Sleep by Age Calculator Guide: How Much Sleep You Need at Every Age
Sleep needs are not one-size-fits-all. A newborn sleeps nearly 17 hours a day while a healthy adult functions best on 7 to 9. A teenager's biology pushes their bedtime later than a school-age child's, and a 70-year-old's sleep architecture looks nothing like a 30-year-old's. This guide walks through every age group — from birth to 65+ — with the latest recommendations from the National Sleep Foundation, the American Academy of Sleep Medicine, and the CDC. Use our sleep by age calculator to get personalized bedtime recommendations for your age.
Sleep by Age Calculator
Get personalized sleep recommendations based on National Sleep Foundation guidelines.
Adults need 7-9 hours per night. Most adults function best with 8 hours.
- Newborns (0–3 months) need 14–17 hours of sleep spread across the entire 24-hour day in irregular cycles
- Teenagers (14–17 years) need 8–10 hours but face a biological circadian delay that makes early school start times problematic
- Adults (18–64 years) need 7–9 hours — fewer than 3% of adults can function on less than 7 hours due to genetics
- Older adults (65+) need 7–8 hours but experience more fragmented sleep and less deep sleep as a normal part of aging
- Individual variation exists within every age group — genetics, activity level, health conditions, and sleep quality all modify how much sleep you personally need
- Complete Sleep Recommendations Table
- Sleep Needs by Age Chart
- Newborn Sleep (0–3 Months)
- Infant Sleep (4–11 Months)
- Toddler Sleep (1–2 Years)
- Preschool Sleep (3–5 Years)
- School-Age Sleep (6–13 Years)
- Teen Sleep (14–17 Years)
- Adult Sleep (18–64 Years)
- Senior Sleep (65+ Years)
- Sleep Architecture by Age
- Signs Your Child Isn't Getting Enough Sleep
- Sleep Tips for Every Age Group
- Frequently Asked Questions
Complete Sleep Recommendations Table
The table below reflects the 2015 National Sleep Foundation consensus guidelines, developed by a panel of 18 sleep scientists and medical experts. These remain the most widely referenced sleep duration recommendations and are endorsed by the AASM and the WHO. Use our sleep by age calculator to convert these into specific bedtimes for your schedule.
| Age Group | Age Range | Recommended | May Be Appropriate | Not Recommended |
|---|---|---|---|---|
| Newborn | 0–3 months | 14–17 hours | 11–13 or 18–19 hours | <11 or >19 hours |
| Infant | 4–11 months | 12–15 hours | 10–11 or 16–18 hours | <10 or >18 hours |
| Toddler | 1–2 years | 11–14 hours | 9–10 or 15–16 hours | <9 or >16 hours |
| Preschool | 3–5 years | 10–13 hours | 8–9 or 14 hours | <8 or >14 hours |
| School Age | 6–13 years | 9–11 hours | 7–8 or 12 hours | <7 or >12 hours |
| Teenager | 14–17 years | 8–10 hours | 7 or 11 hours | <7 or >11 hours |
| Young Adult / Adult | 18–64 years | 7–9 hours | 6 or 10 hours | <6 or >10 hours |
| Older Adult | 65+ years | 7–8 hours | 5–6 or 9 hours | <5 or >9 hours |
Sleep Needs by Age: Visual Chart
This visual representation shows how sleep requirements decrease from infancy through adulthood. According to NIH research, understanding these patterns helps families establish appropriate sleep schedules. Our sleep cycle calculator can help you time sleep periods optimally.
Newborn Sleep (0–3 Months)
Newborns sleep 14 to 17 hours per day, but this sleep is fundamentally different from older children and adults. A newborn's circadian rhythm has not yet developed — their suprachiasmatic nucleus (SCN) begins receiving light cues at birth but takes approximately 3 months to establish a functional day-night pattern. As a result, newborn sleep is polyphasic: distributed in 2- to 4-hour bursts around the clock, with no distinction between day and night.
Newborn sleep cycles are also much shorter than adult cycles — about 50 minutes compared to the adult's 90 minutes. Roughly half of newborn sleep is spent in active sleep (the newborn equivalent of REM), which is critical for the rapid brain development occurring during this period. This explains why newborns twitch, smile, and make faces during sleep. Learn more about sleep stages in our detailed guide.
Newborn Sleep Distribution (24 Hours)
Safe Sleep Practices and SIDS Prevention
The American Academy of Pediatrics (AAP) recommends the following safe sleep guidelines to reduce the risk of Sudden Infant Death Syndrome (SIDS). The Johns Hopkins Medicine emphasizes these practices as the most effective SIDS prevention:
- Back to sleep: Always place infants on their backs for every sleep, both naps and nighttime
- Firm, flat surface: Use a firm mattress in a safety-approved crib with a fitted sheet — no soft bedding, pillows, bumper pads, or stuffed animals
- Room sharing without bed sharing: The AAP recommends the infant sleep in the parents' room (but on a separate surface) for at least the first 6 months
- Avoid overheating: Dress the infant in no more than one additional layer than an adult would wear
- Offer a pacifier: Pacifier use at nap time and bedtime has been associated with a reduced risk of SIDS
Infant Sleep (4–11 Months)
Between 4 and 11 months, total sleep needs decrease slightly to 12 to 15 hours per day. More importantly, this is the period when sleep begins to consolidate. By 4 months, the circadian rhythm is functional, and most infants start developing a recognizable day-night pattern. By 6 months, many (though not all) infants are capable of sleeping a 6- to 8-hour stretch at night. Use our bedtime calculator to find optimal sleep times.
Sleep Regressions
Sleep regressions are temporary disruptions in an infant's sleep pattern, typically lasting 2 to 6 weeks. They often coincide with developmental milestones. The most common regression occurs around 4 months, when the infant's sleep architecture matures from the two-stage newborn pattern to the four-stage adult-like pattern. Other common regression windows are 8 months (separation anxiety, crawling) and 12 months (walking, language). The Cleveland Clinic provides detailed guidance on managing these periods.
Common Sleep Regression Ages
Typical Infant Sleep Schedule
| Age | Nighttime Sleep | Naps | Total Sleep |
|---|---|---|---|
| 4 months | 10–11 hours (with 1–2 wakings) | 3 naps (3–4 hrs total) | 14–15 hours |
| 6 months | 10–11 hours (0–1 waking) | 2–3 naps (2.5–3.5 hrs) | 13–14 hours |
| 9 months | 10–12 hours | 2 naps (2–3 hrs total) | 12–14 hours |
| 11 months | 10–12 hours | 2 naps (2–2.5 hrs total) | 12–14 hours |
Night waking is developmentally normal during this period. Studies published in the National Library of Medicine show that approximately 30–40% of infants still wake at least once per night at 12 months. This does not indicate a sleep problem — it is within the range of normal infant development.
Toddler Sleep (1–2 Years)
Toddlers need 11 to 14 hours of total sleep, typically split between nighttime sleep (10–12 hours) and one or two daytime naps. The biggest sleep transition during this period is the two-to-one nap transition, which usually occurs between 12 and 18 months. Most toddlers drop their morning nap first, consolidating daytime sleep into a single afternoon nap of 1.5 to 3 hours. WebMD offers additional guidance on toddler nap transitions.
Signs Ready for 1 Nap
Consistently fighting morning nap, taking 30+ minutes to fall asleep, afternoon nap pushes bedtime late, age 15-18 months
Signs Need 2 Naps Still
Overtired by afternoon, meltdowns before dinner, falling asleep in car, age under 14 months typically
Bedtime Resistance and Nighttime Fears
Bedtime resistance peaks during the toddler years. Common causes include separation anxiety (which surges around 18 months), the desire for autonomy ("No!"), overtiredness, and inconsistent routines. Nighttime fears also begin to emerge around age 2 as imagination develops. Strategies include:
- A consistent, predictable 20–30 minute bedtime routine (bath, book, song, lights out)
- Offering limited choices ("Do you want the blue pajamas or the green pajamas?")
- Using a dim nightlight for children who express fear of the dark
- Setting firm, calm boundaries and avoiding prolonged negotiations
Typical Toddler Sleep Schedule
| Age | Wake Time | Nap | Bedtime | Total Sleep |
|---|---|---|---|---|
| 12–15 months | 6:00–7:00 AM | 2 naps (2.5–3 hrs total) | 7:00–8:00 PM | 12–14 hours |
| 15–18 months | 6:00–7:00 AM | Transitioning to 1 nap (2–3 hrs) | 7:00–7:30 PM | 12–13 hours |
| 18–24 months | 6:30–7:30 AM | 1 nap (1.5–2.5 hrs) | 7:00–8:00 PM | 11–14 hours |
Preschool Sleep (3–5 Years)
Preschoolers need 10 to 13 hours of total sleep. The major sleep milestone during this period is nap elimination. Most children drop their afternoon nap between ages 3 and 5, with the average falling around 3.5 years. Signs that a child is ready to drop the nap include consistently resisting the nap, taking more than 30 minutes to fall asleep at nap time, or the nap causing bedtime to push later and later. The Journal of Pediatrics documents these developmental transitions.
When Children Stop Napping
The transition should be gradual. Replace the nap with a "quiet time" period (30–60 minutes of books, puzzles, or calm play) and temporarily move bedtime 30–45 minutes earlier to compensate for the lost daytime sleep. Most children adjust within 2–4 weeks.
Nightmares vs. Night Terrors
Both nightmares and night terrors are common in preschoolers, but they are fundamentally different events. Understanding the distinction helps parents respond appropriately. For more on sleep stages and when these occur, see our sleep stages guide.
| Feature | Nightmare | Night Terror |
|---|---|---|
| Sleep stage | REM sleep (second half of night) | Deep NREM sleep (first third of night) |
| Timing | Typically after midnight | Usually 1–3 hours after falling asleep |
| Child's state | Wakes up, is aware, seeks comfort | Appears awake but is not; may scream, thrash, sweat |
| Memory | Remembers the dream | No memory of the event |
| Duration | Child wakes, then needs help falling back asleep | 1–15 minutes, then returns to sleep spontaneously |
| Response | Comfort the child; reassure them they are safe | Do not try to wake the child; ensure physical safety |
| Peak age | 3–6 years (but occurs at all ages) | 3–7 years |
| Prevalence | Nearly universal in children | ~3–6% of children |
Night terrors are more alarming for parents than for the child. They are associated with overtiredness, fever, and sleep deprivation. Ensuring adequate total sleep is the most effective prevention. If night terrors occur frequently and at a predictable time, scheduled awakenings (gently rousing the child 15 minutes before the typical episode) can break the cycle. Consult a pediatrician if episodes are frequent or violent.
School-Age Sleep (6–13 Years)
School-age children need 9 to 11 hours of sleep per night. By this age, naps have typically been eliminated, and all sleep occurs in a single consolidated nighttime block. This is the age group where the connection between sleep and academic performance becomes most evident. Our wake-up calculator can help parents determine the optimal bedtime based on school start times.
Impact of Sleep Deprivation on School Performance
Sleep and Academic Performance
Research consistently demonstrates a strong link between sleep duration and cognitive function in children. A study published in the journal Pediatrics found that each additional hour of sleep was associated with measurable improvements in attention, working memory, and academic grades. Sleep-deprived children show reduced prefrontal cortex activity — the brain region responsible for planning, impulse control, and complex reasoning. The Harvard Health team has documented these effects extensively.
Screen Time Impact
Screen time is the number one sleep disruptor for school-age children. The American Academy of Pediatrics reports that children with a television or device in their bedroom sleep an average of 20–30 minutes less per night than those without. The mechanisms are threefold: blue light suppresses melatonin, stimulating content increases arousal, and device use displaces sleep time. Establish a firm rule: all screens off at least 1 hour before bedtime, and no screens in the bedroom overnight.
Teen Sleep (14–17 Years)
Teenagers need 8 to 10 hours of sleep, but the reality is grim: the CDC reports that over 70% of high school students get fewer than 8 hours on school nights. This is not simply a discipline problem — it is a collision between biology and society.
The Circadian Shift
During puberty, the circadian clock undergoes a biological delay of 1 to 3 hours. Melatonin onset shifts later, making it physiologically difficult for most teenagers to fall asleep before 11:00 PM. Simultaneously, early school start times (often 7:00–7:30 AM) force teens to wake during what their body considers the middle of the night. The result is chronic sleep deprivation during one of the most critical developmental periods of life.
Adult Melatonin Release
Begins around 9:00 PM, peaks at midnight, enables falling asleep by 10:00-10:30 PM naturally
Teen Melatonin Release
Delayed 1-3 hours, begins 10:00 PM-midnight, makes falling asleep before 11:00 PM biologically difficult
The American Academy of Sleep Medicine and the American Academy of Pediatrics have recommended that middle and high schools start no earlier than 8:30 AM to align with adolescent circadian biology. States including California and Florida have passed legislation mandating later start times, with early data showing improvements in attendance, grades, and mental health. Sleep Foundation research documents these policy changes.
Social Media and Teen Sleep
Social media compounds the biological challenge. A 2023 meta-analysis published in PubMed Central found that adolescents who use social media for more than 3 hours per day are twice as likely to report poor sleep quality and delayed sleep onset. The combination of blue light, social stimulation, fear of missing out, and the dopamine feedback loops of notifications creates a powerful barrier to timely sleep onset. Learn more in our circadian rhythm guide.
Social Media Use vs Sleep Quality in Teens
Adult Sleep (18–64 Years)
The adult recommendation of 7 to 9 hours per night is the most widely cited sleep guideline, and it is backed by extensive epidemiological data. The AASM specifically recommends a minimum of 7 hours, based on a systematic review of over 5,000 studies examining the relationship between sleep duration and health outcomes.
Within the 7–9 hour range, individual need varies based on several factors:
- Genetics: The DEC2 gene mutation allows a small fraction (less than 3%) to function on 6 hours. Everyone else who claims to "do fine" on 6 hours is experiencing accumulated sleep debt they have normalized.
- Physical activity: Athletes and people with physically demanding jobs typically need 8–9 hours for adequate recovery. See our optimal sleep duration guide.
- Health conditions: Illness, recovery from surgery, chronic pain, and mental health conditions like depression often increase sleep need temporarily or permanently.
- Sleep quality: If your sleep is frequently interrupted (by a partner, children, noise, or a sleep disorder), you may need more total time in bed to accumulate enough restorative sleep.
- Pregnancy: Sleep need increases during pregnancy, particularly in the first and third trimesters. According to Mayo Clinic, pregnant women should aim for at least 8–9 hours.
Health Risks of Sleeping Less Than 7 Hours
Senior Sleep (65+ Years)
Older adults are recommended 7 to 8 hours, but the structure of their sleep changes significantly. These changes are a normal part of aging, not a sign of disease, though they can be exacerbated by medical conditions and medications. The National Institute on Aging provides comprehensive resources for understanding sleep in older adults.
How Sleep Architecture Changes with Age
- Less deep sleep: Time spent in Stage 3 (deep/slow-wave sleep) declines steadily after age 30. By age 70, deep sleep may represent only 5–10% of total sleep time, compared to 15–20% in young adults.
- More fragmented sleep: Older adults wake more frequently during the night and spend more time in lighter sleep stages. This often leads to the perception of "not sleeping well" even when total sleep time is adequate.
- Advanced circadian phase: The circadian clock shifts earlier with age. Many older adults feel sleepy by 8–9 PM and wake naturally by 4–5 AM. This is biologically normal, not a disorder.
- Increased daytime napping: The combination of fragmented nighttime sleep and reduced circadian amplitude leads many older adults to nap during the day. Short naps (20–30 minutes) are fine; long naps may further disrupt nighttime sleep.
Sleep Stage Distribution: Young Adult vs Senior
Medication Effects on Sleep
Many medications commonly prescribed to older adults affect sleep. Beta-blockers can suppress melatonin. Diuretics cause nighttime urination. Corticosteroids increase arousal. Some antidepressants suppress REM sleep, while others cause sedation. If you are experiencing sleep problems and take multiple medications, discuss potential sleep effects with your physician. The Mayo Clinic provides guidance on managing sleep in older adults.
Common Sleep Issues in Adults 65+
| Condition | Prevalence | Key Symptoms | Treatment |
|---|---|---|---|
| Sleep Apnea | 20-30% | Snoring, gasping, daytime sleepiness | CPAP, weight loss, positional therapy |
| Insomnia | 40-50% | Difficulty falling/staying asleep | CBT-I, sleep hygiene, medication review |
| Restless Legs | 10-35% | Urge to move legs, worse at night | Iron supplements, dopamine agonists |
| REM Behavior Disorder | 1-2% | Acting out dreams, kicking | Melatonin, clonazepam, safety measures |
Sleep disorders also become more prevalent with age. Sleep apnea affects an estimated 20–30% of adults over 65, and insomnia symptoms are reported by nearly half. The Sleep Foundation and Cleveland Clinic offer detailed information on diagnosis and treatment. See our sleep disorders guide for comprehensive information.
Sleep Architecture by Age
Sleep is not a uniform state — it consists of distinct stages that cycle throughout the night. According to NIH research, the proportion of time spent in each stage changes dramatically across the lifespan. Understanding these changes helps explain why sleep quality feels different at various ages.
Sleep Stage Distribution Across the Lifespan
Why Sleep Stages Matter at Different Ages
| Sleep Stage | Primary Function | Most Critical Age | Health Impact |
|---|---|---|---|
| REM Sleep | Brain development, memory consolidation, emotional processing | Infants and children | Learning, creativity, mood regulation |
| Deep Sleep (N3) | Physical restoration, growth hormone release, immune function | Children and teens | Growth, tissue repair, metabolism |
| Light Sleep (N1-N2) | Transition, memory encoding, body maintenance | All ages | Cardiovascular health, motor learning |
Signs Your Child Isn't Getting Enough Sleep
Sleep deprivation in children often looks different from adult tiredness. While adults become visibly drowsy, sleep-deprived children frequently become hyperactive, irritable, and emotionally dysregulated — symptoms that can mimic ADHD. Here are the warning signs by age group, as documented by the Mayo Clinic:
- Excessive fussiness or inconsolable crying, especially in the late afternoon
- Difficulty settling for sleep despite being tired (overtired)
- Shorter-than-expected naps (consistently under 30 minutes)
- Waking excessively at night beyond what is developmentally expected
- Rubbing eyes, pulling ears, or yawning frequently during the day
- Difficulty waking in the morning; needs multiple alarms or parent interventions
- Hyperactivity, impulsivity, or difficulty concentrating (can mimic ADHD)
- Emotional outbursts or meltdowns that seem disproportionate to the trigger
- Falling asleep in the car on short rides or during quiet activities
- Declining grades or teacher reports of inattention
- Frequent illness due to immune suppression from inadequate sleep
- Sleeping until noon or later on weekends (a sign of chronic weekday sleep debt)
- Irritability, mood swings, or symptoms of anxiety and depression
- Reliance on caffeine or energy drinks to get through the day
- Falling asleep in class or during homework
- Difficulty with memory, decision-making, or emotional regulation
- Increased risk-taking behavior and impaired driving reaction times
Sleep Tips for Every Age Group
Newborns
Follow safe sleep guidelines from the AAP. Expose baby to natural daylight during awake periods to help develop circadian rhythm. Keep nighttime feedings dim and quiet. Swaddling can help newborns feel secure (stop when baby shows signs of rolling).
Infants
Establish a simple, consistent bedtime routine. Put baby down drowsy but awake to develop self-soothing skills. Maintain a dark, cool sleep environment. Expect regressions around 4, 8, and 12 months — they are temporary.
Toddlers
Keep a predictable 20–30 minute bedtime routine. Offer limited choices to satisfy the need for autonomy. Use a dim nightlight if fears emerge. Transition from crib to bed only when necessary (typically after age 2). Maintain consistent nap timing.
Preschoolers
Transition from nap to quiet time when ready. Move bedtime earlier when the nap is dropped. Use positive reinforcement for staying in bed. Address nighttime fears with comfort objects and reassurance, not logic. Avoid scary content in media.
School-Age
No screens in the bedroom. Set a firm screen curfew 1 hour before bed. Maintain the same bedtime on school nights and weekends (within 30–60 min). Encourage physical activity during the day. Our sleep hygiene guide has a full bedtime routine checklist.
Teenagers
Prioritize consistent wake times, even on weekends. Limit caffeine after noon. Charge phones outside the bedroom. Get morning sunlight to anchor the circadian rhythm. Avoid all-nighters — the academic benefit of extra study is outweighed by cognitive impairment from sleep loss.
Adults
Aim for 7–9 hours consistently. Use our bedtime calculator to align with sleep cycle boundaries. Follow the 10-3-2-1-0 rule: no caffeine 10 hrs before bed, no food 3 hrs, no work 2 hrs, no screens 1 hr, 0 snooze hits. See our sleep hygiene tips.
Seniors
Maintain regular sleep-wake times. Limit naps to 20–30 min before 3 PM. Get bright light exposure in the morning. Review medications for sleep side effects with your doctor. Stay physically active. Consider a sleep evaluation if snoring or daytime sleepiness is significant.
Universal Sleep Optimization Tips
Consistent Schedule
Go to bed and wake up at the same time every day, including weekends. This reinforces your body's circadian rhythm and improves sleep quality over time.
Optimal Environment
Keep your bedroom cool (65-68F/18-20C), dark, and quiet. Consider blackout curtains and white noise if needed. Remove all electronic devices from the sleeping area.
Wind-Down Routine
Establish a 30-60 minute relaxation period before bed. This signals to your brain that sleep is approaching. Include activities like reading, gentle stretching, or meditation.
Morning Light Exposure
Get 15-30 minutes of bright light within an hour of waking. This helps set your circadian clock and improves nighttime sleep quality.
Foods and Substances That Affect Sleep
Sleep Disruptors
Caffeine (half-life 5-6 hours), alcohol (fragments sleep), heavy meals within 3 hours of bed, excessive fluids before sleep, nicotine (stimulant effect).
Sleep Promoters
Tart cherry juice (natural melatonin), magnesium-rich foods, light protein snack if hungry, herbal teas (chamomile, valerian), warm milk.
Sleep Habits Comparison
Optimal Sleep Habits
Consistent bedtime, dark cool room, no screens 1hr before bed, regular exercise, morning light exposure, relaxation routine
Poor Sleep Habits
Variable schedule, screen use in bed, caffeine after noon, irregular exercise, bright evening lights, racing thoughts at bedtime
When to Use Calculators
Use our bedtime calculator to plan when to sleep, wake-up calculator for morning planning, sleep debt calculator to track deficits
When to See a Doctor
Chronic insomnia lasting 3+ months, loud snoring or gasping, extreme daytime sleepiness, acting out dreams, restless leg symptoms
Frequently Asked Questions
Newborns (0–3 months) need 14 to 17 hours of sleep per 24-hour period. This sleep is polyphasic, occurring in short bursts of 2 to 4 hours around the clock because their circadian rhythm has not yet developed. By 3 months, most infants begin consolidating longer stretches at night. Follow the AAP safe sleep guidelines for all infant sleep.
Teenagers (14–17) need 8 to 10 hours because their brains are undergoing critical development, including synaptic pruning and myelination. Puberty also causes a biological shift in circadian rhythm, delaying melatonin release by 1 to 3 hours. This makes it biologically difficult for most teens to fall asleep before 11 PM. The AASM recommends school start times no earlier than 8:30 AM to accommodate this shift.
The recommended range for adults 65+ is 7 to 8 hours, only slightly less than younger adults. However, sleep architecture changes significantly: less deep sleep, more awakenings, and an earlier circadian phase. These changes are normal, but frequent awakenings may also be caused by medications, pain, or sleep disorders like sleep apnea, which affects 20–30% of older adults.
A 10-year-old needs 9 to 11 hours. For a 6:30 AM school wake time, bedtime should be between 7:30 PM and 9:30 PM. Aiming for the earlier end ensures closer to 11 hours. Keep the same bedtime on weekends (within 30–60 minutes) to maintain a stable circadian rhythm. Use our sleep by age calculator for a personalized recommendation.
Yes, bedtime resistance is extremely common between ages 1 and 3. It typically stems from separation anxiety, desire for autonomy, or inconsistent routines. A predictable 20–30 minute bedtime routine, limited choices, and firm but calm boundaries are the most effective strategies. Most toddlers outgrow significant bedtime resistance by age 4.
Most children drop their afternoon nap between ages 3 and 5, with the average around 3.5 years. Signs of readiness include consistently resisting the nap, taking over 30 minutes to fall asleep at nap time, or the nap delaying bedtime. Replace the nap with quiet time and temporarily move bedtime earlier to compensate.
Screen time disrupts sleep through three mechanisms: blue light suppresses melatonin, stimulating content increases arousal, and device use displaces sleep time. The AAP reports children with bedroom screens sleep 20–30 minutes less per night. Remove all screens from the bedroom and enforce a 1-hour pre-bed screen curfew.
Less than 3% of adults carry the DEC2 gene mutation that allows genuine function on 6 hours. The vast majority of adults sleeping only 6 hours show measurable declines in cognitive performance, reaction time, and immune function — even if they feel subjectively adapted. Research from Harvard Medical School shows that chronic 6-hour sleep increases disease risk significantly. The minimum for most adults is 7 hours per the AASM.
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