Hyponatremia (Low Blood Sodium)

  • Medical Author:
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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Drinking not enough fluids and replacing electrolytes such as sodium can lead to hyponatremia (low blood sodium levels), which can be life-threatening.

Dehydration & Exercise = Hyponatremia (Low Blood Sodium)

Viewer Question: My trainer is always telling me to stay hydrated. How much water should I drink when exercising? What will happen if I drink too much?

Fitness Expert's Response: The National Athletic Trainers' Association recommends the following hydration guidelines for exercise:

  1. Two to three hours pre-exercise: 17 to 20 fluid ounces of water or sports drink.
  2. Ten to 20 minutes pre-exercise: 7 to 10 ounces of water or sports drink.
  3. During exercise: Fluid replacement should approximate sweat and urine losses and at least maintain hydration at less than 2% body weight reduction. This generally requires 7 to 10 ounces of water or sports drink every 10 to 20 minutes.

Hyponatremia facts

  • Hyponatremia refers to a low level of sodium in the blood.
  • Hyponatremia may result from excess fluid in the body relative to a normal amount of sodium, or it may be due to a loss of sodium and body fluid.
  • Symptoms are nonspecific and can include mental changes, headache, nausea and vomiting, tiredness, muscle spasms, and seizures.
  • Severe hyponatremia can lead to coma and can be fatal.
  • Treatment of hyponatremia involves intravenous fluid and electrolyte replacement, medications to manage the symptoms of hyponatremia, as well as any treatments for the underlying cause.

What is hyponatremia (low blood sodium)?

Hyponatremia refers to a lower-than-normal level of sodium in the blood. Sodium is essential for many body functions including the maintenance of fluid balance, regulation of blood pressure, and normal function of the nervous system. Hyponatremia has sometimes been referred to as "water intoxication," especially when it is due to the consumption of excess water, for example during strenuous exercise, without adequate replacement of sodium.

Sodium is the major positively charged ion (cation) in the fluid outside of cells of the body. The chemical notation for sodium is Na. When combined with chloride (Cl), the resulting substance is table salt (NaCl).

The normal blood sodium level is 135 - 145 milliEquivalents/liter (mEq/L), or in international units, 135 - 145 millimoles/liter (mmol/L). Results may vary slightly among different laboratories.

Medically Reviewed by a Doctor on 2/3/2015

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