What is the Dawn Phenomenon?

Everyone experiences the Dawn Phenomenon, but not everyone can adjust to this daily morning transition.

high blood sugar reading

You’ve probably not heard of this term unless you have diabetes or know and care for someone who does. It relates to a condition of the glucose-insulin balance we all experience upon awakening which is guided by transitions in circadian rhythms.


When a person finds they are insulin resistant or diabetic, they learn quickly that they must try to achieve a perfect balance of insulin and glucose in their blood at all times.

However, our circadian rhythms have a different plan: in the morning, our bodies are primed to tolerate more glucose after a night’s rest, but at night, we become less tolerant to spikes in blood sugar.

Significant rises in blood sugar at the end of the night comprise what is known as the Dawn Phenomenon. A diabetic person might go to bed with their blood sugar in check, only to wake up to find their numbers skyrocketing in the morning.

Everyone has a dawn phenomenon. However, while nondiabetic people will also experience a rise in glucose in the morning as part of their circadian rhythm, their bodies naturally respond to this rise with the automatic release of more insulin to rebalance their blood sugar. For people with diabetes, this can be a significant challenge to wake up to, as they are incapable of generating insulin in response to these glucose spikes.


In all human beings, the liver generates glucose from its stores of starch and fatty acids. Other organs also produce smaller amounts. These organs normally act on dips in blood glucose at night as we sleep by generating enough to achieve glucose-insulin balance.

As the body’s circadian rhythms shift to signal awakening, stress hormones are released into the bloodstream to help achieve wakefulness. This surge of new hormones increases insulin resistance, which signals for the liver to make even more glucose to maintain a balance so we have enough energy to get out of bed.

People who do not have diabetes are able to generate rises in insulin levels to handle the extra glucose burdening the bloodstream. However, people with diabetes no longer have the ability to do this on their own, and must use insulin.

Dawn phenomenon can be dangerous for some diabetics, who may not see a relief in their glucose levels for hours after awakening. This is a long time to experience uncontrolled blood sugar and can lead to vascular damage as well as increased risk for stroke, kidney disease, eye problems, diabetic neuropathy, and heart disease.


At night, our bodies are guided by shifts in a number of circadian rhythms that include changes in autonomic nervous system function (which regulates stress), heart rate, and blood pressure regulation. Different kinds of hormones, meant to relax us so we can sleep, predominate. Then, as the morning arrives, new sets of hormones surge into the bloodstream to prepare for awakening.

In fact, it’s these differences in vital signs over the course of the night, and into the morning, that can lead to morning heart attacks for those with heart disease and/or diabetes. Both conditions have a significant impact on the circadian rhythms that directly work with the heart; disrupting the very rhythms designed to protect the heart can lead to damaging consequences.

In addition, rapid-eye movement (REM) sleep occurs more frequently in the second half of the sleep cycle, especially near the end, and during this time, blood pressure can vary widely and heart rate may increase just as changes in blood sugar are also occurring which can affect heart function.

Factor in untreated insomnia, sleep apnea, or any other source of sleep deprivation and you’ve got the perfect recipe for heart-health disaster.

About Tamara Kaye Sellman (621 Articles)

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  1. #ICYMI: Circadian Rhythms and Sleep

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