The library
These are things people say about sleep—not recommendations. Each topic includes the research record and an explicit verdict.
20 of 20 reviewed topics
Substances
What people say
“I can drink caffeine in the afternoon and still sleep normally.”
What the evidence says
Grade A · StrongIn a small controlled study, caffeine taken six hours before bed reduced total sleep time and changed sleep measures, even when people did not fully notice the disruption.
Tech
What people say
“A phone or e-reader before bed has no real effect if I feel sleepy.”
What the evidence says
Grade B · ModerateA crossover laboratory study found that evening use of a light-emitting e-reader delayed circadian timing and reduced next-morning alertness compared with print reading.
Environment
What people say
“A television, lamp, or outdoor light in the room cannot affect my sleep.”
What the evidence says
Grade B · ModerateObservational research links light during sleep with health outcomes, but it cannot prove the light caused them. A darker room is a low-risk environmental experiment, not treatment.
Timing
What people say
“I can sleep very little on weekdays and make all of it up at the weekend.”
What the evidence says
Grade B · ModerateIn a laboratory protocol, weekend recovery sleep did not prevent several adverse metabolic effects after repeated sleep restriction. This does not establish an individual health diagnosis.
Substances
What people say
“Alcohol helps me sleep better because I fall asleep faster.”
What the evidence says
Grade B · ModerateAlcohol can shorten sleep-onset time for some people, but controlled research reports later-night sleep disruption and altered sleep stages. Falling asleep faster is not the same as better sleep.
Behaviour
What people say
“Any workout after dinner will ruin my sleep.”
What the evidence says
Grade B · ModerateA systematic review found evening exercise was not generally associated with worse sleep in healthy adults. Very intense exercise ending close to bedtime may be different for some people.
Environment
What people say
“The warmer my bedroom is, the more deeply I will sleep.”
What the evidence says
Grade C · LimitedThermoregulation is involved in sleep onset and maintenance, but the best room temperature varies by bedding, clothing, season, and person. There is no universal magic number.
Substances
What people say
“Melatonin will reliably knock me out whenever I cannot sleep.”
What the evidence says
Grade B · ModerateEvidence supports melatonin for some circadian-timing situations, including jet lag, but effects and appropriate use depend on timing and context. It is not a universal sleep solution.
Environment
What people say
“White noise is universally good for sleep.”
What the evidence says
Grade C · LimitedStudies of continuous noise are varied and often small. It may mask intermittent sound for some people, but the evidence does not establish a universal sleep benefit or a single safe setting.
Tech
What people say
“My phone can stay by the bed because I am not actively using it.”
What the evidence says
Grade C · LimitedCross-sectional studies associate nighttime phone use with poorer sleep, but they cannot separate the device from stress, habits, or existing sleep problems. Notifications are a practical variable to test locally.
Timing
What people say
“I should never nap if I want to sleep at night.”
What the evidence says
Grade C · LimitedNap effects depend on duration, timing, prior sleep, and the person. Research does not support treating every nap as harmful, though later or longer naps can reduce sleep pressure.
Timing
What people say
“As long as I get enough hours, my sleep timing can be completely different every day.”
What the evidence says
Grade B · ModerateLarge observational research links irregular sleep timing with adverse health outcomes. It cannot prove timing irregularity caused those outcomes, but it suggests regularity is more than an aesthetic goal.
Behaviour
What people say
“If I sleep badly once, I have permanently harmed my brain or body.”
What the evidence says
Grade D · EarlyShort-term sleep loss can affect alertness and performance, but claims of permanent damage from one ordinary bad night are not supported by the studies cited here. Persistent concerns deserve clinical discussion.
Tech
What people say
“My consumer wearable tells me exactly how much deep sleep I got.”
What the evidence says
Grade B · ModerateConsumer devices can be useful for patterns over time, but validation studies show imperfect agreement with polysomnography, especially for sleep stages. They are not diagnostic tests.
Tech
What people say
“Doomscrolling relaxes me enough to make sleep easier.”
What the evidence says
Grade C · LimitedDevice use is often associated with later bedtimes and poorer subjective sleep, but content, light, stress, and timing are intertwined. The evidence cannot say every scroll session causes poor sleep.
Behaviour
What people say
“Going to bed very full makes sleep deeper.”
What the evidence says
Grade C · LimitedMeal timing and sleep research is still limited and confounded by dietary patterns. There is not strong evidence that a heavy pre-bed meal improves sleep quality for most people.
Environment
What people say
“It does not matter when I get daylight; only bedtime matters.”
What the evidence says
Grade B · ModerateHuman circadian experiments show light can shift biological timing, with effects depending on when it is received. This supports light timing as one factor, not a stand-alone cure for insomnia.
Timing
What people say
“Multiple alarms and snoozes do not affect how I feel in the morning.”
What the evidence says
Grade D · EarlyThere is little direct experimental evidence about repeated snoozing. It can fragment the final part of sleep, but the size and importance of that effect varies and remains under-studied.
Behaviour
What people say
“Taping my mouth shut at night is a harmless way to improve sleep.”
What the evidence says
Grade D · EarlyThere is not enough high-quality evidence to support a universal benefit, and restricting the mouth during sleep may be unsafe for some people. This is not a general sleep recommendation.
Tech
What people say
“Tracking every sleep metric will make me sleep better.”
What the evidence says
Grade C · LimitedSleep tracking can help some people notice patterns, but clinical commentary describes orthosomnia: an unhelpful preoccupation with optimizing tracker data. Better data is not always better sleep.