Dizziness, which can manifest as lightheadedness, unsteadiness, or a feeling of faintness, is a physiological response to significant fluctuations in blood glucose. Both an excess of sugar (hyperglycemia) and a deficit of sugar (hypoglycemia) can disrupt normal bodily functions enough to trigger a dizzy spell.
How High Blood Sugar Causes Dizziness
Elevated blood sugar levels trigger osmotic diuresis, a process designed to flush excess glucose out of the body, which leads to fluid loss. The high concentration of glucose in the blood enters the kidneys’ filtering units and draws water along with it. This results in frequent and excessive urination, known as polyuria.
The rapid loss of fluid volume through increased urination causes dehydration. This dehydration leads to a measurable decrease in overall blood volume. This reduction in volume can lower blood pressure (hypotension), which affects the circulation of blood to the brain.
When the brain does not receive a steady, adequate blood supply, the result is often lightheadedness or dizziness. This type of dizziness develops slowly, over the course of several hours or even days, as the dehydration progresses. Other accompanying symptoms include extreme thirst and blurred vision due to fluid shifts within the eye.
Why Low Blood Sugar Also Causes Dizziness
Low blood sugar, or hypoglycemia, is defined as a blood glucose level below 70 milligrams per deciliter (mg/dL) for most individuals. The brain relies almost exclusively on glucose for its energy supply, so when levels fall, its function is immediately impaired. This direct impact causes neuroglycopenic symptoms, which include dizziness, confusion, difficulty concentrating, and weakness.
As glucose levels drop further, the body activates a counter-regulatory defense system, releasing hormones like adrenaline (epinephrine) to try and raise blood sugar quickly. This surge of adrenaline causes adrenergic symptoms. These symptoms, which often accompany the dizziness, include rapid heart rate, sweating, shakiness, and intense hunger.
The dizziness from hypoglycemia comes on very suddenly, in sharp contrast to the slow onset associated with high blood sugar. The feeling is often described as acute lightheadedness or a whirling sensation tied to the immediate lack of fuel for the central nervous system. A person experiencing this can feel better rapidly once glucose is consumed and the brain’s energy supply is restored.
Immediate Actions and Medical Consultation
If dizziness occurs and you suspect a blood sugar issue, first check your blood glucose level if a meter is available. If the reading is high (hyperglycemia is over 180 mg/dL), the immediate action is to hydrate with non-sugary fluids like water. This helps dilute the excess glucose in the bloodstream and encourages the kidneys to flush it out, reversing dehydration.
If the blood sugar reading is low (below 70 mg/dL), follow the “15-15 rule” to raise it quickly. Consume 15 grams of a fast-acting carbohydrate, such as four ounces of fruit juice, a tablespoon of honey, or three to four glucose tablets. After waiting 15 minutes, recheck the level and repeat the 15-gram treatment if the level remains below the target.
Any persistent or recurring dizziness related to sugar levels warrants a visit to a healthcare provider for evaluation. Seek immediate medical care if dizziness is accompanied by severe symptoms like fainting, extreme confusion, vomiting, or a fruity odor on the breath. These signs can point to serious conditions, such as diabetic ketoacidosis (DKA) or severe hypoglycemia, which require urgent intervention.