large meal just before bedtime, requiring effort to metabolize it all, and hunger have been associated with disrupted sleep; clinicians may recommend eating a light snack before bedtime. Limiting intake of liquids before bedtime can prevent interruptions of sleep due to urination. Sleep environment Arranging a sleep environment that is quiet, very dark, and cool is recommended. Noises, light, and uncomfortable temperatures have been shown to disrupt continuous sleep. Other recommendations that are frequently made, though less studied, include selecting comfortable mattresses, bedding, and pillows, and eliminating a visible bedroom clock, to prevent focusing on time passing when trying to fall asleep. Light exposure when sleeping has been shown to cause ocular fatigue. In 2015, a systematic review of studies on mattresses concluded that medium-firm, custom-inflated mattresses were best for pain and neutral spinal alignment. Effectiveness Sleep hygiene studies use different sets of sleep hygiene recommendations, and the evidence that improving sleep hygiene improves sleep quality is weak and inconclusive . Most research on sleep hygiene principles has been conducted in clinical settings, and there is a need for more research on non-clinical populations. The strength of research support for each recommendation varies; some of the more robustly researched and supported recommendations include the negative effects of noisy sleep environments, alcohol consumption in the hours before sleep, engaging in mentally difficult tasks before sleep, and trying too hard to fall asleep. There is a lack of evidence for the effects of certain sleep hygiene recommendations, including getting a more comfortable mattress, removing bedroom clocks, not worrying, and limiting liquids. Other recommendations, such as the effects of napping or exercise, have a more complicated evidence base. The effects of napping, for example, seem to depend on the length and timing of napping, in conjunction with how much cumulative sleep an individual has had in recent nights. There is support showing positive sleep outcomes for people who follow more than one sleep hygiene recommendation. There is however no evidence that poor sleep hygiene can contribute to insomnia. While there is inconclusive evidence that sleep hygiene alone is effective as a treatment for insomnia, some research studies have shown improvement in insomnia for patients who receive sleep hygiene education in combination with cognitive behavioral therapy practices. The American Academy of Sleep Medicine released in 2021 a meta-analysis on behavioral therapies concluding that they "did not favor the use of sleep hygiene as a