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Causes
By Mayo Clinic staffHypoglycemia — defined as blood sugar below 70 milligrams per deciliter (mg/dL) or 4 millimoles per liter (mmol/L) — occurs when there's too much insulin and not enough sugar (glucose) in your blood. Hypoglycemia is most common among people who take insulin, but it can also occur if you're taking oral diabetes medications.
Common causes of diabetic hypoglycemia include:
- Taking too much insulin or diabetes medication
- Not eating enough
- Postponing or skipping a meal or snack
- Increasing exercise or physical activity without eating more or adjusting your medications
- Drinking alcohol
Blood sugar regulation
During digestion, your body breaks down carbohydrates from foods — such as bread, rice and pasta — into various sugar molecules. One of these sugar molecules is glucose, a main energy source for your body. Glucose is absorbed directly into your bloodstream after you eat, but it can't enter the cells of most of your tissues without the help of insulin — a hormone secreted by your pancreas.
When the level of glucose in your blood rises, it signals your pancreas to release insulin. The insulin, in turn, unlocks your cells so that glucose can enter and provide the fuel your cells need to function properly. Any extra glucose is stored in your liver and muscles in the form of glycogen. This process lowers the amount of glucose in your bloodstream and prevents it from reaching dangerously high levels. As your blood sugar level returns to normal, so does the secretion of insulin from your pancreas.
For people with diabetes, the effects of insulin on your body are drastically diminished, either because your pancreas doesn't produce enough of it (type 1 diabetes) or because your cells are less responsive to it (type 2 diabetes). As a result, glucose tends to build up in your bloodstream and may reach dangerously high levels (hyperglycemia). Insulin or other drugs are used to lower blood sugar levels.
If you take too much insulin relative to the amount of glucose in your bloodstream, however, it can cause your blood sugar level to drop too low and result in hypoglycemia. Hypoglycemia may also result if, after taking your diabetes medication, you don't eat as much as usual (ingesting less glucose) or you exercise more (using up more glucose) than you normally would. Your doctor usually works with you to find the optimum dosage that fits your regular eating and activity habits to prevent this imbalance from happening.
- Cryer PE. Glucose homeostasis and hypoglycemia. In: Kronenberg HM, et al. Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa.: Elsevier Saunders; 2008. http://www.mdconsult.com/das/book/body/172399185-6/0/1555/204.html?tocnode=54108916&fromURL=204.html#4-u1.0-B978-1-4160-2911-3..50035-2_3179. Accessed Nov. 19, 2009.
- McCulloch DK. Management of hypoglycemia during treatment of diabetes mellitus. http://www.uptodate.com/home/index.html. Accessed Nov. 9, 2009.
- Hypoglycemia (low blood glucose). American Diabetes Association. http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/hypoglycemia-low-blood.html. Accessed Nov. 19, 2009.
- Hypoglycemia. National Institute of Diabetes and Digestive and Kidney Diseases. http://diabetes.niddk.nih.gov/dm/pubs/hypoglycemia/hypoglycemia.pdf. Accessed Nov. 19, 2009.
- A1C. American Diabetes Association. http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/a1c/. Accessed Dec. 2, 2009.
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