Warm morning scene with a rising sun and a clock pointing to the early hours. A gentle curve rises towards morning, illustrating the dawn phenomenon, the natural morning rise in blood sugar.
3–8 a.m.
Rise towards morning
The morning value often rises on its own – without any breakfast.
Fasting blood sugar – measured in the morning before the first food – is one of the most important reference values in metabolism. Alongside HbA1c and the OGTT, it’s one of the standard diagnostic measures.
Which values apply
In people without diabetes, the fasting value is normally below 100 mg/dl. The range 100–125 mg/dl is considered prediabetes, and from 126 mg/dl (confirmed on two days) diabetes.1 For people with diabetes, the ADA often gives a target corridor of about 80–130 mg/dl – to be set individually.2
The dawn phenomenon: the morning rise
Evidence level: established
In the early morning hours – roughly between 3 and 8 a.m. – the body releases more so-called counter-regulatory hormones: cortisol, growth hormone, glucagon and adrenaline.23 They prepare the body for waking, but at the same time signal the liver to release sugar into the blood and lower insulin action. With a healthy metabolism, more insulin simply offsets this rise. With insulin resistance or diabetes, this compensation is missing – and the fasting value rises.3
Three steps: in the early hours between about 3 and 8 a.m., counter-regulatory hormones such as cortisol, growth hormone and glucagon rise. These signal the liver to release sugar into the blood and simultaneously lower insulin action. With a healthy metabolism, more insulin offsets it. With insulin resistance or diabetes, the fasting value rises.
How the dawn phenomenon arises
The morning rise begins not in the blood but with the hormones
⏰
1 · Hormones rise
3–8 a.m.: cortisol,
growth hormone,
glucagon, adrenaline
🍖
2 · Liver releases sugar
The liver releases
stored glucose,
insulin action drops.
📊
3 · The morning value
Healthy: more insulin
offsets it. With resistance:
fasting value rises.
→
→
A rise of at least 20 mg/dl from the overnight low to the morning counts as a significant dawn phenomenon.
Don’t confuse it: the Somogyi effect
A rarer phenomenon is the Somogyi effect, in which an overnight hypoglycaemia leads to a rebound high in the morning. Because the countermeasures are opposite, the distinction matters. Medically it can be clarified with a measurement around 2–3 a.m.: if the value is low then, that points more to a Somogyi effect; if it’s already elevated, more to insufficient basal coverage.3
Key takeaways
- Fasting value: below 100 mg/dl normal, 100–125 prediabetes, from 126 (confirmed) diabetes.
- The dawn phenomenon is a natural morning rise in blood sugar driven by hormones.
- The liver releases sugar and insulin action drops – with resistance, the morning value rises.
- A rise of ≥20 mg/dl counts as significant.
- Distinguish from the rarer Somogyi effect – medically via a night-time measurement.
Sources
Sources as of: 21 Jul 2026.
- Diagnostic fasting thresholds (<100 / 100–125 / ≥126). American Diabetes Association. diabetes.org
- High morning blood glucose: dawn phenomenon vs. Somogyi; targets. American Diabetes Association. diabetes.org
- Dawn phenomenon mechanism: counter-regulatory hormones, hepatic glucose output. Review. ncbi.nlm.nih.gov
- Factors influencing the morning value: dinner timing, movement, sleep/cortisol. Summary. virtahealth.com