Nocturnal hypoglycemia (NH) refers to an episode of low blood sugar that occurs while a person is asleep, defined as a glucose level dropping below 70 milligrams per deciliter (mg/dL). This is a common concern, particularly for people who use insulin or certain other glucose-lowering medications. Understanding why blood sugar levels drop unexpectedly during the night is the first step toward regaining control and ensuring restful, uninterrupted sleep.
Identifying Nocturnal Hypoglycemia
Recognizing an overnight low can be difficult since a person is not awake to experience typical warning signs like shakiness or dizziness. Instead, the signs manifest through indirect symptoms that disturb sleep or are noticed upon waking. During the event, the body’s stress response can trigger physical reactions, such as drenching night sweats that leave pajamas or bedding damp. Low glucose can also affect brain function, leading to vivid, disturbing nightmares, restlessness, or even crying out during sleep.
The aftermath of a nocturnal episode often provides evidence that a drop occurred. A person may wake up with an unexplained headache, a residual effect of the brain being deprived of its main fuel source. Extreme fatigue, confusion, or unusual irritability in the morning can also signal a low-glucose event occurred while sleeping. In some cases, the body’s natural counter-regulatory hormones cause a “rebound” high blood sugar reading upon waking, which can obscure the underlying low.
Confirmation of nocturnal hypoglycemia relies on monitoring, either by checking blood sugar immediately upon waking or, more effectively, by reviewing stored data. Continuous Glucose Monitors (CGMs) provide a detailed graph of overnight glucose trends, making it simple to spot a drop that occurred hours earlier. Without a CGM, healthcare providers may recommend checking blood sugar between 2:00 a.m. and 3:00 a.m. for several nights to establish a pattern.
Primary Causes of Overnight Blood Sugar Drops
The most frequent cause of an overnight drop relates directly to the timing and action of glucose-lowering medications. Taking too high a dose of basal (long-acting) insulin can create an excess of activity during the overnight hours when the body’s glucose needs are at their lowest. Similarly, certain oral medications, such as sulfonylureas, stimulate the pancreas to release insulin regardless of existing glucose levels, creating a risk if their peak action coincides with the deepest part of the sleep cycle.
Physical activity completed in the evening is another cause, often leading to a delayed drop several hours later. Intense or prolonged exercise depletes the body’s stored glucose (glycogen) from the muscles and liver. The liver then works to replenish these stores, which draws glucose out of the bloodstream overnight, causing levels to fall. This effect can last up to 24 hours post-exercise, making evening activity risky for a nocturnal low.
Alcohol consumption before bed interferes with the body’s ability to maintain stable glucose levels. The liver is typically responsible for gluconeogenesis, the process of creating new glucose and releasing it into the bloodstream to prevent lows. When alcohol is present, the liver prioritizes metabolizing the alcohol, temporarily inhibiting its ability to perform gluconeogenesis. This suppression of the body’s natural defense mechanism can cause blood sugar to plummet hours after the last drink.
An imbalance between carbohydrate intake and medication can trigger an overnight low. If a person miscalculates the carbohydrate content of their evening meal or skips a planned bedtime snack, there may be insufficient circulating glucose to match the activity of basal or mealtime insulin. This mismatch means there is not enough fuel to cover the medication working in the background. This highlights the delicate balance required in managing overnight glucose.
Strategies for Prevention and Safe Management
Preventing nocturnal hypoglycemia involves adjusting the medication regimen with a healthcare provider. They may recommend small reductions in the evening dose of basal insulin or rescheduling the administration time of certain medications to shift their peak activity away from the hours of 2:00 a.m. to 4:00 a.m. Switching to newer, ultra-long-acting insulin analogues can also help, as these medications have a flatter, more consistent action profile with less pronounced peaks.
Strategic eating before bed can provide fuel until morning. If a person’s bedtime glucose level is borderline low or they have had an active evening, a snack containing both carbohydrates and a source of fat or protein is beneficial. The carbohydrate provides immediate glucose, while the fat and protein slow digestion and absorption, offering a sustained glucose release throughout the night. It is also helpful to consistently consume carbohydrates with any evening alcohol to mitigate the liver’s impaired glucose production.
Technology plays a part in prevention, particularly with Continuous Glucose Monitors. Modern CGMs can be set with low-alert features that sound an alarm when blood sugar begins to trend downward or crosses a pre-set threshold. This warning can wake the user, allowing them to treat the low before it becomes severe. Some advanced systems, like automated insulin delivery pumps, can even automatically reduce or suspend basal insulin delivery in response to falling glucose levels.
Once an acute low is detected, the standard of care is the 15-15 rule. This involves consuming 15 grams of fast-acting carbohydrate, such as four ounces of juice, regular soda, or glucose tablets, to rapidly raise the blood sugar. After 15 minutes, the blood sugar level should be rechecked. If the level remains below 70 mg/dL, the 15-gram treatment is repeated until the target range is reached.
Keeping an emergency kit with fast-acting carbohydrates, such as glucose gel or tablets, accessible on the bedside table is important. Once the blood sugar is back in a safe range, consuming a small snack that includes protein and longer-acting carbohydrates, like crackers and peanut butter, can help prevent the blood sugar from dropping again before morning. Having a treatment source nearby ensures a prompt response for safety during a nocturnal event.