Sleep – the foundation of metabolic health
Sleep is not wasted time. While you sleep, your body repairs itself – hormones, the immune system and metabolism are all at work. Regularly sleeping less than 6 hours is as harmful as a poor diet. It raises insulin resistance (when cells respond poorly to insulin and blood sugar stays high), the stress hormone cortisol, appetite and inflammation.
- 1 week of less than 6 hours of sleep = your body responds to insulin almost 40% worse
- During deep sleep and REM (dream) sleep, the brain clears out waste
- Cortisol, melatonin and growth hormone shift together with sunlight
Why sleep matters for the whole body
During sleep the body doesn’t ‘switch off’ – the opposite happens. Processes that can’t happen while you’re awake kick in. The brain clears out metabolic waste through the glymphatic system (a network of channels that ‘flushes’ the brain during sleep). In deep sleep, growth hormone repairs tissue. In REM (dream) sleep, the brain locks in memories and processes emotions.
Sleep quality matters as much as how long you sleep. 8 hours of broken sleep with little deep sleep is worse than 7 hours of calm, unbroken sleep.
Early signs of poor sleep
- Waking up without an alarm feels hard; morning grogginess lasts more than 30 minutes
- Waking up around 3–4 am (this can be an early rise in cortisol, the stress hormone)
- It takes more than 30 minutes to fall asleep – or, on the other hand, you fall asleep in under 5 minutes, a sign of serious sleep debt
- Night sweats or an uncomfortable urge to move your legs (restless legs syndrome, RLS)
- Snoring or pauses in breathing during sleep (may point to sleep apnea – brief pauses in breathing while asleep)
- Craving sweets in the afternoon, evening snacking
- Handling stress feels harder, you’re irritable, focus is difficult
Sleep and insulin sensitivity
In a well-known study (Van Cauter & Spiegel, The Lancet, 1999), healthy men had their sleep cut to 4 hours a night for 6 nights. Their ability to process sugar (glucose tolerance) dropped by 40% – close to a pre-diabetic level. It returned to normal once normal sleep resumed.
Every hour of lost sleep raises insulin and appetite the next day: the fullness hormone leptin drops, and the hunger hormone ghrelin rises. That’s why people who sleep too little often eat 300–500 extra calories without noticing.
Cortisol and your body clock (circadian rhythm)
- Cortisol (the stress and alertness hormone) should peak in the morning, about 30 minutes after waking
- In the evening, after 8 pm, cortisol should drop – otherwise it’s harder to fall asleep
- Blue light from screens in the evening cuts melatonin (the sleep hormone) by 50–90%
- Natural morning light (10 minutes in the first hour after waking) resets your body clock
Four simple steps to better sleep
Before turning to sleeping pills, try these four steps consistently for 2–4 weeks. For most people, that’s enough to see a real improvement.
Light
Get 10–20 minutes of natural light in the first hour after waking. In the evening, use night mode on screens, and dim the lights after 9 pm. Keep the bedroom fully dark.
Temperature and routine
Keep the bedroom at 17–19 °C. Wake up and go to bed at the same time (within 30 minutes), including weekends. Eat dinner at least 2–3 hours before bed.
Supplements for sleep (only when needed)
Before adding supplements, get your light exposure, caffeine, alcohol, workout timing and stress under control. Once those are in place, supplements work much better.
- Magnesium – studied in the context of relaxation and sleep quality
- L-theanine – studied in the context of evening anxiety
- Glycine (3 g) – slightly lowers body temperature and helps you fall asleep faster
- Apigenin (chamomile extract) – a plant compound with a calming effect
- Melatonin – suitability, dose and duration are decided by a physician
- Ashwagandha – studied in the context of stress tolerance; not suitable for everyone, including thyroid disease and pregnancy
Meal timing and sleep
Eating less than 2 hours before bed raises overnight blood sugar and insulin, and reduces deep sleep and growth hormone release. If your last meal is around 7–8 pm, sleep quality improves for most people within a few weeks.
Very strict calorie restriction (under 500 kcal/day) can worsen sleep in the first weeks – give your body 2–3 weeks to adjust.
Labs that help explain poor sleep
- Salivary cortisol through the day (4 samples) – shows your daily stress-hormone rhythm
- Fasting glucose and insulin, HOMA-IR – a snapshot of metabolic health
- Ferritin and TIBC – low iron can cause restless legs and broken sleep
- TSH and free T3 – thyroid hormones affect body temperature at night and sleep
- Vitamin D, magnesium, zinc – commonly low
- If you snore and have breathing pauses, consider a sleep-apnea test (can be done at home)
Go deeper: sleep and circadian webinars
Recorded material on sleep science, the cortisol rhythm and practical interventions.
Frequently asked questions
Go deeper: related material
Guides
Webinars
Courses
Related topics
Metabolic health is interconnected – explore the other deep-dives:
Insulin resistance
The root of metabolic disease – 5–10 years before diabetes appears.
ReadOverweight
Why calorie counting fails – hormones, insulin, leptin and adipose tissue.
ReadVagus nerve
The rest-and-repair system – digestion, heart, inflammation, stress.
ReadCholesterol & ApoB
Expanded lipid panel – ApoB, Lp(a), homocysteine, A vs B phenotype.
ReadChronic inflammation
The ‘silent fire’ behind cardiovascular disease, diabetes and autoimmunity.
ReadLow-carb and keto
Carbohydrate restriction – IR, T2D, fatty liver, metabolic syndrome.
ReadChronic sleep loss affects the whole body
If sleep has been poor for more than 3 months, it’s worth reviewing the metabolic and hormonal context. In a consultation we look at the relevant labs and build a plan.
Booking information and contactThis page is educational and general in nature. It is not personal medical advice, a diagnosis or a treatment plan. Discuss changes to your health, medication or supplements with your own doctor.