Nocturnal hypoglycemia (NH) occurs when blood glucose levels drop below a safe threshold, typically 70 milligrams per deciliter (mg/dL), during sleep. This event is a common, yet potentially dangerous, complication for individuals managing diabetes with glucose-lowering medications like insulin or sulfonylureas. Almost half of all episodes of low blood glucose, and more than half of severe episodes, occur overnight. Preventing these nighttime drops is fundamental for achieving better overall blood sugar control, improving sleep quality, and avoiding serious health risks.
Identifying the Triggers of Nocturnal Hypoglycemia
NH often results from a mismatch between glucose availability and insulin action caused by activities or treatments earlier in the day. Intense physical activity, particularly in the late afternoon or evening, can increase the body’s sensitivity to insulin for up to 48 hours. This effect causes muscles to continue drawing glucose from the bloodstream long after exercise has stopped, increasing the risk of an overnight drop.
Another common factor is the delayed metabolic clearance of alcohol consumed earlier in the evening. The liver normally releases stored glucose (glycogen) to maintain stable blood sugar during sleep. However, when alcohol is present, the liver prioritizes detoxification, inhibiting glucose production (gluconeogenesis). This can lead to significantly reduced blood glucose levels seven to twelve hours later.
Hypoglycemia can also be triggered simply by having an earlier meal than usual or by the delayed absorption of carbohydrates from a high-fat dinner. Additionally, taking certain types of insulin that have their peak effect during the sleep period, such as Neutral Protamine Hagedorn (NPH) insulin, increases vulnerability to nocturnal lows.
Adjusting Evening Diet and Activity Levels
Strategic adjustments to evening lifestyle factors reduce the likelihood of a blood sugar drop during the night. The timing and composition of your evening meal and bedtime snack are important for stabilizing glucose levels. A small bedtime snack containing complex carbohydrates and a source of protein or fat sustains glucose release throughout the night.
Complex carbohydrates, like whole-grain crackers or a small piece of fruit with peanut butter, are digested slowly, providing a steady supply of glucose. This slow release helps to counteract the effects of basal insulin or other medications that peak during the night. Consuming this snack approximately 30 minutes before sleep helps ensure the glucose is entering the bloodstream when it is most needed.
If you engage in intense or prolonged exercise in the late afternoon, you should monitor your blood glucose closely before bed and consider a larger, more substantial carbohydrate intake afterward. Evening alcohol consumption requires extra vigilance because the liver’s glucose-releasing function is impaired for several hours. If you drink alcohol, you must consume it with food and check your blood glucose before going to sleep, as the delayed hypoglycemic effect can be dangerous.
Optimizing Insulin and Medication Schedules
Adjusting the timing and dosage of glucose-lowering medications directly prevents nocturnal hypoglycemia. Basal insulin, designed to provide a constant background level, is a common source of overnight lows if the dose is too high. If you are using an insulin pump, reducing the basal rate by 10 to 20 percent during the hours when lows typically occur, usually between midnight and 6:00 a.m., can be effective.
For those on multiple daily injections, shifting the timing or reducing the dose of long-acting insulin may be necessary. Check blood glucose levels between 2:00 a.m. and 3:00 a.m. for several nights to identify nocturnal drops before making any medication change. This pattern management is crucial because some individuals experience morning hyperglycemia due to the Somogyi effect, which is a rebound high blood sugar caused by the body’s counter-regulatory hormone response to an undetected overnight low.
This differs from the dawn phenomenon, where morning high blood sugar is caused by a natural surge of hormones like cortisol and growth hormone, not by a prior low. The treatment for the Somogyi effect is to decrease the evening insulin dose, while the treatment for the dawn phenomenon is to increase or reschedule the dose. Certain oral diabetes medications, such as sulfonylureas, stimulate the pancreas to release more insulin and can also increase the risk of nocturnal hypoglycemia. Any adjustment to insulin or medication schedules must be done in consultation with a healthcare provider, as improper changes can lead to dangerously high blood sugar levels.
Monitoring Technology and Emergency Planning
Continuous Glucose Monitors (CGMs) have transformed the prevention of nocturnal hypoglycemia by providing real-time data and predictive alarms. CGMs measure interstitial fluid glucose levels every few minutes and can be set to issue an alert when glucose is rapidly falling. The “Urgent Low Soon” alert, for example, can warn a user up to twenty minutes in advance of a severe low, allowing time to consume carbohydrates before the event occurs.
For individuals with frequent or severe nocturnal lows, the use of automated insulin delivery (AID) systems, which integrate a CGM and an insulin pump, is a significant preventative measure. These systems use algorithms to temporarily suspend or reduce insulin delivery when a low is predicted, significantly reducing the incidence of overnight hypoglycemia.
Despite the best preventative efforts, emergency planning remains a necessity. You should keep a source of fast-acting glucose, such as glucose tablets, gel, or juice, readily available near the bed. Furthermore, individuals at risk should have an emergency glucagon rescue treatment, either an injection or a nasal spray, stored nearby. This is the definitive treatment for severe hypoglycemia, especially if the person is unable to consume oral carbohydrates or has lost consciousness.