What are the causes of chronic hyponatremia (low sodium levels) in patients with hypertension (high blood pressure)?

From the Guidelines

Chronic hyponatremia in hypertensive patients is most commonly caused by thiazide diuretics, which can lead to sodium loss through increased urinary excretion, as well as other medications and underlying conditions such as heart failure, kidney disease, or liver cirrhosis. The causes of chronic hyponatremia in patients with hypertension can be multifactorial, including:

• Medications: Thiazide diuretics like hydrochlorothiazide and chlorthalidone, often prescribed at doses of 12.5-50mg daily for hypertension, can cause sodium loss through increased urinary excretion 1. Other antihypertensive medications such as ACE inhibitors (like lisinopril, enalapril) and ARBs (such as losartan, valsartan) can contribute to hyponatremia by affecting kidney function and sodium handling.
• Underlying conditions: Hypertensive patients may have underlying conditions like heart failure, kidney disease, or liver cirrhosis that independently cause sodium imbalances 1.
• Poor dietary habits: Excessive water intake combined with low sodium consumption can exacerbate hyponatremia, and a low-sodium diet (<2400 mg/d) is recommended to prevent hypertension and lower blood pressure in adults with hypertension 1.
• Age-related changes: Kidney function and hormonal regulation changes with age can increase the risk of hyponatremia in elderly hypertensive patients. Management typically involves medication adjustment, addressing underlying causes, and sometimes sodium supplementation or fluid restriction depending on severity and symptoms. Regular electrolyte monitoring is essential for hypertensive patients on diuretics or multiple antihypertensive medications. The most effective approach to managing hyponatremia is to address the underlying cause, and in some cases, sodium supplementation or fluid restriction may be necessary.

From the Research

Causes of Chronic Hyponatremia in Patients with Hypertension

• Chronic hyponatremia can be caused by various factors, including water retention, certain medications, and underlying medical conditions 2.
• In patients with hypertension, diuretics such as thiazides can contribute to the development of hyponatremia, particularly if used in high doses or in combination with other medications 3, 4.
• The use of diuretics, especially thiazide diuretics, can lead to hypokalemia (low potassium levels), which can further exacerbate hyponatremia 5.
• Other factors that may contribute to chronic hyponatremia in patients with hypertension include:
  • Heart failure, which can lead to fluid overload and hyponatremia 2.
  • Syndrome of inappropriate antidiuresis (SIAD), which can cause excessive water retention and hyponatremia 2.
  • Renal impairment, which can affect the kidneys' ability to regulate electrolyte balance and lead to hyponatremia 4.

Mechanisms and Consequences

• The mechanisms underlying chronic hyponatremia in patients with hypertension are complex and multifactorial, involving alterations in fluid balance, electrolyte regulation, and renal function 2, 4.
• Chronic hyponatremia can have significant consequences, including cognitive impairment, gait disturbances, and increased risk of falls and fractures 2.
• Rapid correction of chronic hyponatremia can lead to osmotic demyelination syndrome (ODS), a rare but potentially life-threatening condition 2, 5.