Lack of Sodium (Hyponatremia): Symptoms, Causes, and Treatments

To function correctly, your body constantly maintains its blood sodium level (natremia). This balance is finely regulated by your kidneys, certain hormones, and thirst, via specialized sensors called osmoreceptors. But sometimes disturbances can cause natremia to rise or fall, with varying consequences depending on the case. In this guide, we focus specifically on low blood sodium. Learn what this implies for your body and health, how to recognize the signs, and when it is essential to consult a doctor.

What is a lack of sodium?

Definition of hyponatremia

Hyponatremia corresponds to a blood sodium level below normal physiological values. It is an electrolyte imbalance that can affect both adults and children (Dąbek et al., 2026).

Normal values and risk thresholds

Your natremia is considered normal when it is between 135 and 145 mmol/L. If it drops below 135 mmol/L, it means you are experiencing hyponatremia. According to a review published in Clinical and Experimental Nephrology, three levels of severity are distinguished based on the extent of the decrease.

Level	Natremia (mmol/L)	Severity
Mild hyponatremia	130 – 134	Discrete symptoms
Moderate hyponatremia	125 – 129	First clinical signs
Severe hyponatremia	< 125	Potential life-threatening risk

What is the role of sodium in the body?

Essential functions of sodium

Sodium (Na+) is the main positive ion in the extracellular fluid, i.e., in the blood and interstitial fluids. This electrolyte regulates fluid balance in the body by controlling water movement between intracellular and extracellular compartments, notably via the sodium-potassium pump present in the membrane of each cell. Water naturally moves towards areas where sodium concentration is highest. This mechanism helps stabilize blood volume and blood pressure. Beyond this role, sodium also participates in the transmission of nerve impulses and muscle contraction.

Sodium and hydration

Sodium promotes water retention: it helps your body absorb ingested water and limits its excretion through urine. During prolonged exertion or in hot weather, sweating leads to significant sodium losses. In these contexts, consuming an electrolyte drink improves rehydration and fluid balance compared to plain water alone. According to the nutritional references set by Anses, the adequate sodium intake for an adult is about 1.5 g per day, with an upper safety limit of 2.3 g per day.

What are the symptoms of a lack of sodium?

The intensity of signs depends on both the natremia level and the speed at which it dropped.

Frequent symptoms

You may experience: * loss of appetite and transient nausea * unexplained chronic fatigue * unusual irritability * mild muscle cramps These non-specific manifestations are the most commonly reported in mild to moderate forms. According to Renneboog et al. (2006), mild chronic hyponatremia, often considered benign, increases the risk of falls and attention disorders in elderly individuals.

Severe symptoms

Severe complications of hyponatremia usually occur when natremia: * drops sharply in less than 48 hours: acute form * falls below 125 mmol/L: severe form In these cases, the person's condition can rapidly worsen due to cerebral edema caused by water entering brain cells. Signs that should alert you urgently: * marked confusion * speech disorder * seizures * respiratory distress * loss of consciousness * coma .

What are the causes of a lack of sodium?

Causes related to hydration

Excessive fluid intake, exceeding your kidney's excretory capacity, is one of the main risk factors. This is the case, for example, for athletes who ingest too much fluid during exercise (Altieri et al., 2026). Patients suffering from potomania, a disorder characterized by compulsive water consumption, may also be affected.

Hyponatremia in endurance athletes

In long-distance runners, triathletes, and ultra-trail practitioners, hyponatremia has a specific name: exercise-associated hyponatremia. It occurs when an athlete drinks more water than their actual fluid losses during a long-duration event, without sufficiently compensating for their sodium losses (Altieri et al., 2026). This phenomenon explains why strategic hydration, combining water and sodium intake adapted to the effort, is recommended for long formats rather than excessive plain water consumption.

Medical causes

Certain diseases, hormonal disorders, or medications can also cause hyponatremia: * heart, kidney, or liver failure * hypothyroidism or adrenal insufficiency * taking diuretics, antidepressants, or antiepileptics * syndrome of inappropriate antidiuretic hormone secretion (SIADH), which is excessive production of vasopressin, the hormone that tells the kidneys to reabsorb water instead of eliminating it In rare cases, unexplained chronic hyponatremia can also be a revealing sign of paraneoplastic SIADH, i.e., linked to the presence of a tumor (especially pulmonary). This is one reason why any persistent hyponatremia warrants a thorough medical evaluation.

How to diagnose a lack of sodium?

Diagnosis is based on a blood ionogram, which measures natremia. In case of confirmed hyponatremia, the doctor will prescribe additional tests: urinary and plasma osmolality, natriuresis, creatinine, urea, blood glucose, and, depending on the signs, hormonal tests (thyroid, cortisol) or a cardiac or hepatic assessment. Treatment depends on the identified cause and the general condition (dehydration, fluid overload, etc.). For a detailed overview of the mechanisms involved, the French Society of Endocrinology offers a reference synthesis for healthcare professionals.

How to correct a lack of sodium?

Dietary measures

According to Spasovski (2024), the management of mild to moderate forms, without severe symptoms, should be based on simple measures: * Maintain adequate salt and protein intake through diet * Adapt fluid intake: avoid drinking excessive amounts of pure water No specific diet or overconsumption, but a normal or adequate intake of solutes.

Medical management

The correction of severe hyponatremia requires hospitalization. It must imperatively be gradual: too rapid a rise in natremia exposes to the risk of osmotic demyelination syndrome, a severe neurological condition. Treatment directly depends on the identified cause: fluid restriction in case of SIADH, adaptation or discontinuation of implicated medications, or infusion of hypertonic saline solution in severe forms, as detailed in the MSD Manual. Caution: Do not attempt to correct a lack of sodium by drinking salt water or taking salt tablets without medical advice. Inappropriate correction can cause irreversible brain damage.

Who is most at risk of sodium deficiency?

Certain profiles are more exposed to a lack of sodium: * elderly people * endurance athletes (marathons, triathlons, ultra-trails) * patients with chronic conditions * people on certain medications (thiazide diuretics, antidepressants, antiepileptics) Note: sodium is not the only electrolyte concerned by this type of imbalance. A lack of potassium can coexist with hyponatremia, especially in elderly people or endurance athletes.

Can a lack of sodium be prevented?

Prevention is possible. Here are some practical principles. * Adapt your water intake to your sports activity: do not drink more than necessary * Incorporate electrolytes during prolonged endurance exercise or in hot weather * Inform your doctor of any ongoing diuretic or antidepressant treatment * Regularly monitor natremia in case of chronic disease (cardiac, renal, hepatic) * Maintain a balanced diet with an adapted salt intake .

When should you consult a doctor for a lack of sodium?

Consult a doctor without delay if you experience unexplained fatigue associated with repeated nausea or headaches. If you observe any of the severe symptoms mentioned above in a relative or patient, call emergency services immediately: their life may be at risk.

SEO FAQ – Frequently Asked Questions

What is a lack of sodium?

A lack of sodium, or hyponatremia, corresponds to a natremia below 135 mmol/L. It most often results from excessive water retention by the body, which dilutes blood sodium.

What causes a lack of sodium?

The most common causes are excessive fluid consumption, certain chronic diseases (cardiac, renal, hepatic), hormonal disorders such as SIADH, or the use of certain medications (diuretics, antidepressants, antiepileptics).

Is a lack of sodium dangerous?

Yes, depending on its severity. Mild hyponatremia can remain asymptomatic. A severe form (< 125 mmol/L) can cause seizures, coma, and, in rare cases, death. Prompt medical attention is essential.

What are the first signs of hyponatremia?

The first signs are often non-specific: fatigue, nausea, headaches, and muscle cramps. These symptoms can progress to confusion or balance disorders if natremia continues to drop.

Can drinking too much water cause a lack of sodium?

Yes. Excessive water consumption, especially during prolonged physical exertion, dilutes blood sodium and can cause exercise-associated hyponatremia. This is one of the most documented causes in long-distance runners.

How to prevent a lack of sodium in elderly people?

It is recommended to maintain a balanced diet with adequate sodium intake, regularly monitor natremia when on diuretic treatment, and report any signs of decreased thirst to the treating physician. Regular medical follow-up remains the most effective preventive measure.

In summary: what you need to remember

* Hyponatremia refers to a blood sodium level below 135 mmol/L. * Its causes are numerous: overhydration, SIADH, heart or kidney failure, certain medications. * Symptoms range from simple fatigue to seizures in severe forms. * Correction must always be gradual and supervised by a doctor. * Prevention relies on adapted hydration, a balanced diet, and regular medical follow-up.

Bibliography

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