Nighttime hypoglycemia is an episode of low blood sugar during the night; these are common and affect nearly every person with type 1 diabetes and a significant minority of those with type 2 diabetes.
How Does Sleep Affect Glucose Production?
To understand nighttime hypoglycemia, it's necessary to know how sleep affects glucose production. Normally the body produces two hormones -- glucagon and epinephrine -- that combat low blood glucose levels. However, glucagon production is typically lower at night. In addition, type 1 diabetes impairs glucagon production, which becomes further depressed with each episode of hypoglycemia.
Other factors, including longer periods between meals and increased insulin sensitivity, also contribute to hypoglycemia during sleep.
What Are the Signs of Nighttime Hypoglycemia?
While the standard signs of early hypoglycemia include sweating, heart racing, shakiness, hunger and anxiety, nighttime hypoglycemia presents an unusual challenge, as the symptoms of this occurring may not be as apparent during sleep.
Keep an eye out for night sweats, poor sleep quality, headache or a tired feeling upon awakening, and higher than normal blood glucose levels in the morning, which is the "rebound" effect in blood sugar levels known as the Somogyi effect.
If a person does not awaken during an episode of nighttime hypoglycemia, low blood sugar remains untreated and may progress to more pronounced hypoglycemia, which is characterized by drowsiness and confusion with symptoms that easily can remain masked during sleep. Nighttime hypoglycemia may not be recognized until blood glucose levels are dangerously low, possibly low enough to cause convulsions or coma.
Avoiding Nighttime Hypoglycemia
To avoid or prevent nighttime hypoglycemia, it is helpful to maintain a consistent late-afternoon and evening routine of diet, activity and insulin dosing.
Special Considerations for Insulin Dosing and Nighttime Hypoglycemia
The timing and dosing of long-acting insulin in the evening is critical to preventing nighttime hypoglycemia. Long-acting insulin is most active between four and eight hours after an injection. When long-acting insulin is administered at the evening meal, the peak insulin response tends to occur during sleeping hours. By changing the timing of a dose of long-acting insulin closer to bedtime, it places hypoglycemic levels closer to the waking hours, when hypoglycemia symptoms are more easily recognized and treated.
It is particularly important to avoid overdosing insulin -- particularly long-acting insulin -- to avoid nighttime hypoglycemia. For example, if an evening blood sugar measurement is high after a large meal, one may be tempted to administer a larger-than-typical dose of short-acting plus long-acting insulin to treat the hyperglycemia. Although this may work well during the day, changes in hormone released at night, with lower levels of glucagon production while sleeping, may yield lower-than-expected blood sugars compared to the insulin dose, resulting in hypoglycemia.
Eating a bedtime snack of complex carbohydrates -- such as dried fruit, granola or oatmeal -- may help prevent nighttime hypoglycemia by maintaining a more steady release of glucose to accompany the action of long-acting insulin.
What Precautions Should Be Taken for Eating and Exercise?
Hypoglycemia can occur if people wait too long between meals or exercise vigorously without eating. Precautions should be taken to eat a snack in between meals when necessary. Also, the timing of exercise and eating is important. Exercise can cause a drop in glycogen stores, which will result in lower blood glucose levels approximately four to eight hours later. Therefore, late-afternoon or evening exercise may contribute to nighttime hypoglycemia. Eating slowly-absorbed carbohydrates -- such as dried fruit, nuts, or granola -- after exercise can help counteract this type of exercise-related hypoglycemia.