Before addressing the issue of low blood glucose in the morning, let’s discuss hypoglycemia in general.
Hypoglycemia is a reduction in plasma glucose concentration to a level that may induce symptoms or signs such as altered mental status. This condition typically arises from abnormalities in glucose regulation. The most common causes of hypoglycemia in people with diabetes is injecting a shot of insulin, taking too much long-acting insulin, skipping a meal, infections, exercise, and other drugs or alcohol.
Definition of Hypoglycemia
Low blood sugar is usually defined as a blood glucose level below 70 milligrams per deciliter (mg/dL). Readings below 50 mg/dL are more serious and mean that you may need immediate medical treatment.
How common is hypoglycemia?
A Brazilian study, conducted by Lamounier et al, found that during a 4-week evaluation period, at least one hypoglycemic event occurred in 91.7% of study patients with type 1 diabetes and in 61.8% of those with type 2 diabetes.
This included night time hypoglycemia in 54.0% (Type 1) and 27.4% of Type 2 patients; asymptomatic hypoglycemia in 20.6% and 10.6% of patients, respectively; and severe hypoglycemic events in 20.0% and 10.3% of patients, respectively. 
Hypoglycemic symptoms (while awake) are related to the fight or flight activation and brain dysfunction secondary to decreased levels of glucose. Nervous stimulation of the adrenal glands leads to sweating, racing pulse or heartbeat, tremors, anxiety, and hunger. Reduction in brain glucose availability (neuroglycopenia) can show up as confusion, difficulty in concentration, irritability, hallucinations, physical impairments, and eventually, coma and death.
Drugs such as ethanol (including propranolol plus ethanol), haloperidol, tramadol, pentamidine, quinine, salicylates, cocaine, and sulfonamides ("sulfa drugs") have been associated with hypoglycemia.
Other causes of hypoglycemia include the following, singly or in combination (eg, chronic renal failure and sulfonylurea ingestion):
- Autoimmune hypoglycemia: Insulin antibodies and insulin receptor antibodies
- Hormonal deficiencies: low cortisol, low growth hormone
- Critical illnesses: Cardiac, hepatic, and renal diseases; sepsis with multiorgan failure
- Exercise (in patients with diabetes treated with diabetes medications)
- Renal damage that results in excess glucose excretion in the urine.
- Hypoglycemia of childhood from ketosis
How does Hypoglycemia Happen?
Previous blood sugar levels can influence a person’s response to a particular lower level of blood sugar. However, patients with repeated hypoglycemia can have almost no symptoms (hypoglycemic unawareness) and the threshold at which a patient feels the hypoglycemic symptoms decreases as the number of hypoglycemic episodes increase.
A study by Zhong et al., showed that in patients with type 2 diabetes mellitus, a hemoglobin A1c (HbA1c) level above or below 7.0% increases the risk of a first incidence of hypoglycemia that may require hospitalization.. The investigators found that when the HbA1c level ranges between 4.0% and 6.5%, every 0.5% level increase reduces the risk of hospitalization. For patients with a HbA1c level of 8.0-11.5%, the risk of first hospitalization rises with each 0.5% increase in HbA1c.
A study by Eriksson et al., showed that in patients with type 2 diabetes who are also being treated with another drug, the combination of metformin and sulfonylurea carries a higher risk for severe hypoglycemia, cardiovascular disease, and mortality than does the combination of metformin and dipeptidyl peptidase-4 inhibitor (DPP4i). 
Similar to Eriksson, a study by Gautier et al., found that patients with type 2 diabetes treated with metformin plus sulfonylurea or glinide were more likely to experience hypoglycemia than were those treated with metformin plus DPP4i when initially starting insulin. 
Symptoms of Low Blood Sugar in the Morning
- Shakiness or tremor
- Light headedness
- Dry mouth
- Racing heart
- Blurred vision
Complications Associated with Hypoglycemia
Hypoglycemia is a common complication of therapy for diabetes and mild hypoglycemia occurs in more than half of all patients with diabetes who are in insulin therapy. Unrecognized infection causing hypoglycemia in patients with diabetes may cause recurrent hypoglycemic episodes and accelerate the progression of the infection.
The Bottom Line
Low blood glucose in the morning is most likely due to taking too much long-acting insulin at bedtime, not eating an evening snack, exercising late in the day or at night, alcohol intake, or infections.
Suggestions to Prevent Morning Hypoclycemia
Keep a diary of daily activities and dietary intake of complex carbohydrates and protein. Simple carbohydrates fade away faster after an initial spike in blood sugar. It’s always best to eat protein every time you eat a carbohydrate. Daily exercise is good but do not do it late in the day or evening if that is not your routine. If you see a trend of decreasing blood glucose levels in the morning, it may be a sign that your long-acting insulin dose needs to be cut back if you take a dinner-time dose. It is best to talk to your doctor before making any changes yourself.
To be safe, if you wake up feeling unusually tired, shaky or nauseated, drink a bottle of fruit juice or put a packet of glucose granules in a bottle of water and drink it. The goal is to get 15 grams of carbohydrates in fast. One teaspoon of honey, 3 glucose tablets, ½ or can of non-diet soda will work. After taking in additional calories, wait fifteen minutes before taking more to see how you feel. You don’t want to overshoot the mark.
If you have repetitive episodes, you might want to try a continuous glucose monitor and follow these recommendations:
- Glucose goal before breakfast is 70-130 mg/dL
- Before lunch, dinner or a snack is the same
- Two hours after meals, keep under 180mg/dL
- Bedtime levels should be 90-150 mg/dL
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