Why Is Blood Sugar High in the Morning but Normal at Night?

You may go to bed with a normal reading and wake up with a higher one. Why does this happen?

Your Morning Reading Can Be Different

Blood glucose can change overnight even when you have not eaten. Hormones, insulin activity, sleep and other factors can affect your morning reading.

1. The Dawn Phenomenon

In the early morning, natural hormones such as cortisol and growth hormone can signal the liver to release more glucose.

In people with diabetes, the body may not produce enough insulin or may be more resistant to insulin, allowing glucose to rise.

2. Evening Food Can Matter

A large evening meal or carbohydrate-rich bedtime snack may contribute to higher glucose later during the night or the following morning.

3. Overnight Insulin Changes

If insulin or diabetes medicine does not provide enough coverage overnight, blood glucose may gradually rise before breakfast.

Never change insulin or medication doses on your own.

4. Sleep May Play a Role

Poor or disrupted sleep can affect hormones and glucose regulation. If morning highs happen repeatedly, look at your overall sleep and daily routine.

5. Check the Pattern

One unusual reading does not necessarily explain what is happening. Track your readings over several days and discuss repeated patterns with your healthcare professional.

Could It Be a Nighttime Low?

A nighttime low followed by a morning high has historically been called the Somogyi effect. However, newer evidence has questioned how commonly this explains morning highs.

A healthcare professional can help interpret your overnight glucose pattern.

What Can You Do?

Keep a simple record of bedtime and morning glucose readings, evening meals, snacks, sleep and activity. This can help reveal patterns.

If morning highs continue, speak with your diabetes care team before changing medication.

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