Dawn Phenomenon

Blood sugar often climbs in the early morning with no food involved. Overnight, cortisol and growth hormone rise, and the liver answers by releasing glucose — the dawn phenomenon. A working pancreas covers it with a little extra insulin before you are awake; with type 1 diabetes nothing does, so the rise shows up on the meter.¹

This simulator starts at waking, with the rise already under way. You decide what to do about it: breakfast, a rapid-acting bolus, and — on a pump — a basal rate change set before you wake.

Boluses here model rapid-acting insulin — aspart, lispro, or glulisine.² If you use Regular or another mealtime insulin, the concept holds but the curve shifts later and runs longer; the Bolus Insulin Types simulator compares them side by side.

Pay attention to:

The chart runs from 3 AM to noon, with waking at 6 AM; the shaded hours before it are sleep. The dash-dot-dot curve is the dawn effect: the liver’s glucose release, drawn as a rate that peaks about 45 minutes after waking and fades by about 90 minutes, leaving blood sugar roughly 35 mg/dL higher than it woke. The size varies from person to person, but the pattern is common to most people with diabetes, and it repeats most mornings.³

A breakfast bolus calculated from the carb count covers the carbs, and only the carbs. The dawn rise is extra glucose with no carbs attached, so it is left standing: blood sugar settles higher than it woke. That is why many people find their morning ratio needs to be stronger than the rest of the day’s, or take a small correction on waking before any food.

A pump can raise the basal rate for the hours before waking, but the insulin from a rate change does not arrive when the rate changes. Each tiny dose absorbs on its own curve, so a higher rate set at 4 AM is only beginning to work by 5 and peaking around 6 — which is the point. Set at waking, the same increase lands after the liver has finished. The Insulin Pump Basal simulator shows that lag on its own.

With long-acting basal there is nothing to adjust hour by hour. The tools are the timing and size of the rapid-acting dose — a bolus on waking rather than at the table, or one a little larger than the meal alone needs — and what breakfast is made of. The simulator’s bolus goes to 150% of the meal dose so you can see what a correction on top looks like.