Those with diabetes must always be aware of their blood glucose levels.

This includes being aware of what might happen to your levels while sleeping.


Nighttime hypoglycemia is generally defined as having a blood glucose reading lower than 72 mg/dl. Without treatment, that level could continue to slip; if it reaches 40 mg/dl or below, the person could slip into a coma.

Possible Causes

Suppose you are having a late dinner. You take your insulin bolus beforehand, and have your meal. Later, at bedtime, your glucose count is right where you want it to be, at 121 mg/dl. That means the injection did what it was supposed to do, to cover your meal. However, that bolus you took works for as long as five or six hours. Now it’s 2 am and your sugar is still dropping, even though you’re sleeping.


Or maybe you had some alcohol during the evening. Your liver is busy clearing out the alcohol and a lot less focused on producing glucose. Late night at the gym? A walk after supper? Exercise can temporarily raise glucose levels for hours, leaving you with good bedtime numbers, only to have them fall later in the night.

Symptoms and Solutions

Symptoms of hypoglycemia – shaking, sweating, chills and clamminess, lightheadedness or dizziness, blurred vision – might not be felt by someone who is asleep. Sometimes if hypoglycemia comes on during sleep the patient might cry out or have nightmares, but not always.

Doctors at Joslin Diabetes Center recommend that your blood glucose reading at bedtime should be at least 140 mg/dl. If you are wearing an insulin pump, and you feel you might be at some risk of low overnight readings, then adjust the pump to deliver less basal insulin though the night. You can also consider consuming a healthy snack just before bedtime.

If this is a frequent problem, then the use of a continuous glucose monitor (CGM) might be necessary. This device provides an alarm that alerts when sugar levels are too low or too high.


The common risk with going to bed with high blood glucose is that the patient will be spending roughly one-third of the day with damaging levels of glucose in their bloodstream. Repeated instances of this can lead to the longer term complications of diabetes.

The risk of an emergency situation is not so great but cannot be ignored. Infection, stress, dehydration and myriad other things might continue to drive numbers higher during the night which can result in disabling complications.

The numbers required to achieve that level of risk, however, are generally in excess of 600 mg/dl. If this is near the reading at bedtime, if the patient is elderly or if there is a history of unstable glucose levels, then efforts should be made to lower blood glucose with insulin, prior to going to bed.

Sources: Joslin Diabetes Center and Richard R. Rubin, Ph.D., C.D.E.