High Morning Blood Sugar

by Mary
(Sacramento, Ca.)





QUESTION: My blood sugar is 112 mg/dL at bedtime but rises to 157 mg/dL by morning. It also seems to rise when I fast. Why does this happen? Another reader has fasting glucose around 144 mg/dL despite an HbA1c of 5.6%.





Quick Answer


Your liver releases glucose overnight and during fasting so the body has energy. Early-morning hormones can increase this release, producing the dawn phenomenon. Morning glucose may also rise because overnight insulin or medicine coverage is insufficient, dinner was late or carbohydrate-heavy, sleep was poor, or illness or steroids are affecting glucose. Fasting readings of 144–157 mg/dL are in the diabetes range if confirmed by laboratory testing, even when HbA1c is 5.6%.




Answer by Dr. Albana Greca, MD, MMedSc



Hi Mary,



A rise from 112 at bedtime to 157 in the morning does not mean that fasting itself is harmful. Even when you do not eat, the liver releases stored glucose to supply the brain and other organs. In people with diabetes or insulin resistance, the body may not produce or use enough insulin to keep this overnight glucose release within range.



The Dawn Phenomenon



In the early morning, hormones such as cortisol and growth hormone signal the liver to release more glucose in preparation for waking. In someone without diabetes, insulin usually balances this rise. With diabetes or insulin resistance, morning glucose can remain elevated. Our guide to why blood sugar rises in the morning explains this pattern in more detail.



Other Reasons Morning Glucose May Be High




  • A large or late dinner, bedtime snack, sugary drink, or alcohol

  • Insulin or diabetes medicine wearing off overnight

  • A missed dose, injection-site problem, or incorrectly stored insulin

  • Poor sleep, sleep apnea, stress, pain, infection, or dehydration

  • Corticosteroid tablets, injections, or other medicines that raise glucose



An overnight low followed by a rebound high is possible in someone using insulin or a sulfonylurea, but it is much less common than the dawn phenomenon or insufficient overnight treatment. Do not assume a nighttime low unless it is documented.



How to Find the Cause



For several nights, record glucose at bedtime, during the night if your clinician recommends it, and immediately after waking before eating or drinking calories. Also record dinner, snacks, medicines, exercise, sleep, illness, and symptoms. A continuous glucose monitor can show the full overnight trend.



A structured blood sugar log can help your clinician distinguish a steady overnight rise from a late meal effect, medication wearing off, or a true low.



What Does Fasting Glucose of 144–157 Mean?



If you have not been diagnosed with diabetes, a laboratory fasting plasma glucose of 126 mg/dL or higher is within the diabetes range. Fasting means at least eight hours without calories. Home meter readings are useful for identifying a pattern but cannot establish the diagnosis by themselves.



Arrange a laboratory fasting glucose and HbA1c. If results are abnormal but you do not have classic symptoms, diagnosis usually requires a second abnormal laboratory result. Our guide to blood tests for diabetes explains the confirmation process.



Can HbA1c Be Normal When Fasting Glucose Is High?



Yes. HbA1c reflects average glucose over roughly the previous two to three months, while a fasting test measures one moment. A person may have isolated morning highs that have not raised the overall average very much. Laboratory variation and conditions affecting red blood cells can also create disagreement between the tests.



An HbA1c of 5.6% is below the prediabetes threshold, but it does not cancel repeated fasting readings in the diabetes range. The discordant results should be repeated and reviewed rather than deciding that the fasting readings are harmless.



What Can Help?



Review dinner portions, late snacks, sugary drinks, sleep, activity, and medicines. A short walk after dinner may help some people when exercise is medically safe. Do not eliminate all carbohydrates, add herbs, begin bedtime medicine, or increase insulin without reviewing the overnight pattern with a clinician.



Do not automatically eat a bedtime snack. It may worsen morning glucose unless it is needed to prevent a documented medication-related low. Compare your readings with the ranges in our guide to normal fasting blood sugar.




Important Safety Note


Contact a clinician promptly if fasting glucose repeatedly remains at or above 126 mg/dL or if you develop excessive thirst, frequent urination, blurred vision, recurrent infections, or unexplained weight loss. Seek urgent care for persistent readings around 300 mg/dL or higher with illness or dehydration, and emergency care for vomiting, abdominal pain, difficult breathing, confusion, fainting, high ketones, glucose above 400 mg/dL, or a meter displaying “HI.”





Doctor’s Note


The safest solution depends on what happens between bedtime and waking. Collect several nights of consistent readings or CGM data before changing treatment. If you are not diagnosed with diabetes, repeated fasting results of 144–157 mg/dL deserve prompt laboratory confirmation even when HbA1c is 5.6%.





Educational safety note: This answer is for general diabetes education only. It does not replace personal medical advice, diagnosis, or treatment. Do not start, stop, or change insulin, tablets, supplements, diet, or exercise plans without speaking with your healthcare provider.




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Last reviewed: July 2026.




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