By Carol Kreider, MSN, APRN, FNP-C
Dawn Phenomenon:
Many people with diabetes notice a puzzling pattern: their blood sugar is higher first thing in the morning than it was at bedtime—even though they didn't eat overnight. This early-morning rise is called the dawn phenomenon and understanding it can take away a lot of frustration.
What It Is
The dawn phenomenon is a rise in blood glucose in the early morning hours (usually between about 3 a.m. and 8 a.m) that happens without an overnight low. It can occur in type 1 and type 2 diabetes, prediabetes, and even in some people with normal glucose control. It's common, affecting roughly 40-50% of people with type 2 diabetes, and can add about 0.4% to HbA1c
Why It Happens
In the hours before you wake, your body releases a wave of hormones (growth hormone, cortisol, and adrenaline) to prepare you for the day. These hormones tell the liver to release more glucose and make tissues temporarily less sensitive to insulin. In people without diabetes, the pancreas simply adds a little extra insulin to compensate. In diabetes, that response falls short, so glucose climbs. A landmark 1985 study showed that overnight surges in growth hormone are a primary driver (Campbell et al., New England Journal of Medicine, 1985; Wang et al., Acta Diabetologica, 2026).
Not the Same as the Somogyi Effect:
- Dawn phenomenon: morning high with no overnight low.
- Somogyi effect: morning high that follows an overnight low.
The best way to tell them apart is to look at overnight glucose, ideally with a continuous glucose monitor (CGM) (Barua et al., Scientific Reports, 2024).
What Can Help
Management should be individualized with your care team, but studied strategies include:
- Adjusting medication or insulin timing to better cover early-morning hours.
- Morning exercise before breakfast, which reduced glucose spikes in one study
- Improving sleep quality, since poor sleep is linked to a stronger dawn effect
If your morning numbers are consistently high, bring CGM data to your care team for review
For general education and is not a substitute for individualized medical advice.