Hypoglycemia, or low blood sugar, is defined for most people with diabetes as a blood glucose level below 70 milligrams per deciliter (mg/dL). When this drop occurs during sleep, it is known as nocturnal hypoglycemia (NH). This nighttime event is a significant concern because individuals are often unaware of the symptoms, making self-treatment difficult. Studies suggest that almost half of all low blood sugar episodes, and over half of all severe episodes, occur during sleeping hours. This lack of awareness increases the risk of prolonged low blood sugar, which can lead to serious complications, emphasizing the need for proactive prevention.
Understanding the Causes of Nocturnal Hypoglycemia
The primary reason blood sugar drops at night is an imbalance between glucose-lowering medication and available glucose. A common factor is the timing and dose of basal, or background, insulin. This is especially true if the dose is too high or if older types of insulin are used that peak during the night. For instance, certain intermediate-acting insulins can reach peak effectiveness six to eight hours after a dinner-time dose, often coinciding with the middle of the night.
Physical activity performed late in the day can also cause blood sugar levels to drop hours later, sometimes up to 24 hours post-exercise. Exercise increases the body’s sensitivity to insulin, meaning the medication has a greater glucose-lowering effect long after the workout is finished. Alcohol consumption in the evening is another strong contributor to nighttime lows. When the liver metabolizes alcohol, its normal function of releasing stored glucose to maintain stable blood sugar is impaired.
Pre-Sleep Dietary and Lifestyle Prevention
Strategic adjustments to evening meals and activities can significantly reduce the risk of a nighttime low. A key strategy is timing physical activity earlier in the day to lessen the lingering effects of increased insulin sensitivity during sleep. If late-day exercise is unavoidable, a temporary adjustment to insulin or an increase in carbohydrate intake may be necessary, which should be planned with a healthcare provider.
The composition of the evening meal is important for maintaining stable levels overnight. Pairing carbohydrates with protein and healthy fats helps slow down glucose absorption, providing a more sustained release of energy. If blood sugar levels are trending low before bed, a precisely timed bedtime snack may be advised.
Effective bedtime snacks often contain a balance of carbohydrate, protein, and fat. For example, 15 to 30 grams of carbohydrate paired with a protein source, such as crackers with peanut butter or Greek yogurt, is generally recommended. The protein provides a more delayed source of glucose, which can counteract the peak action of basal insulin.
Alcohol consumption should be limited or avoided entirely before sleep. If alcohol is consumed, it should always be done with a meal or a carbohydrate-containing snack to mitigate the liver’s reduced ability to release glucose. Maintaining consistent meal and snack schedules is also important, as skipping dinner or an evening snack increases the risk of a blood sugar drop during the night.
Adjusting Medications and Monitoring Technology
A physician’s review of the medication regimen is a primary step in preventing recurring nighttime lows. For individuals using insulin pens or syringes, the timing and dosage of long-acting insulin may need adjustment, sometimes by reducing the evening dose by 10% or more, depending on the pattern of lows. Those who use an insulin pump can program a reduction in their basal insulin rate for the hours when lows typically occur. This reduction is highly effective in preventing nocturnal hypoglycemia without causing high blood sugar readings in the morning.
Continuous Glucose Monitors (CGMs)
CGMs are a powerful tool for prevention, providing real-time glucose readings every few minutes. This allows the user to see trends and set customized alerts. Setting a low blood sugar alert to a slightly higher level, such as 90 mg/dL, allows the user to wake up and treat the drop before it becomes a full episode. Some advanced systems also feature a “falling fast” alert, notifying the user when glucose is dropping rapidly and providing greater lead time for intervention.
Emergency Preparedness
Emergency preparedness is necessary for additional safety. Fast-acting carbohydrates, such as glucose tablets, juice, or non-diet soda, should be kept readily accessible at the bedside to treat a mild or moderate low. Anyone at risk for severe nocturnal hypoglycemia should have a modern, ready-to-use form of emergency glucagon on hand. Family members and roommates should be instructed on how and when to administer the glucagon, which triggers the liver to release stored glucose if the individual is unable to self-treat.