Sleep and Blood Sugar: How Rest, Apnea and Shifts Matter

Sleep and blood sugar affect each other. In a lab study of 9 healthy adults one night of about 4 hours of sleep cut insulin sensitivity by about 25%.^[1] Over years the pattern shows up in big studies too. This guide covers what short sleep, sleep apnea and shift work do, why glucose can rise overnight, and how much sleep to aim for. It reports what the studies found and where they fall short.

This guide is general education. If you use insulin or other glucose medicines, follow the plan your diabetes team gave you.

How are sleep and blood sugar linked?

Short sleep seems to make the body respond less well to insulin. In 11 young men, six nights of 4 hours in bed gave weaker glucose tolerance than six nights of 12 hours in bed.^[9]

One night can be enough in a lab. Nine healthy adults slept about 226 minutes in one night and about 454 minutes in another. After the short night the glucose infusion rate in a clamp test fell by about 25%.^[1] Their fasting glucose did not change.^[1]

Be careful with these results. Both groups were healthy and small, and neither reported a change in HbA1c. We cannot say that one bad night raises your HbA1c.

Does lack of sleep raise blood sugar?

Short sleep is linked with a higher chance of type 2 diabetes. A meta-analysis of 482,502 people found about 9% higher relative risk for each hour of sleep below 7 hours.^[3] The smallest risk sat at 7 to 8 hours.^[3]

What the main sleep studies found

Long sleep was linked with higher risk too, so do not cut your sleep short to fix a number.^[3] Our stress and glucose guide covers a related topic.

Why does blood sugar rise while sleeping?

A small rise in blood sugar before breakfast, without eating, is called the dawn phenomenon. Among 248 people with type 2 diabetes not using insulin, glucose rose a median of 16 mg/dL (0.9 mmol/L) from the night low to before breakfast.^[8] That study does not name a cause. For type 1 diabetes, one expert commentary calls night-time growth hormone spikes the most likely mechanism, and its authors report honoraria from drug makers.^[10]

The size of the rise matters for the bigger picture. In that study its effect on HbA1c was about 0.4 percentage points (about 4 mmol/mol).^[8] It was a French clinic study from 2013, so drug classes have changed since. Our guide to the dawn phenomenon explains the morning side in more detail.

Blood sugar during sleep can also fall

Night lows are the opposite problem. NIDDK says glucose can drop while you sleep and stay low for several hours, and you may not wake or notice symptoms.^[6] Clues include nightmares, sweat that dampens your sheets, and feeling tired or confused after waking.^[6]

Low glucose can also disturb your sleep and make you less alert to lows the next day.^[6] Night lows are more likely if you use insulin or a sulfonylurea such as gliclazide or glimepiride. Low blood sugar usually means below 4 mmol/L (72 mg/dL) in the UK or below 70 mg/dL (3.9 mmol/L) in the US.^[11][6] Tell your GP or diabetes team if you suspect night lows, and do not change a dose on your own.^[6][11] In the UK, the NHS says to call 999 if someone may have very low blood sugar and is not responding normally or is unconscious, and a glucagon injection is not available or you do not know how to use it, or they have not recovered within 10 minutes of a glucagon injection, or they have been drinking alcohol.^[11] In the US, NIDDK says to call 911 right away after giving glucagon or if there is no glucagon kit.^[6] Our bedtime routine guide has practical steps for steadier nights.

Is sleep apnea linked to diabetes?

Yes, and it is common in people with type 2. The ADA estimates that 55% of people with type 2 diabetes have obstructive sleep apnea.^[12] In 306 obese US adults with type 2 who were in a weight-loss trial, over 86% had sleep apnea by the study definition. One author is a scientific consultant to a CPAP maker, Philips-Respironics.^[13] Read the exact share as group dependent.

The NHS describes sleep apnea as breathing that stops and starts during sleep. It lists type 2 diabetes among the problems it can lead to if it is not managed.^[14] The ADA suggests screening for sleep disorders in people with diabetes.^[12] See your GP if you snore loudly or wake gasping. Sleep apnea and diabetes often go together, so mention both.

Does CPAP help blood sugar?

The evidence is mixed. A meta-analysis of 11 randomised trials with 964 people found that HbA1c fell by 0.24 percentage points (about 2.6 mmol/mol) on average with CPAP against inactive controls.^[4] The authors call the evidence from single trials controversial, and one author discloses consulting fees from drug companies.^[4]

A sham-controlled trial of 98 adults looked again. After 12 weeks HbA1c had fallen 0.26 percentage points (about 2.8 mmol/mol) with CPAP and 0.24 (about 2.6 mmol/mol) with sham, with no sustained difference overall.^[5] The NHS lists benefits such as better breathing and less tiredness, and it does not name blood sugar.^[14] CPAP is prescribed for sleep apnea, not for glucose, so any change in how you use it belongs with your sleep clinic.

How many hours should a person with diabetes sleep?

Aim for at least 7 hours a night. The AASM and Sleep Research Society say adults should sleep 7 or more hours on a regular basis.^[2] NIDDK tells most adults to aim for about 7 to 8 hours each night.^[15] If you have searched for how much sleep should diabetics get, the answer is the same: these are general adult figures, not a separate rule for diabetes.

1. Aim for about 7 to 8 hours of sleep a night on a regular schedule.^[2][15]
2. Tell your GP or diabetes team if you snore loudly, wake gasping or feel very sleepy in the day.^[12][14]
3. Report signs of night lows, such as damp sheets, nightmares or waking confused, especially if you use insulin or a sulfonylurea such as gliclazide or glimepiride.^[6][11]
4. Bring your shift schedule to your clinic appointments so your team can match your meals and medicine timing to your sleep hours.^[12]

Does shift work change sleep and blood sugar?

It can. The ADA says people with diabetes who do shift work have a higher risk of circadian rhythm disorders, which are associated with elevated A1C.^[12] In pooled observational studies, shift work went with a 10% higher relative risk of type 2 diabetes (RR 1.10, 95% CI 1.05 to 1.14), which shows an association and not cause.^[7]

Ask your care team how to plan meals, medicines and checks around your shifts. The ADA advises that clinicians look at sleep, shift schedules and days off together.^[12] For fitting activity around shifts, see our exercise and glucose guide.

Questions to ask your diabetes team

• Could the dawn phenomenon or night lows explain my morning glucose readings?^[6][8]
• Should I be screened for obstructive sleep apnea?^[12][14]
• How should I adjust my medicine timing or bedtime snack when working night or rotating shifts?^[6][12]
• Should I check my blood sugar during the night if I wake up sweating or with a headache?^[6]

Frequently asked questions

Does one bad night of sleep raise blood sugar?

Not clearly. In 9 healthy adults one night of about 4 hours cut insulin sensitivity by about 25%, yet fasting glucose did not change. No study here shows that one night moves HbA1c.^[1]

How much sleep do adults need?

At least 7 hours a night on a regular basis, say the AASM and Sleep Research Society. NIDDK says most adults should aim for about 7 to 8 hours. Talk to your GP or primary care team if you feel you sleep too little or too much.^[2][15]

Does CPAP improve blood sugar?

Results are mixed. A pooled analysis of 11 trials found HbA1c fell by 0.24 percentage points (about 2.6 mmol/mol) on average. A 12 week sham-controlled trial of 98 adults found no sustained difference between CPAP and sham.^[4][5]

Can low blood sugar happen while I sleep?

Yes. NIDDK says glucose can drop during sleep and stay low for several hours, often without waking you. Damp sheets, nightmares or feeling confused on waking are clues. Tell your GP or diabetes team if it happens.^[6]

Where to go next

Steady sleep habits, checking for sleep apnea and planning for night lows or shift changes can make overnight blood sugar easier to discuss with your care team.

• The bedtime routine for stable overnight blood sugar, for snacks, timing and night checks.
• The dawn phenomenon, for why numbers climb in the early morning.
• Is Diabec legit?, for what is in our supplement and what it does not do.

Note: If you are pregnant, breastfeeding, or considering giving any supplement or herbal product to a child, consult your healthcare provider before making any changes to your diet, supplement routine, or prescribed medications.