Blood sugar levels were perfectly fine before bedtime last night, yet upon waking up, the numbers on the glucose meter were alarmingly high.

"Doctor, I've been very strict with my diet. My blood sugar was only 6.8 before bed last night, so why did it jump to 9.5 this morning on an empty stomach?" This is a recurring concern many individuals with diabetes express during clinic visits. Persistently high fasting blood sugar levels, like a stubborn mountain peak, are not only disheartening but also often indicate that treatment plans may need adjustment.

Behind this phenomenon lies a key yet frequently overlooked "physiological alarm clock"—the dawn phenomenon. However, it is certainly not the only culprit.

01 The Dawn Phenomenon: The Body’s “Morning Mobilization”

What is the Dawn Phenomenon?

This refers to a phenomenon in which individuals with diabetes experience a gradual increase in blood glucose levels from the nighttime (typically in the latter half of the night) to the early morning hours, without experiencing hypoglycemia. It is not a disease, but a common physiological response.

Why Does It Occur?

During the dawn period (approximately 3 a.m. to 8 a.m.), the human body secretes various "counterregulatory hormones," such as:

Growth Hormone

Cortisol

Glucagon

Adrenaline

Their purpose is to reserve energy for the upcoming day's activities, mobilizing the liver to produce more glucose. For normal individuals, the body secretes more insulin accordingly to maintain balance. However, for people with diabetes, insufficient insulin secretion or limited insulin action cannot suppress this "morning surge," leading to elevated fasting blood sugar levels.

⚠️ Key Identifying Points:

Blood sugar is well-controlled before bedtime.

No occurrence of hypoglycemia during the night.

Blood sugar begins to rise steadily and slowly from the latter half of the night until early morning.

02 High fasting blood sugar may also hide these 3 “hidden drivers”

When morning blood sugar raises a red flag, we must carefully differentiate because it may be a "mixed signal" from several completely different situations:

Reason One: Insufficient "Endurance" of Medication

This is one of the most common causes. The dose of glucose-lowering medication (especially medium- or long-acting insulin or oral medications) taken before dinner or at bedtime the previous day is insufficient, or the drug's effectiveness fails to cover the entire night. As a result, blood sugar becomes uncontrolled starting from the latter half of the night and gradually climbs.

How to distinguish? While the manifestation is similar to the Dawn Phenomenon, the core difference lies in whether the medication regimen aligns with the patient's needs. An assessment of the drug's duration of action should be conducted under the guidance of a physician.

⚠️ Reason 2: Somogyi Effect (Rebound Hyperglycemia)

！

Although fundamentally different from the Dawn Phenomenon, this condition is the most easily confused with it, and the management approach is entirely opposite!

What happens? An undetected hypoglycemic event occurs overnight (often in the early part of the night). In a self-preserving response, the body rapidly activates defense mechanisms, releasing a significant amount of counter-regulatory hormones, which causes blood glucose levels to rebound and spike in the morning—a "rebound" hyperglycemia.

The danger: If misdiagnosed as the dawn phenomenon or insufficient medication dosage and the dosage is increased, it can lead to more severe nighttime hypoglycemia, creating a vicious cycle that is extremely dangerous.

How to identify it? The key is to monitor blood glucose levels between 2-3 a.m. If blood glucose is low during this period (<3.9 mmol/L) but high in the early morning fasting state, it is likely the Somogyi effect.

Reason Three: The Influence from "Yesterday"

Improper Dinner/Snacking: Eating an excessively large, overly greasy dinner, or having excessive snacks before bedtime, causing the blood sugar-raising effect from food digestion and absorption to persist until morning.

Sleep and Emotions: Insomnia, staying up late, sleep apnea syndrome, or significant mental stress can all trigger the secretion of stress hormones, leading to elevated morning blood sugar.

Hidden Infections: Unnoticed mild inflammation in the body (such as periodontitis, urinary tract infections, etc.) can also cause an overall increase in blood sugar levels.

03 Precision "Case-Solving" in Just Two Steps

Facing high blood sugar in the morning, people with diabetes should not guess on their own or blindly adjust their medication! The scientific approach is:

Step One: Nighttime Blood Sugar Monitoring (The Gold Standard for Diagnosis)

This is the only method to differentiate between the Dawn Phenomenon and the Somogyi Effect. It is recommended, under a doctor's guidance, to conduct nighttime multi-point blood sugar monitoring, with key time points including:

Before Bed

2-3 AM (Most Critical!)

Early Morning Fasting

By examining these three key points, the truth about blood glucose changes becomes clear at a glance.

Step 2: Collaborate with your doctor to adjust the treatment plan

Bring detailed monitoring records—including blood glucose levels, diet, medication use, and sleep patterns—to your doctor for a joint analysis.

If it is the "dawn phenomenon": Under the guidance of your doctor, you may need to adjust the type or timing of evening medication (for example, switching to long-acting basal insulin analogs) or, if allowed, take the medication a bit earlier in the morning.

If it is the "Somogyi effect": It typically requires reducing the dose of hypoglycemic medication before dinner or bedtime, or adjusting the evening diet.

If it is due to insufficient medication: then the drug dosage or regimen needs to be optimized.

If it is due to lifestyle influences: then targeted adjustments in diet, improved sleep, and treatment of infections, among others, are necessary.

04 Your Morning Blood Glucose Action Guide

Do Not Panic: High fasting blood sugar is a "signal" that needs to be addressed, not the end of the world.

Do Not Adjust Medication on Your Own: This is the most important safety principle! Adjusting medication based on a misjudgment of the cause carries extremely high risks.

Learn to Record: Be a meticulous "detective" and record all potentially relevant details.

Trust the Professionals: Establish good communication with your endocrinologist. Use data to guide discussions and collaboratively develop a strategy.

Remember: the same "high" reading may stem from entirely different causes. Understanding the story your body silently tells overnight is the first step toward precise treatment and steady glucose control. When you and your doctor master the "topography" of your nighttime glucose levels, conquering that morning blood sugar peak is within reach.