Hyponatremia (Low Blood
Sodium Level)

Hyponatremia (Low Blood Sodium Level): Overview

Alternative names: Low Blood Sodium Level, Low Sodium, Salt Need, Salt Intake Requirement

Hyponatremia is a lower-than-normal concentration of sodium in the blood.  Sodium is an essential electrolyte in our bodies, vital for proper muscle and nerve function, and stabilizing blood pressure; we cannot live without it.  When drinking lots of water throughout the day, salts (especially sodium) are washed through the kidneys and voided.  A normal blood sodium level is between 135 and 145mEq/L (milliequivalents per liter).  Below that the condition is called hyponatremia; severe hyponatremia occurs at 120mEq/L.

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About 40% of the body's sodium is contained in bone; 2-5% occurs within organs and cells, and the remaining 55-58% is in the blood and the fluid surrounding cells.  The body continually maintains a specific concentration of sodium in the blood and fluids.

When sodium levels are too high or low, the intestines and kidneys respond to adjust concentration back to normal.  For example, when Hyponatremia occurs (the level of sodium in the blood is too low), the intestines increase their efficiency of sodium absorption, and the kidneys reduce the amount they release into urine.

Table salt (chemical formula NaCl) contains both sodium and chloride ions.  One teaspoon (6 grams) of salt contains 2,300mg of sodium.  Consuming too much salt raises blood pressure and therefore the risk of heart disease and stroke.  Major health organizations recommend consuming no more than 1,500 to 2,300mg of salt per day – in other words, we should try to keep intake below 1,500mg per day and certainly not go above 2,300mg.

Incidence; Causes and Development; Contributing Risk Factors

On average, Americans are consuming more than 3,400mg of sodium every day.  Some 70% of this comes from processed foods and restaurants.  The body requires less than 500mg (roughly 14 of a teaspoon) per day to function properly and very few people fall below this requirement.

Sodium levels can fall for two reasons: inadequate intake or the body removing it too quickly.  Hyponatremia can be caused by the following:

  • Abnormal consumption or excretion of dietary sodium or water

    • Long-term maintenance of a low salt diet.  Some people hear "salt is bad for you", reduce salt intake too much, and put their health at risk.
    • Consuming too much water (either by drinking, or intravenously): the water in the bloodstream dilutes the sodium
    • Excessive drinking of beer – which is mainly water and low in sodium – in combination with poor diet.
    • Dehydration
  • Kidney disease or kidney failure, in which the kidneys have difficulty eliminating fluids
  • Liver cirrhosis
  • Heart failure
  • Disorders in organs that control the body's regulation of sodium or water:

    • The adrenal gland secretes a hormone called aldosterone that travels to the kidneys, where it causes them to retain sodium by not excreting it into the urine.  Addison's disease causes hyponatremia as a result of low levels of aldosterone due to damage to the adrenal gland.
    • The hypothalamus and pituitary gland are also involved in sodium regulation by making and releasing vasopressin, known as anti-diuretic hormone, into the bloodstream.  Like aldosterone, vasopressin acts in the kidney, but it causes it to reduce the amount of water released into urine.  With more vasopressin production, the body conserves water, resulting in a lower concentration of plasma sodium.
    • Certain types of cancer cells produce vasopressin, leading to hyponatremia
  • Diuretic drugs used to treat high blood pressure by increasing the excretion of sodium into the urine.  These drugs make the kidneys produce more urine, which can wash away too much sodium.  Usually only mild hyponatremia occurs in patients taking diuretics, but when combined with a low sodium diet or with the excessive drinking of water, severe hyponatremia can develop.
  • Antidepressants
  • Old age.  Elderly patients have a reduced ability to regulate the concentrations of various nutrients in the bloodstream.
  • Severe and prolonged diarrhea, causing the daily output of 8-10 liters of fluid from the large intestines, results in the loss of large amounts of water, sodium, and various nutrients.  Some diarrheal diseases release particularly large quantities of sodium and are therefore most likely to cause hyponatremia.
  • Prolonged vomiting.
  • Excessive loss of sweat (high in sodium and water) during a race on a hot day can prevent the body from maintaining adequate sodium levels.  Marathon runners can sweat 8-10 liters during a race and about 30% experience mild hyponatremia.  Those consuming only water can deplete their sodium levels to the point where they experience neurological disorders and require emergency treatment.
  • Hypothalamus and pituitary disorders.
  • Certain types of cancer.
  • Hypothyroidism
  • Diabetes insipidus
  • Cushing's syndrome

Hyponatremia is more likely to occur in athletes and people living in warmer climates, who require higher water intake and sweat more, putting them at greater risk of losing excess sodium.

Signs and Symptoms

Symptoms of low blood-sodium level (hyponatremia) can be absent, mild, or severe.  The brain is very sensitive to sodium levels and neurological symptoms are thought to result from the movement of water into brain cells, causing them to swell and disrupt their functioning.  Symptoms of moderate hyponatremia include:

  • Confusion / disorientation
  • Difficulty thinking
  • Weakness
  • Muscle cramps/spasms/twitches
  • Headaches
  • Poor balance
  • Nausea
  • Vomiting
  • Irritability
  • Fatigue / tiredness / low energy / lethargy
  • Heart palpitations

Eventually, severe hyponatremia can lead to:

Diagnosis and Tests

Hyponatremia is confirmed by acquiring a blood sample, preparing plasma, and using a sodium-sensitive electrode for measuring the concentration of sodium ions.  Normal blood sodium levels are 136 to 145 milliequivalents per liter (mEq/L) of blood.  A patient with hyponatremia will have a blood sodium level lower than 136 mEq/L. Some doctors use a lower threshold of 135.

The next step is to discover the underlying cause of low plasma sodium levels.  Unless the cause is obvious, a variety of tests are run to determine if sodium was lost via urine, diarrhea, or vomiting.  Other tests determine abnormalities in aldosterone or vasopressin levels.

A basic metabolic panel (blood tests) can ascertain the amounts of electrolytes and minerals in the blood.  A urine test can help determine the cause of low sodium:

  • If blood levels are low but urine levels are high, the body is losing too much sodium
  • Low levels in both blood and urine mean the body is not taking in enough sodium or too much water is being consumed

The patient's diet and use of diuretics must also be considered.

Treatment and Prevention

Treatment will depend on the cause but adjusting levels of water and salt intake should be adequate for preventing any imbalance.  For every two quarts of water consumed per day consider adding 12 teaspoon of salt.

Severe hyponatremia can be treated by infusing a solution of 5% sodium chloride in water into the bloodstream.  Moderate hyponatremia due to use of diuretics or an abnormal increase in vasopressin is often treated by instructions to drink less water each day.  Hyponatremia due to adrenal gland insufficiency is treated with hormone injections.

When hyponatremia is severe, it is considered a medical emergency that is treated in a hospital since very low plasma sodium levels can result in seizures and coma.  The doctor will slowly increase the blood sodium levels with intravenous (IV) fluids.  Additional treatment depends upon the underlying cause of hyponatremia.

If you take diuretics, make sure you have your blood sodium levels checked on a regular basis.  If you are sick and symptoms include vomiting or diarrhea, follow your doctor's recommendations for replacing lost fluids with clear liquids or electrolyte replacement fluids.  People who run marathons and train intensely should drink electrolyte replacement fluids to keep sodium levels balanced.

Prognosis; Complications; Seek medical attention if...

Hyponatremia is just one manifestation of a variety of disorders.  While hyponatremia can easily be corrected, the prognosis for the underlying condition that causes it varies.

Not enough salt can lead to various complications including:

  • Increased cholesterol (LDL) and Triglycerides.  Low sodium diets have been shown to cause an increase of 4.6% in cholesterol 5.9% in triglycerides.  A second study confirmed this with findings of a 2.5% increase in cholesterol and a 7% increase in triglycerides.
  • In another study, only several days on a low sodium diet increased insulin resistance.

Death that occurs during hyponatremia is usually due to other features of the disease rather than to the hyponatremia itself.

It is important to seek medical attention if symptoms of low sodium levels persist.

On This Page

Hyponatremia / Salt Intake Need:

Signs, symptoms & indicators of Hyponatremia (Low Blood Sodium Level):

Symptoms - Food - Preferences

Afternoon coffee/sugar craving

Craving coffee or tea can indicate a need for salt.

Symptoms - General

Symptoms - Muscular

Symptoms - Sleep

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Risk factors for Hyponatremia (Low Blood Sodium Level):

Symptoms - Food - Beverages

Symptoms - Food - Intake


Symptoms - Muscular

Recommendations for Hyponatremia (Low Blood Sodium Level):


Increased Salt Consumption

The concentration of sodium in the blood plasma depends on the total amount of sodium and water in the circulatory system.  Hyponatremia, can be corrected either by increasing sodium or by decreasing water intake.

Reduced Water Consumption

Mild hyponatremia is treated by reducing water intake and monitoring the use of diuretics.

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