: OBJECTIVE
  Studies have shown that experimental fasting can affect cognitive function, sleep, and wakefulness patterns. However, the effects of experimental fasting cannot be generalized to fasting during Ramadan due to its unique characteristics. Therefore, there has been increased interest in studying the effects of fasting during Ramadan on sleep patterns, daytime sleepiness, cognitive function, sleep architecture, and circadian rhythm.
  
  
  METHODS
  In this review, we critically discuss the current research findings in those areas during the month of Ramadan.
  
  
  RESULTS
  Available data that controlled for sleep/wake schedule, sleep duration, light exposure, and energy expenditure do not support the notion that Ramadan intermittent fasting increases daytime sleepiness and alters cognitive function. Additionally, recent well-designed studies showed no effect of fasting on circadian rhythms. However, in non-constrained environments that do not control for lifestyle changes, studies have demonstrated sudden and significant delays in bedtime and wake time.
  
  
  CONCLUSIONS
  Studies that controlled for environmental factors and sleep/wake schedule reported no significant disturbances in sleep architecture. Nevertheless, several studies have consistently reported that the main change in sleep architecture during fasting is a reduction in the proportion of REM sleep.
authors.affiliation: University Sleep Disorders Center, College of Medicine, King Saud University, Box 225503, Riyadh, 11324, Saudi Arabia.|Strategic Technologies Program of the National Plan for Sciences and Technology and Innovation, Riyadh, Saudi Arabia.
authors.forename: Shaden O
authors.initials: SO
authors.lastname: Qasrawi
authors.affiliation: University Sleep Disorders Center, College of Medicine, King Saud University, Box 225503, Riyadh, 11324, Saudi Arabia.|Strategic Technologies Program of the National Plan for Sciences and Technology and Innovation, Riyadh, Saudi Arabia.
authors.forename: Seithikurippu R
authors.initials: SR
authors.lastname: Pandi-Perumal
authors.affiliation: University Sleep Disorders Center, College of Medicine, King Saud University, Box 225503, Riyadh, 11324, Saudi Arabia. ashammam2@gmail.com.|Strategic Technologies Program of the National Plan for Sciences and Technology and Innovation, Riyadh, Saudi Arabia. ashammam2@gmail.com.
authors.forename: Ahmed S
authors.initials: AS
authors.lastname: BaHammam
mesh_terms: D002940:Circadian Rhythm / Q000502:physiology*; D003071:Cognition / Q000502:physiology*; D005215:Fasting / Q000502:physiology*; D006693:Holidays; D006801:Humans; D007514:Islam; D012890:Sleep / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology*
keywords: Alertness; Caloric intake; Chronotype; Cognitive function; Food; Light; Sleep architecture