Short sleep does more than leave us feeling tired. It measurably changes how the body handles blood sugar, and it does so after a single night.
Nine healthy adults spent one night in a sleep lab with eight hours in bed, and another with four. Nothing else about their lives changed.
After the short night, their bodies handled glucose measurably worse : their livers released more glucose than they should have while insulin was working to suppress it, and their muscles took up less of it. Nine people is a small group, though insulin sensitivity was measured by clamp, the reference method, rather than estimated from a blood draw.
How a week of bad sleep affected glucose
Twenty healthy men aged 20 to 35 spent twelve days in a research unit. For the first stretch they had ten hours in bed a night. Then they had five hours a night for a week, while their food and exercise were kept the same.
Insulin sensitivity fell by 20% on average . The spread between individuals was wide, wider than the average itself, so some men were affected far more than others and a few barely at all. The direction was consistent enough to reach significance across the group. A separate group of 23 young men, held to four hours in bed for five nights, came out with raised insulin and a raised insulin-to-glucose ratio .
That is the same metabolic direction as early insulin resistance , produced in a week, in young healthy people, by nothing but a shorter night.
The effects of long-term poor sleep
A longer experiment put healthy adults through more than five weeks in a controlled lab. Three of those weeks combined 5.6 hours of sleep per 24 hours with a schedule built on 28-hour days, which scrambles the body clock the way rotating shifts do.
Their post-meal glucose climbed, and their resting metabolic rate fell . The cause was traced to the pancreas failing to release enough insulin, rather than the tissues ignoring it.
It took nine days of recovery sleep on a normal schedule for markers to return to where they started. If your work puts you on rotating shifts , that combination of short sleep and a moving clock is the one the study was built to imitate.
Why sleep affects glucose
Your body regulates glucose on a 24-hour schedule. Insulin sensitivity, cortisol and growth hormone all follow a circadian rhythm anchored by when you sleep and wake, and that clock keeps its own time whether or not your schedule agrees with it.
Cortisol is the clearest link. When eleven young men were held to four hours in bed for six nights, their glucose tolerance dropped, their evening cortisol rose and their sympathetic nervous system activity increased . Cortisol prompts the liver to make glucose, so an evening rise arrives at exactly the wrong hour.
How long you sleep is only part of it. Our own analysis of 105,196 nights of paired ring and CGM data found that how consistent your sleep length is carries its own association with overnight glucose, separate from how long you sleep. Our science pages go further into what glucose does overnight .
Key takeaways
Protect the duration first. Every study above changed one thing, the number of hours, and every one of them moved glucose. Nothing else in this list has that weight of evidence behind it.
Keep your sleep length steady across the week. A late Friday and a long Saturday morning change how much sleep you get on both nights.
Fix the room before you fix anything else. Quiet, dark, cool, and no screens within reach of the bed. Our guide to sleep hygiene covers the hour before bed in more detail.
Leave a gap after eating and drinking. Large meals, caffeine and alcohol close to bedtime all disturb the night, and alcohol in particular raises your heart rate while you sleep.
Move during the day. Physical activity shortens the time it takes to fall asleep and deepens what follows.
Recovery sleep counts. The five-week study found both measures back to baseline after nine days of normal sleep. A bad fortnight is not permanent.
If you wear a CGM, the overnight window is where any of this will show up first, within the limits of what the sensor can measure . Over a week, variability and time in range are the two numbers that tell you something a single night cannot.
Night-time glucose spikes have several causes, and short sleep is one worth ruling in or out. The same goes for waking at 3am .
References
- Donga E, van Dijk M, van Dijk JG, et al. A single night of partial sleep deprivation induces insulin resistance in multiple metabolic pathways in healthy subjects. J Clin Endocrinol Metab. 2010;95(6):2963-2968. PMID 20371664
- Buxton OM, Pavlova M, Reid EW, Wang W, Simonson DC, Adler GK. Sleep restriction for 1 week reduces insulin sensitivity in healthy men. Diabetes. 2010;59(9):2126-2133. PMID 20585000
- Buxton OM, Cain SW, O’Connor SP, et al. Adverse metabolic consequences in humans of prolonged sleep restriction combined with circadian disruption. Sci Transl Med. 2012;4(129):129ra43. PMID 22496545
- Schmid SM, Hallschmid M, Jauch-Chara K, et al. Prolonged sleep restriction affects glucose metabolism in healthy young men. Int J Endocrinol. 2010;2010:108641. PMID 20414467
- Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. Lancet. 1999;354(9188):1435-1439. PMID 10543671
Disclaimer. The contents of this article are for general information and educational purposes only. It neither provides medical advice nor intends to substitute professional medical opinion on the treatment, diagnosis, prevention or alleviation of any disease, disorder or disability. Always consult your doctor or a qualified healthcare professional about your health and before undertaking a new healthcare regimen, including any dietary or lifestyle changes.
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