Understanding the Causes and How to Take Action

Waking up with high blood sugar can feel frustrating—especially if you thought you were doing everything right the day before.
Morning blood sugar (also called fasting glucose) is an important health marker for anyone managing diabetes.
But when those numbers are higher than expected, it’s important to understand why—and how to respond.

In this article, we’ll cover:

• Why fasting blood sugars can rise overnight
• Differences based on your type of diabetes
• Practical steps to bring fasting glucose under control

Why Fasting Blood Sugar Can Be High

Several factors can cause high blood sugar first thing in the morning:

1. The Dawn Phenomenon

The dawn phenomenon is a natural rise in blood sugar. It occurs in the early morning hours, usually between 2:00 AM and 8:00 AM.
Your body releases hormones like cortisol, growth hormone, and adrenaline during this time. These hormones prepare you to wake up and start the day.
These hormones signal the liver to release stored glucose into the bloodstream. In people with diabetes, this can lead to higher-than-normal fasting glucose.

Reference: Monnier L, Colette C. (2015). Circadian rhythms, glucocorticoids and diabetes mellitus: from physiology to pathophysiology. Diabetes & Metabolism. https://doi.org/10.1016/j.diabet.2015.04.001

2. The Somogyi Effect (Rebound Hyperglycemia)

The Somogyi effect happens when blood sugar drops too low during the night (hypoglycemia). This triggers the body to release hormones that overcorrect and raise blood sugar too high by morning.
This is more common in people who take insulin or certain medications.

3. Inadequate Evening Medication or Insulin

If your insulin dose or diabetes medications in the evening are not enough, blood sugar can slowly rise overnight.

4. Late-Night Eating

Eating a large meal or high-carbohydrate snack before bed can lead to elevated glucose levels overnight. This is especially true if digestion slows down while you sleep.

What to Do: A Step-by-Step Guide

Here’s how to handle high fasting blood sugar, depending on your situation:

If You Have Type 1 Diabetes

• Check overnight patterns: Use a continuous glucose monitor (CGM) if possible. Alternatively, check manually at 2–3 AM. This can help you see if you are dropping low (Somogyi effect) or gradually rising (dawn phenomenon).
• Adjust basal insulin: Discuss with your healthcare provider about changing your long-acting (basal) insulin. This will better match your body’s needs overnight.
• Evening snack strategy: If prone to lows overnight, consider having a small, balanced snack. Include protein and healthy fat before bed.

Reference: Diabetes Control and Complications Trial Research Group. (1993). The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. New England Journal of Medicine. https://doi.org/10.1056/NEJM199309303291401

If You Have Type 2 Diabetes

• Monitor trends: Keep a blood sugar log for several days to notice patterns.
• Review evening habits: Avoid high-carb meals or snacks before bed. Focus on balanced meals with lean protein, fiber, and healthy fats.
• Medication adjustment: You may need changes in oral medications, GLP-1 receptor agonists, or evening basal insulin.
• Increase evening activity: A short walk after dinner can help lower overnight blood sugar.

Reference: American Diabetes Association. (2024). Standards of Care in Diabetes – 2024. Diabetes Care. https://doi.org/10.2337/dc24-S001

If You Have Type 1.5 Diabetes (LADA)

Type 1.5 diabetes (Latent Autoimmune Diabetes in Adults) often starts with features of type 2 diabetes. However, it progresses toward insulin dependence over time.

• Assess insulin needs: Many with LADA eventually require basal insulin to control fasting sugars.
• Track trends carefully: LADA can be unpredictable. It’s critical to track blood sugars frequently. Work with a healthcare provider on a personalized plan.
• Avoid assuming it’s lifestyle only: Medication or insulin needs often change over time.

Reference: Naik RG, Brooks-Worrell BM, Palmer JP. (2009). Latent autoimmune diabetes in adults. Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/jc.2009-0633

If You Have Gestational Diabetes

• Manage bedtime snacks carefully: A small snack with protein and complex carbs is important. It may help prevent overnight liver glucose release. You can try options like Greek yogurt with berries.
• Monitor fasting goals: Fasting glucose targets are typically below 95 mg/dL in pregnancy (but follow your provider’s specific goals).
• Medication adjustments: If diet alone isn’t enough, you may need nighttime insulin or oral medications.
• Prioritize stress reduction: Stress hormones can also worsen fasting numbers during pregnancy.

Reference: American College of Obstetricians and Gynecologists (ACOG). (2018). Practice Bulletin No. 190: Gestational Diabetes Mellitus. https://doi.org/10.1097/AOG.0000000000002501

General Tips for Managing High Morning Blood Sugar

• Stay consistent with bedtimes and mealtimes
• Avoid heavy meals or high-sugar snacks close to bedtime
• Manage stress before bed (deep breathing, light stretching, relaxation techniques)
• Check blood sugar once overnight to identify dawn phenomenon vs. rebound highs
• Talk to your healthcare provider about adjusting medications or insulin doses
• Stay hydrated — dehydration can concentrate blood sugars

When to Contact Your Healthcare Provider

You should call your doctor if:

• Fasting blood sugars are consistently above your target range (for most people, >130 mg/dL upon waking)
• You experience frequent lows at night or symptoms of hypoglycemia (sweating, shaking, confusion)
• You’re pregnant and your fasting blood sugars are elevated despite dietary changes
• You’re unsure how to adjust your medications safely

Never change your insulin or medication doses without medical advice.

Final Thoughts

High fasting blood sugars can be frustrating—but they are common and manageable with the right strategies.
It is important to determine if the issue is the dawn phenomenon, the Somogyi effect, or lifestyle habits. This understanding can help you and your healthcare team create an action plan that works.

Whether you have Type 1, Type 2, LADA (Type 1.5), or gestational diabetes, the key is to track trends, adjust thoughtfully, and stay proactive.

References

1. Monnier L, Colette C. (2015). Circadian rhythms, glucocorticoids and diabetes mellitus: from physiology to pathophysiology. Diabetes & Metabolism. https://doi.org/10.1016/j.diabet.2015.04.001
2. Diabetes Control and Complications Trial Research Group. (1993). The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. New England Journal of Medicine. https://doi.org/10.1056/NEJM199309303291401
3. American Diabetes Association. (2024). Standards of Care in Diabetes – 2024. Diabetes Care. https://doi.org/10.2337/dc24-S001
4. Naik RG, Brooks-Worrell BM, Palmer JP. (2009). Latent autoimmune diabetes in adults. Journal of Clinical Endocrinology & Metabolism. https://doi.org/10.1210/jc.2009-0633
5. American College of Obstetricians and Gynecologists (ACOG). (2018). Practice Bulletin No. 190: Gestational Diabetes Mellitus. https://doi.org/10.1097/AOG.0000000000002501

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