The Dawn Phenomenon: Why Is My Morning Plasma Glucose (Blood Sugar) High?

Chapter 19 · Vihang Rahul Vasa

If you ever find that your fasting morning plasma glucose (blood sugar) is surprisingly high despite eating right the night before, do not panic and do not blame yourself. This is a well-known phenomenon called the Dawn Phenomenon, and it happens to many people living with diabetes.

In the early morning hours, typically between 3 AM and 8 AM, your body naturally releases hormones such as cortisol, glucagon, and growth hormone to prepare you for the day ahead. These hormones signal the liver to release stored glucose into the bloodstream, causing a rise in plasma glucose (blood sugar) even though you have not eaten anything. In people without diabetes, the body compensates by producing extra insulin. In people living with diabetes, this compensation is impaired, resulting in higher fasting readings.

But a high morning number is not always the dawn phenomenon. There are other everyday reasons: a night-time medicine that wears off before morning, the timing or dose of your medicines, a carbohydrate-heavy snack close to bedtime, an illness brewing, a stressful day, a broken night’s sleep, or a low in the night that your body over-corrected (the Somogyi effect, Chapter 18). Only the pattern tells which it is, and that is why one high reading is never a reason to change a dose on your own. Note it, and let your doctor read the pattern.

Knowing that this exists prevents unnecessary frustration and self-blame. If you notice a consistent pattern of elevated morning readings, discuss it with your diabetes specialist: there are specific strategies and medication adjustments that can help manage it effectively.

Illustration: Chapter 19 illustrated summary. The dawn phenomenon diagram links early-morning hormones, preparation for the day, liver release of stored glucose and a morning glucose rise.

Chapter 19 The dawn phenomenon diagram links early-morning hormones, preparation for the day, liver release of stored glucose and a morning glucose rise. Other causes are possible. CGM helps investigate overnight patterns, with doctor-led review.

Chapter at a glance: an AI-generated illustration to be read with the chapter, not instead of it. The people shown are not real.