Waking up to unexpectedly high blood sugar levels—even without having eaten—can be both puzzling and frustrating.

For many people with diabetes or prediabetes, this early-morning rise is a familiar challenge. The main cause? A process known as the dawn phenomenon.

Let’s take a closer look at what it is, why it happens, and how you can keep it under control.

What is the Dawn Phenomenon?

The dawn phenomenon is a natural rise in blood sugar that typically happens between 2 a.m. and 8 a.m. It occurs in everyone, but for those with diabetes, the effect is stronger and more difficult to manage.

Why Does It Happen?

Your body follows a built-in 24-hour schedule called the circadian rhythm. As morning approaches, it begins preparing to wake you up by releasing certain hormones:

• Cortisol

• Growth hormone

• Epinephrine (adrenaline)

• Glucagon

These hormones tell the liver to release stored glucose into the bloodstream, providing the energy needed to start the day. In people without diabetes, the pancreas balances this rise by producing extra insulin.

For those with diabetes or insulin resistance, the body either doesn’t make enough insulin or the insulin isn’t as effective. The result is a noticeable and prolonged rise in blood sugar.

Signs You Might Have the Dawn Phenomenon

• Elevated blood sugar in the morning (fasting glucose)

• Normal or low glucose before going to bed

• Feeling tired, thirsty, or mentally foggy upon waking