Hypoglycemia, or low blood sugar, is defined as a fall in blood glucose levels, typically below 70 milligrams per deciliter (mg/dL). When this energy source drops too low, it can provoke a generalized seizure, characterized by an excessive surge of electrical activity across both sides of the brain. The brain relies almost exclusively on glucose for fuel. This lack of glucose translates directly into uncontrolled electrical discharge because the brain’s complex signaling processes cannot be sustained without a steady energy supply.
The Brain’s Unique Energy Dependency
The human brain accounts for only about two percent of the body’s total weight, yet it consumes approximately 20 percent of the body’s entire glucose-derived energy supply. This high metabolic rate reflects the continuous energy demand required to maintain consciousness and regulate bodily functions. The brain’s reliance on glucose is unique because it possesses only a very limited capacity to store this fuel.
The small amount of glycogen stored in astrocytes provides only a minimal, short-term reserve that is rapidly depleted during a glucose shortage. Furthermore, the blood-brain barrier prevents large molecules, such as fatty acids, from entering the brain. Fatty acids are a common alternative fuel source for other organs, but their use is restricted because they are typically bound to albumin in the blood. Consequently, when glucose levels drop, the brain has no significant internal reserves or immediately available alternative fuels.
The Neurochemical Pathway to Seizure
The central nervous system’s vulnerability to low glucose levels leads to a physiological cascade that promotes seizure activity. The initial failure point is the disruption of adenosine triphosphate (ATP) production, the molecule that powers cellular functions. Neurons require a constant supply of ATP to fuel the sodium-potassium pump (Na+/K+-ATPase), which maintains ion gradients across the cell membrane.
When ATP levels drop due to hypoglycemia, the pump slows or fails, collapsing the normal ion balance. Potassium ions accumulate outside the cell, and sodium ions build up inside, causing the neuron’s resting membrane potential to become unstable. This destabilization lowers the threshold required for a neuron to fire an electrical impulse, making the network hypersensitive.
The glucose shortage also impairs the balance of neurotransmitters, shifting the brain toward an over-excited state. The inhibitory neurotransmitter Gamma-Aminobutyric Acid (GABA) is synthesized from glutamate, a process requiring a continuous supply of glucose. When glucose is depleted, the synthesis and recycling of GABA are significantly reduced, lifting the inhibition on neuronal activity.
This reduction in inhibitory GABA signaling, combined with increased excitatory glutamate activity, creates neuronal hyperexcitability. This uncontrolled excitation overwhelms the brain’s regulatory mechanisms, resulting in the hypersynchronous, excessive electrical discharge characteristic of a generalized seizure.
Recognizing and Addressing Hypoglycemia
Symptoms of Hypoglycemia
The brain provides several warning signals before a seizure, grouped into physical and cognitive symptoms. Physical (adrenergic) symptoms are the body’s initial response, involving the release of stress hormones like adrenaline. These include sweating, shaking, a rapid heart rate, and an intense feeling of hunger.
As glucose levels continue to fall, cognitive (neuroglycopenic) symptoms emerge, reflecting the brain’s direct energy deprivation. These symptoms precede severe consequences like loss of consciousness or seizure. They may involve confusion, difficulty concentrating, slurred speech, blurred vision, and a general feeling of disorientation.
Risk Factors
The most common risk factors for severe hypoglycemia are conditions or treatments that disrupt glucose regulation, primarily in people with diabetes. Individuals using insulin or certain oral diabetes medications are at greater risk if dosage is not matched with food intake or physical activity. Other risk factors include severe alcohol consumption, certain metabolic disorders, or prolonged fasting.
Treatment
Immediate intervention is necessary to prevent a seizure once symptoms appear. Mild to moderate hypoglycemia is typically treated using the “rule of 15s,” which involves consuming 15 grams of fast-acting carbohydrate. Examples include glucose tablets, half a cup of fruit juice, or non-diet soda. After 15 minutes, blood sugar is rechecked, and the 15-gram treatment is repeated if the level remains below 70 mg/dL.
For severe hypoglycemia where the person is unconscious or unable to swallow, immediate medical assistance is required, as oral treatment is unsafe. In this emergency, a glucagon injection or nasal spray is administered. Glucagon is a hormone that signals the liver to release its stored glucose, rapidly raising blood sugar to halt the progression toward a seizure.