"I didn't eat anything after 8 pm. I slept the whole night. How come my blood sugar is 8.5 when I wake up?"
We get this question almost every week. And it's a fair one. If you haven't eaten for 10 or 12 hours, it feels like the reading should be at its lowest. For a lot of people, it's the opposite. High fasting glucose, the number you see first thing in the morning, is the worst one of the day.
Here's what's going on.
Your body makes its own sugar while you sleep
Most people think blood sugar only comes from food. It doesn't. Your liver stores sugar and releases it into your blood whenever your body thinks it needs fuel.
Between about 3 am and 8 am, your body starts getting ready to wake up. It releases a wave of hormones, mainly cortisol, growth hormone, and adrenaline. Those hormones tell the liver: release sugar, we're about to start the day.
This happens to everyone. It's called the dawn phenomenon. In a healthy body, the pancreas responds by sending out a little extra insulin, the sugar gets used, and fasting glucose stays around 4 to 5.5.
What high fasting glucose actually means
If your cells have become less sensitive to insulin, that morning sugar release doesn't get cleared. The liver dumps sugar in, insulin shows up, the cells don't respond properly, and the sugar sits in your bloodstream. You wake up, test, and see 8, 9, sometimes 10 or more. For comparison, see what counts as normal blood sugar levels in Malaysia.
So high fasting glucose isn't about what you ate last night. It's your body showing you how well it handles sugar when there's no food involved at all. In a way, it's the most honest number you'll get all day, which is exactly why doctors use fasting glucose to diagnose diabetes.
Three other things that push fasting glucose up
1. A big or late dinner. If dinner was heavy on rice or noodles and finished at 10 pm, your blood sugar may still be coming down from that meal when the dawn hormones kick in. The two stack on top of each other.
2. Poor sleep. Short sleep, broken sleep, or waking up several times to pee all raise cortisol. More cortisol means more sugar released from the liver. People who sleep badly tend to have higher fasting glucose the next morning.
3. A low in the middle of the night. This one surprises people. If you're on insulin or certain diabetes tablets, your sugar can drop too low around 2 or 3 am without waking you. For years this was blamed for high morning readings, the idea being that the body overshoots while correcting the low. But a 2022 study that tracked 2,600 people with type 2 diabetes overnight found no such rebound: if anything, a night-time low tends to leave the morning reading lower, not higher. The low itself still matters, because it's a safety issue, and it's worth mentioning to your doctor if your fasting readings swing a lot from day to day.
How to tell which one it is
Test at three points for a few nights: before bed, around 3 am, and when you wake up.
- Bed normal, 3 am normal, morning high: that's the dawn phenomenon.
- Bed high, 3 am high, morning high: dinner is the problem.
- Bed normal, 3 am low, morning high: the night-time low is the important finding here, not the morning number. Talk to your doctor about your evening medication.
Use the same glucose meter for all three readings so you're comparing like with like. If you're new to testing, our step-by-step guide on how to check blood sugar at home covers the basics.
What actually helps bring high fasting glucose down
Eat dinner earlier and lighter. Aim to finish by 8 pm, with the rice or noodle portion smaller than lunch. Protein and vegetables are fine.
Take a short walk after dinner. Ten to fifteen minutes is enough. Muscles use up sugar when they move, which lowers the amount your liver has stored for the morning.
Fix your sleep first. This is the one most people skip. Seven hours of unbroken sleep lowers cortisol, and lower cortisol means a gentler morning sugar release. If you're waking to pee two or three times a night, that's itself a sign of high sugar and worth addressing.
Improve how your cells respond to insulin. Everything above helps manage the morning surge. None of it changes the reason the surge isn't cleared, which is reduced insulin sensitivity. That's the part that needs long-term work, and it's the part that decides whether high fasting glucose becomes a permanent feature or a phase you got through.
The evening dose is the one that matters most for fasting glucose.
Related reading
- High Fasting Glucose but Normal After Meals? What That Pattern Means (And the Reverse)
- How to Lower High Fasting Glucose: 7 Things to Do Tonight for a Better Reading Tomorrow
- Diabetic Diet in Malaysia: Can You Still Eat Roti Canai, Nasi Lemak and Teh Tarik?
References
- Cleveland Clinic. Dawn Phenomenon. Cleveland Clinic Health Library, 2022.
- American Diabetes Association. Diabetes Diagnosis & Tests. diabetes.org, 2025.
- Gu C, et al. Metabolic Effects of Late Dinner in Healthy Volunteers – A Randomized Crossover Clinical Trial. Journal of Clinical Endocrinology & Metabolism, 2020.
- Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. The Lancet, 1999.
- Buffey AJ, et al. The Acute Effects of Interrupting Prolonged Sitting Time in Adults with Standing and Light-Intensity Walking on Biomarkers of Cardiometabolic Health: A Systematic Review and Meta-analysis. Sports Medicine, 2022.
- NHS. Type 2 diabetes – Symptoms. nhs.uk, 2025.
- Huang Y, et al. Confirmation of the absence of Somogyi effect in patients with type 2 diabetes by retrospective continuous glucose monitoring. International Journal of Endocrinology, 2022.
This article is for general information only and is not medical advice. Please consult your doctor before changing your diet or medication.