Glucose at night: how to read your overnight line

The quietest window of the day

During the day, meals, workouts, coffee, meetings and stairs all leave a mark on your glucose line. At night most of that stops. For seven or eight hours you don’t eat and you barely move, so what’s left on the line says a lot about the day you just had and about your body’s own rhythm.

That is why overnight curves are worth reading. Here are the shapes that come up most often. They are common patterns, not diagnoses: what they mean for you is a conversation for your doctor.

The flat line

A line that stays fairly level through the night is the simplest shape. Glucose leaving the blood and glucose arriving from the liver are roughly balanced, with small waves rather than big swings.

The slow drift down

A line that slopes gently downwards for hours often follows an active day. After a long or hard workout, muscles keep pulling glucose from the blood to refill their glycogen stores, and that can carry on well into the night. An afternoon or evening session makes this more likely to show up overnight.

If you see this shape, look at what you did that day. Ando shows the workout and the night on the same timeline, so the link is easy to spot. Our article on glucose during exercise explains the after-effect in more detail.

The early-morning rise

Many overnight lines climb gently from the early hours until breakfast. In the hours before you wake, your body releases hormones such as cortisol and growth hormone that help you get going, and they also prompt the liver to release glucose. This early-morning rise is often called the dawn phenomenon.

It tends to start somewhere between 3 and 5 am and to run until you wake up, which is why a reading taken right after waking can be higher than one taken at midnight even though you haven’t eaten.

The late-dinner hump

A meal late in the evening often shows as a rise in the first hours of the night, followed by a slow return. Big, rich or late dinners tend to make the hump wider. Comparing nights after early and late dinners is one of the simplest experiments you can run with a CGM, and Ando’s food log lets you note what you ate.

The dip that bounces back

A steep drop in the middle of the night that snaps back when you roll over is often a compression low: you were lying on the sensor, and the pressure made it read lower than your real glucose. We cover it in detail in compression lows explained.

Gaps in the line

Your sensor sends its readings to your phone, and your phone sends them to the sensor maker’s cloud. If your phone is off, out of range or offline for a while, the line can show a gap. Some sensors fill in missed readings once the connection is back; others leave the gap. A gap is a connection issue, not a glucose pattern.

Sleep and glucose

The relationship runs both ways. Researchers have studied for decades how short or broken nights relate to glucose the next day, and a night with big swings can be a restless one. What that means for any one person varies a lot.

Ando doesn’t make claims about your health. It puts both lines on one screen, night after night, so you can see your own pattern: whether your deep sleep looks different on nights with a late dinner, or your line is flatter after rest days.

Your nights in Ando

Every morning Ando shows last night’s glucose next to your sleep from Oura, WHOOP, Garmin, Fitbit or, on iPhone, Apple Health: deep, light and REM sleep, time awake, sleep efficiency and the night’s time in range.

See how it works on the sleep page, or start with Oura, WHOOP or Garmin.

Questions people ask