sodium

and Eva Rudolf-Müller, doctor

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

More about the experts All content is checked by medical journalists.

Sodium is one of the electrolytes. Most of it is ingested and excreted in the urine through the kidneys. Here you can read everything you need to know about the importance of sodium in the body, which normal values ​​apply and which diseases affect the sodium level.

What is sodium

Sodium (chemically: Na) is a cation, i.e. a positively charged ion. In total, the body contains around 100 grams of sodium (equivalent to 3150 mmol). It is mainly ingested through food: Since sodium is added to many foods for preservation, especially in industrialized countries, humans consume around 10 to 12 grams a day. This corresponds to about twice the actual daily requirement.

About 50 percent of the total sodium lies outside of the body's cells in the so-called extracellular space. Another 40 to 45 percent are stored in bone tissue. Only 5 to 10 percent are found inside the cell.

The balance between the sodium concentration inside and outside a cell is extremely important for the volume regulation of the cell. The so-called sodium-potassium-ATPase is responsible for its maintenance. This is an ion pump in the cell membrane that exchanges sodium and potassium ions in opposite directions across the cell envelope.

How does sodium excretion work?

Sodium is mainly excreted via the kidneys with the urine, and to a lesser extent via stool and sweat. Our bodies are very sensitive to fluctuations in sodium levels. He compensates for deviations from the normal level (provided he is healthy) with increased or decreased sodium excretion via the kidneys. Various hormones play a role:

The hormone aldosterone, which is released by the adrenal gland when there is a lack of sodium in the blood, reduces the excretion of sodium. The peptide hormone ANP from the heart muscle cells, on the other hand, promotes the excretion of sodium.

When is the sodium determined?

The doctor determines the sodium in the blood or urine in:

• Disorders of the fluid balance and the acid-base balance
• Electrolyte imbalances
• "Water retention" of any kind (edema), for example in the legs or lungs
• High blood pressure (hypertension)
• various hormonal diseases (for example hyperaldosteronism)
• Kidney failure (renal failure)
• increased thirst (polydipsia) or frequent urination (polyuria)

Sodium levels are also monitored in patients in the intensive care unit and during infusion therapy.

The sodium content of sweat is mainly determined when there is suspicion of cystic fibrosis (cystic fibrosis). The doctor gives pilocarpine, a substance that stimulates the sweat glands. The sweat is then collected for half an hour in order to then measure the sodium and chloride concentration in the sample.

Which sodium levels are normal?

	Sodium normal value
blood	135 - 145 mmol / l
24-hour urine collection	50-200 mmol / 24 h
Sweat	5 - 55 mmol / l

When is the sodium low?

If the sodium level is too low, the doctor speaks of hyponatremia. By definition, it exists from a serum concentration of less than 135 mmol / l. The cause is either increased excretion or “thinning” of the blood, i.e. a relative lack of sodium.

An increased excretion of sodium can occur, for example:

• Cerebral hemorrhages, brain tumors and inflammatory brain diseases
• hormone-producing tumors (for example, lung cancer, pancreatic cancer, and prostate cancer)
• severe inflammatory disease of the lungs
• Hormonal disorders such as an underactive thyroid or adrenal fatigue
• Taking certain medications (such as morphine, ibuprofen, tricyclic antidepressants, diuretics)
• Addison's disease

Frequent vomiting, diarrhea or very profuse sweating can also lead to sodium loss.

Dilution hyponatremia is caused, among other things, by chronic kidney or heart failure, liver cirrhosis, protein loss through the kidneys or drinking distilled water.

Further information: Sodium deficiency

If you would like to learn more about the consequences and treatment of low sodium levels in the blood, read the article Sodium Deficiency.

When is the sodium increased?

Excess sodium is known as hypernatremia. It is often caused by water loss - for example, with watery diarrhea, severe fever and sweating or extensive burns. Another possible cause of excess sodium is the increased supply of the cation, for example through:

• Administration of large amounts of sodium-containing solution for infusion (such as sodium chloride or sodium bicarbonate)
• Drinking salt water
• high-sodium dialysate fluid in kidney patients

Hormonal disorders also promote the accumulation of sodium: In primary hyperaldosteronism (also called Conn syndrome), the body produces more aldosterone. This is the hormone that slows down the excretion of sodium.

What happens when you have too much sodium in your body?

If the sodium level in the blood is increased, this first manifests itself in a strong feeling of thirst, weakness, fever and restlessness.

Since people with a reduced perception of thirst (e.g. elderly patients) are unaware of the onset of hypernatremia, they run the risk of developing a severe excess of sodium. The same applies to patients who cannot drink independently, i.e. people in need of care, unconscious or infants.

If the hypernatremia is not compensated for by water intake, the muscle reflexes become over-excited and muscle spasms, as well as clouding of consciousness and even coma.

What to do if the sodium level has changed?

Therapy for hypo- or hypernatremia is based on both the symptoms and the underlying disease.

How is Sodium Deficiency Treated?

If there is hyponatremia due to excessive fluid volume in the body, the patient must limit the amount of fluid they drink. Sodium infusions are given for sudden, severe hyponatremia.

In addition, if possible, the cause will be eliminated or treated. For example, triggering drugs can be temporarily discontinued or the dose reduced.

How is excess sodium treated?

If the excess sodium is due to water loss, the body needs fluids: The doctor can, for example, give a sodium-free infusion with a sugar-containing solution.

If, on the other hand, there is real hypernatremia - i.e. a real excess of sodium ions - the supply of sodium-containing solutions or foods must be restricted. The doctor will also give a drug to increase the excretion of sodium by the kidneys.

Foods high and low in sodium

Knowledge of the salt content of foods is important for patients with conditions that require a low-sodium diet. The following table provides some examples of foods with high or low levels of sodium.

Low sodium content	High sodium content
Coffee, tea and juices	Mineral water rich in sodium
Pasta	Cheese (like feta or parmesan)
Rice, semolina and corn	Sausages, salted meat
fresh fruits and vegetables	Canned fish (such as sardines or rollmops)
Nuts (if not salted)	Ready-made soups and sauces (but there are also low-sodium alternatives)

In general, it is advisable to avoid ready-made products such as ready-made soups or ready-made spice mixtures with a low-sodium diet. As a rule, a lot of sodium is added to these.

Who Should Eat Low Sodium?

Patients may benefit from a low sodium diet in the following cases:

• high blood pressure
• Heart failure
• Chronic renal insufficiency or renal failure
• Liver cirrhosis, liver insufficiency with "water retention"
• "Water retention" (edema) of any kind
• Nephrotic syndrome (loss of protein through the kidneys)
• Secondary hyperaldosteronism
• chronic therapy with steroids or water tablets (diuretics)
• after kidney transplant

The attending physician will tell each patient how much the daily sodium intake should be restricted. On a sodium-reduced diet, you should generally not consume more than 2.4 grams of sodium per day, and on a strictly low-sodium diet even less than 0.4 grams per day.

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