Understanding the dawn phenomenon and its impact on morning blood sugar readings in diabetes

High morning blood sugar levels can be a natural part of the dawn phenomenon, caused by hormonal shifts that may affect people with diabetes differently. Recognising these patterns is crucial for effective management and avoiding unnecessary concern.

It can be unsettling to check blood glucose after an overnight fast and find it higher than expected. Yet, as Mayo Clinic and Cleveland Clinic note, this can happen because of the dawn phenomenon, a natural rise in blood sugar that tends to occur in the early hours of the morning, usually between 4 a.m. and 8 a.m. According to those clinics, the body releases hormones such as cortisol, growth hormone, glucagon and, in some descriptions, epinephrine, which tell the liver to release glucose in preparation for waking.

For people without diabetes, that hormonal shift is usually matched by enough insulin to keep glucose within a normal range. In those with diabetes or insulin resistance, however, the response may not be strong enough, so morning readings can come back higher than expected. Cleveland Clinic says the phenomenon is common in type 1 and type 2 diabetes, and some estimates suggest it affects more than half of people with the condition.

Mayo Clinic adds that late-night carbohydrates, insufficient insulin and medication timing can all make the rise more pronounced. Other medical guides note that a morning spike is not always caused by the dawn phenomenon alone; waning insulin action or, less commonly, the Somogyi effect may also play a role, which is why patterns matter as much as a single reading.

That is why an isolated high value on waking does not necessarily mean something is wrong. But if the pattern repeats, clinicians advise discussing it with a doctor or nutritionist, since the answer may lie in adjusting food choices, medication doses or the timing of treatment rather than in making any drastic change on one’s own.