What does too little sleep do to the body?
The short answer
In the short term, poor sleep affects mood, concentration, appetite and blood sugar. Over many years, regularly sleeping too little is linked with a higher risk of obesity, diabetes, heart disease and early death. Most adults need seven to nine hours.
Choose your depth
In the short term, poor sleep affects mood, concentration, appetite and blood sugar. Over many years, regularly sleeping too little is linked with a higher risk of obesity, diabetes, heart disease and early death. Most adults need seven to nine hours.
Choose Detailed for the fuller picture, or Scientific for mechanisms and study data.
During sleep the body carries out important restorative processes, memories are consolidated and hormones that influence appetite and blood sugar are regulated.
After a few bad nights
- Slower reactions and poorer concentration
- More irritability and anxiety
- More hunger, especially for sugary foods
- Less efficient blood sugar control
Over years
A meta-analysis of studies following 1.38 million people found that those who habitually slept too little had a 12 per cent higher risk of dying during follow-up. Short sleep is also linked with weight gain, type 2 diabetes and high blood pressure.
What helps
- A regular bedtime and waking time, even at weekends
- Morning daylight and dimmer light in the evening
- No caffeine after mid-afternoon
- A cool, dark, quiet bedroom
Loud snoring with daytime sleepiness can signal sleep apnoea, which needs a doctor's assessment.
Cappuccio et al. (2010) pooled 16 prospective cohorts (1,382,999 participants, 112,566 deaths): short sleep RR 1.12 (95% CI 1.06 to 1.18), long sleep RR 1.30 (1.22 to 1.38). Short sleep may be causal through autonomic, endocrine and inflammatory pathways, while long sleep is more likely a marker of comorbidity.
Melatonin, secreted by the pineal gland in darkness, signals biological night. Exogenous melatonin is best supported for circadian misalignment such as jet lag (Herxheimer and Petrie, Cochrane 2002), where timing relative to the target bedtime determines effect.
What we know
- Most adults need seven to nine hours.
- Chronic short sleep is associated with poorer long-term health.
- Consistent timing improves sleep quality.
What remains uncertain
- How much of the association is caused by sleep itself.
- How individual sleep needs vary.
The evidence
Related ingredients
Sources
- Cappuccio FP, D'Elia L, Strazzullo P, Miller MA. Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies. Sleep. 2010;33(5):585-592.
- Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev. 2002;(2):CD001520.
Last updated 15 October 2026.
This is educational content and does not replace advice from a qualified doctor. If you have symptoms or take medicines, please speak to your doctor before making changes.
