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QCan having high or low blood sugar cause a seizure?
DR. ORRIN DEVINSKY RESPONDS:
A Substantial changes in blood sugar—either low blood sugar (hypoglycemia) or high blood sugar (hyperglycemia)—can affect the excitability of nerve cells (neurons), allowing seizures to occur more easily. However, no definitive evidence shows that minor changes in blood sugar (e.g., >50 and <200 mg/dL) outside of the normal range provoke seizures.
Changes in blood sugar occur most frequently in people with diabetes. However, less common causes of hypoglycemia include the use of certain medications, excessive alcohol consumption, some critical illnesses, insulin overproduction, and endocrine deficiencies. Hyperglycemia may also be caused by certain medications (such as beta-blockers), illegal amphetamine drug use, and critical illness.
Sudden lowering of the blood sugar, usually from excess insulin administration (and, rarely, from a tumor in the pancreas), can cause a tonic-clonic seizure in anyone, whether or not they have a history of epilepsy. This kind of seizure (also called a grand mal seizure) involves the entire body, loss of consciousness, and violent muscle contractions. Other symptoms of hypoglycemia include sweating, fatigue, headache, anxiety, nausea, dizziness, alterations in vision, hunger, tremor, and confusion. Oral or intravenous glucose can be used to treat hypoglycemia, depending on the severity of the disorder. People who have diabetes with recurrent hypoglycemia should have their treatment regimen adjusted.
Having two or more seizures as the result of blood-sugar changes is not enough to diagnose someone with epilepsy, because these are considered “provoked” epileptic seizures as opposed to the “unprovoked” seizures associated with epilepsy.
Among people with epilepsy, fasting (which lowers blood sugar) or excess consumption of high glycemic foods has not been clearly shown to increase seizure activity. In fact, fasting induces a state of ketosis—an abnormally high concentration of chemical compounds called ketones, which are produced when fatty acids are broken down for energy—that can actually prevent seizures in many people with epilepsy.
Ultimately, we don't know for sure if blood sugar plays a role in seizure control in people with epilepsy. However, several studies are under way and looking to enroll patients. See clinicaltrials.gov under search words “glucose” and “seizure” for more information.