What is the most common cause of hyponatremia?

The most common cause of hyponatremia is the use of thiazide and loop diuretics. These medications are often prescribed for conditions such as hypertension and heart failure. They promote sodium and water excretion in the kidneys, which can lead to a dilutional effect on serum sodium levels, ultimately causing hyponatremia.

Diuretics, particularly thiazides, are known for their propensity to cause electrolyte imbalances due to their mechanism of action. They inhibit sodium reabsorption in the distal convoluted tubule, leading to increased loss of sodium in urine. If water intake remains high or is not adequately adjusted based on the diuretic use, it can exacerbate the drop in serum sodium levels. This can result in clinical symptoms of hyponatremia such as nausea, headache, confusion, and in severe cases, seizures or coma.

While excessive water intake can also cause hyponatremia (particularly in cases of psychogenic polydipsia or inappropriate water consumption), it is less common in the general population. Kidney disease and heart failure are indeed associated with hyponatremia but are generally related to a more complex pathophysiology involving fluid retention and inappropriate secretion of antidiuretic