Why glucose falls at night in type 1 diabetes
With type 1 diabetes, overnight glucose drops do not always have the same cause. There may be too much basal insulin at those hours. A drop may instead relate to an evening correction, an active bolus or greater insulin sensitivity at night. If glucose falls at roughly the same time on several nights in a row, this is an important clue to review in the charts.
Why glucose may fall at night
- Too much basal insulin — recurring overnight drops without new food or extra corrections may suggest excess background insulin at those hours.
- A strong evening correction — if a correction was given before bed, an overnight drop may be a continuation of its effect.
- A dinner bolus is still active — a bolus may continue working overnight, particularly after a late dinner.
- Greater insulin sensitivity at night — for some people, the same amount of insulin has a stronger effect at night than during the day.
- Recurrence at the same time — drops beginning at similar hours on several nights in a row are an important pattern to review.
How to avoid jumping to conclusions
- Do not draw conclusions from a single night: look at several similar episodes.
- Distinguish a drop after a strong evening correction from one without an obvious cause.
- Check the glucose level at the start of the night and whether insulin was active before bed.
- Identify when glucose starts to fall and whether the timing repeats.
- If you use a pump or AAPS, consider automatic corrections, the basal profile and overnight settings.
What is especially useful to examine in the charts
- The exact time an overnight glucose drop begins.
- Whether the drop recurs at similar times on several nights in a row.
- The glucose level at the start of the night and whether insulin was active before bed.
- How quickly glucose falls and whether carbohydrates are subsequently needed to prevent or address a low.
- Whether there is a link with an evening correction, the basal profile, a late bolus or overnight settings.
What to do next
This review can help identify the more likely explanation: too much basal insulin, a strong evening correction, an active bolus before bed or a recurring overnight pattern. It is better to base changes to settings on several similar observations than on a single difficult night.