Overhydration

Overhydration, also called fluid overload or water intoxication, refers to an excess of body water relative to solutes, which dilutes electrolytes in the blood, most notably sodium. The resulting dilutional hyponatremia can alter cell function and, in the brain, cause edema and neurological symptoms if it develops rapidly or is severe.

Causes of overhydration include excessive fluid intake that exceeds the body's ability to excrete water, reduced excretion due to kidney, heart, or liver disease, and certain medications or hormonal disorders. It can occur during endurance events when large amounts of hypotonic fluids are consumed, in psychiatric conditions such as psychogenic polydipsia, with beer potomania, or in postoperative or elderly patients with impaired thirst regulation. In some cases, hyponatremia arises from impaired water excretion even with modest intake, such as with syndrome of inappropriate antidiuretic hormone secretion (SIADH) or certain diuretics.

Symptoms range from mild to life-threatening and depend on the rate of onset and the degree of hyponatremia. Early signs include nausea, headache, and confusion. As sodium levels fall further, lethargy, nausea with vomiting, seizures, coma, and signs of cerebral edema may occur. Fluid overload can also present with peripheral edema and weight gain.

Diagnosis relies on blood tests showing low serum sodium with decreased serum osmolality, and may include urine studies to determine solute and water excretion. Clinicians classify fluid status as hypovolemic, euvolemic, or hypervolemic to guide treatment.

Treatment depends on severity and rate of onset. Mild, asymptomatic cases are managed with fluid restriction. Severe or symptomatic hyponatremia may require careful administration of hypertonic saline in a monitored setting, with gradual correction to avoid osmotic demyelination. Addressing the underlying cause and adjusting medications are essential.

Prevention focuses on avoiding excessive fluid intake, especially in at-risk groups, and adhering to appropriate hydration strategies during sports or medical care.