It often happens that blood sugar is raised on waking even when we haven’t consumed any food or drink before bedtime. One reason for high fasting blood sugar on waking is the Dawn Phenomenon also known as the dawn effect, which is a natural rise in blood sugar that occurs in the early hours of the morning. At bedtime, even if your blood sugar is in a healthy, normal range it will begin to become elevated around 2-3am and raised on waking.
This natural shift in blood sugar levels happens because of hormonal changes in the body and these physiological processes occur in everyone. The hormones including growth hormone, cortisol, glucagon, and epinephrine are influenced by our circadian rhythm and at our waking time these hormone levels are increased in our blood stream encouraging the liver to release more glucose into the blood. The increased blood sugar triggers the pancreas to release insulin that helps the glucose enter our cells. Even in healthy people the Dawn phenomenon occurs and the resulting surge in energy (glucose) helps us to wake up.
Insulin is thus released in response to the rise in morning blood sugar, however, someone with prediabetes or type 2 diabetes may not be able to control the raised blood sugar because they are insulin resistant and do not secrete enough of the hormone. Healthy people without insulin resistance produce enough insulin to control a morning spike caused by the dawn effect.
Whilst the dawn phenomenon is a natural process that happens to everyone, there are things we can do to soften the effect so we can keep our blood sugar levels in a health range. Hormones such as cortisol are involved in the dawn phenomenon, but it is also known as the stress hormone. Reducing our stress levels and maintaining a balanced circadian rhythm by going to bed early and not using blue-light screens before bed can help. We should also try to limit carbohydrates in dinner to minimize blood sugar before bed and eat a low-GI/low carb breakfast as our blood glucose level is naturally elevated in the morning.