How many hours of sleep you really need to stay healthy

Quick answer

Most healthy adults should aim for 7–9 hours of sleep nightly, with at least 7 hours considered the minimum to avoid many health risks. Sleeping consistently less than about 7 hours is linked to higher risks of metabolic, cardiovascular, and mental-health problems; sleeping substantially more than typical (often >9 hours) is also associated with some health risks and may signal an underlying condition.

Why sleep duration matters

Sleep is not optional — it’s a biological necessity. While people vary in their exact needs, scientific bodies and large reviews show a consistent pattern: both short and long sleep durations correlate with worse health outcomes, and regularity and quality of sleep matter too. Sleep influences immune function, glucose metabolism, appetite hormones, blood pressure, mental health, memory consolidation, and the body’s inflammatory response.

Recommended sleep by age (practical guide)

Newborns (0–3 months): 14–17 hours.
Infants (4–12 months): 12–16 hours (including naps).
Toddlers / preschoolers: 10–14 hours (varies by age).
School-age children (6–12): 9–12 hours.
Teenagers (13–17): 8–10 hours.
Adults (18–64): 7–9 hours recommended; at least 7 hours to avoid risks.
Older adults (65+): often 7–8 or 7–9 hours depending on guidelines and individual needs.

These ranges are consensus recommendations from major sleep organizations and public health agencies. Individual needs vary (some people function well on slightly less or slightly more), but population-level data show the above ranges are associated with best outcomes.

What happens when you sleep too little

Consistently getting less sleep than recommended (commonly defined as <7 hours for adults) is linked to:

Higher risk of cardiovascular disease and hypertension. Short sleep is associated with increased incidence of heart disease and high blood pressure.
Increased risk of diabetes and impaired glucose tolerance. Short sleep alters glucose metabolism and insulin sensitivity.
Weight gain and obesity. Short sleep affects hunger hormones (ghrelin, leptin) and appetite regulation, increasing risk of overeating and weight gain.
Poor mental health and cognitive effects. Insufficient sleep increases risk of anxiety, depression, reduced concentration, memory lapses, and slower reaction times (important for driving and workplace safety).
Higher mortality risk. Large population studies and meta-analyses show small but significant increases in overall mortality for short sleepers.

Mechanisms include chronic inflammation, dysregulated hormones, sympathetic nervous system activation (stress response), and impaired restorative brain processes that normally occur during sleep.

What about oversleeping — can you sleep too much?

Multiple studies find that long sleep durations (commonly >9 hours) are also associated with adverse outcomes:

Associations with higher mortality and cardiovascular risk. Population studies and meta-analyses report increased risk of death and cardiovascular disease among long sleepers, though causality is less clear than for short sleep. Long sleep may be both a risk marker and a consequence of underlying disease.
Higher rates of diabetes and stroke in some studies. Several reviews link long nightly sleep with higher incidence of diabetes and stroke, but interpretations vary: long sleep could reflect poor sleep quality, depression, low physical activity, or chronic illness.

Important nuance: unlike short sleep, excessive sleep is often a sign rather than a direct proven cause. People who regularly sleep >9 hours should consider medical evaluation to rule out sleep disorders (like sleep apnea), depression, inflammatory or neurological diseases, or medication side effects.

Sleep regularity and quality — as important as quantity

Recent research highlights that irregular sleep schedules (big differences in sleep/wake times) increase cardiovascular risk even when total hours appear adequate. Regular bedtimes and wake times strengthen circadian rhythms and improve metabolic and cardiovascular health. Sleep fragmentation (waking frequently) also reduces restorative benefits even if total hours look sufficient.

How to tell if you’re getting the “right” amount

Use these practical indicators, not just the clock:

You fall asleep within ~20 minutes of going to bed.
You wake up naturally around the same time most mornings.
You feel alert, focused, and energetic through the day without regular naps or caffeine reliance.
You don’t experience excessive daytime sleepiness or frequent microsleeps (brief uncontrollable sleep episodes).

If you’re regularly nodding off during meetings, driving, or while reading, you likely need more/better sleep or medical assessment.

Tips to improve sleep duration and quality (evidence-based strategies)

Aim for consistent sleep times. Go to bed and wake up at the same time every day (including weekends) to stabilize circadian rhythms.
Create a wind-down routine. 30–60 minutes before bed: dim lights, avoid stimulating screens, and do relaxing activities (reading, light stretching, breathing).
Make the bedroom sleep-friendly. Cool, dark, quiet, and comfortable bedding supports deeper sleep.
Limit caffeine, alcohol, and heavy meals near bedtime. Caffeine can disrupt sleep up to 6–8 hours; alcohol fragments sleep.
Get daytime light and physical activity. Morning sunlight and regular exercise (not right before bed) improve sleep timing and depth.
Avoid long daytime naps if you have trouble sleeping at night; keep naps short (20–30 minutes) and early in the afternoon.
Evaluate medications and health conditions. If you have persistent excessive sleepiness, long sleep, or poor sleep quality, consult a clinician — conditions like sleep apnea, restless legs, depression, thyroid disease, or medications can be causes.

When to see a doctor

Seek medical advice if you:

Fall asleep unintentionally during daytime activities.
Snore loudly, gasp, or stop breathing at night (possible sleep apnea).
Have long-term insomnia (trouble falling or staying asleep) despite good sleep habits.
Experience sudden and unexplained changes in sleep duration (sleeping much more or less than usual).
A clinician can screen for sleep disorders, mood disorders, or medical problems and refer you for sleep testing or therapy when needed.

Bottom line (actionable takeaway)

For most healthy adults, target 7–9 hours of sleep per night and make sure sleep is regular and restorative.
Too little sleep (<7 hours) is linked to elevated risks of heart disease, diabetes, obesity, impaired cognition, and higher mortality.
Regularly sleeping a lot (>9 hours) is associated with some risks and frequently signals an underlying problem — get evaluated if it’s persistent.
Prioritize sleep quality and regularity as much as raw hours. Small, consistent habits (regular schedule, wind-down routine, daylight exposure) produce outsized benefits.

Sources

Centers for Disease Control and Prevention — About Sleep; Recommended sleep amounts by age. CDC
American Academy of Sleep Medicine / Sleep Research Society — Joint consensus on recommended adult sleep duration. PMC
Itani O., et al. (2017) — Systematic review/meta-analysis: Short sleep duration and health outcomes. PubMed
Jike M., et al. (2018) — Long sleep duration and health outcomes (systematic review). ScienceDirect
Cappuccio FP., et al. (2010) — Sleep duration and all-cause mortality (systematic review). PMC
National Sleep Foundation / Sleep Foundation — Sleep duration guidance and practical tips. National Sleep Foundation+1
Semmelweis University coverage (2025) — Large-scale studies linking short/long sleep with stroke risk (summary of recent findings). Semmelweis Egyetem
National Heart, Lung, and Blood Institute (NHLBI) — How Much Sleep Is Enough? guidance for various ages. NHLBI, NIH