Low sodium levels, a condition doctors call hyponatremia, happen when the amount of sodium in your blood falls below the normal range. Sodium is an essential electrolyte that helps your nerves and muscles work properly and keeps your blood pressure stable. When levels drop too low, water moves into your cells and causes them to swell, which can be dangerous—especially in the brain. The most common causes include excessive fluid intake, certain medications, chronic medical conditions, and severe dehydration from vomiting or diarrhea.
What Is a Normal Sodium Level and When Is It Low?
A normal blood sodium level ranges from 135 to 145 milliequivalents per liter (mEq/L). A diagnosis of hyponatremia is made when sodium falls below 135 mEq/L. Levels below 125 mEq/L are considered severe and require urgent medical attention.
Mild hyponatremia often causes no symptoms at all. Many people discover it during routine blood work. As levels drop further, symptoms can include headache, nausea, confusion, fatigue, and muscle cramps. Severe cases can lead to seizures, coma, and even death.
The speed of the drop matters as much as the final number. A slow decline over weeks may produce few symptoms even at very low levels. A rapid drop over hours can be life-threatening at levels that might otherwise seem moderate.
What Causes Sodium Levels To Be Low?
Hyponatremia is fundamentally a problem of water balance, not just sodium loss. The most common cause is drinking too much water relative to your body’s sodium stores. This dilutes the sodium in your blood and is known as dilutional hyponatremia.
This happens most often in endurance athletes who drink large amounts of water without replacing electrolytes. It also occurs in people who consume excessive water as part of a health or cleansing regimen. In rare cases, psychogenic polydipsia—a condition where someone compulsively drinks large volumes of water—can cause dangerously low sodium.
Hormonal factors also play a major role. The hormone antidiuretic hormone (ADH), also called vasopressin, tells your kidneys how much water to hold onto. When ADH levels are inappropriately high, your kidneys retain water even when your body doesn’t need it. This condition, called syndrome of inappropriate antidiuretic hormone secretion (SIADH), is a common cause of hyponatremia in hospitalized patients.
Medical Conditions That Cause Low Sodium
Several chronic conditions directly affect sodium balance. Kidney disease reduces the kidneys’ ability to filter and excrete water normally. Heart failure and liver cirrhosis cause fluid to accumulate in the body, which dilutes blood sodium. These conditions also trigger hormonal changes that promote water retention.
Adrenal insufficiency, including Addison’s disease, affects the hormones that help the kidneys retain sodium. When these hormones are deficient, the body loses too much sodium through urine. Thyroid disease, particularly severe hypothyroidism, can also lower sodium levels, though this is less common.
SIADH deserves special attention because it has many triggers. Lung diseases like pneumonia and certain cancers can produce ADH-like substances. Brain injuries, strokes, and infections can disrupt the normal regulation of ADH. Some medications, including certain antidepressants and pain relievers, can also cause SIADH as a side effect.
Medications That Can Lower Sodium Levels
A wide range of prescription drugs can cause or worsen hyponatremia. Thiazide diuretics, commonly prescribed for high blood pressure, are among the most frequent culprits. These medications increase urine output but also cause the body to lose sodium in the process.
Other medications that can lower sodium include:
- Selective serotonin reuptake inhibitors (SSRIs) used for depression
- Carbamazepine and oxcarbazepine, used for seizures and nerve pain
- Nonsteroidal anti-inflammatory drugs (NSAIDs) when used regularly
- Proton pump inhibitors used for acid reflux
- Certain chemotherapy agents
- MDMA (ecstasy), which is known to cause dangerous sodium drops
Older adults are especially vulnerable to medication-induced hyponatremia. Their kidneys become less efficient at conserving sodium, and they are more likely to take multiple medications that affect water balance.
Sodium Loss From the Body
Not all low sodium comes from dilution. Sometimes the body genuinely loses too much sodium. Severe vomiting and diarrhea deplete both sodium and water, but if you replace the lost fluids with plain water, your sodium concentration drops.
Excessive sweating from intense exercise or hot weather causes significant sodium loss. People who work outdoors in heat or exercise for hours without electrolyte replacement are at higher risk. This is why sports drinks contain sodium—not just for taste but for maintaining blood electrolyte balance.
Burns that cover a large portion of the body can also cause severe sodium loss through damaged skin. Certain kidney conditions, especially those that cause salt-wasting, can produce chronic low sodium levels.
Who Is Most at Risk for Low Sodium?
Certain groups face a higher risk of developing hyponatremia. Older adults are particularly vulnerable due to age-related changes in kidney function and hormone regulation. They also tend to take more medications that affect sodium balance.
Hospitalized patients frequently develop low sodium. Intravenous fluids, medications, and underlying illness all contribute. One study found that hyponatremia occurs in up to 20 percent of hospitalized patients, though the exact percentage varies by patient population.
Athletes who participate in endurance events, such as marathons or triathlons, face a significant risk. Drinking large volumes of water during prolonged exercise without adequate sodium intake is a well-documented cause of exercise-associated hyponatremia.
People following very low-sodium diets for heart health can also develop low sodium, especially if they also take diuretics. The combination of restricted salt intake and increased sodium loss through medication can push levels below normal.
How Is Low Sodium Treated?
Treatment depends on the cause, the severity, and how quickly the sodium level dropped. For mild cases with no symptoms, simply reducing fluid intake may be enough. Your doctor may also adjust medications that are contributing to the problem.
For more severe cases, treatment may involve intravenous saline solutions. The rate of correction is critical. Raising sodium too quickly can cause a serious condition called osmotic demyelination syndrome, which can lead to permanent brain damage. Doctors typically correct sodium slowly, often no more than 8 to 10 mEq/L in a 24-hour period for chronic cases.
When an underlying condition like heart failure or kidney disease is causing the problem, treating that condition is essential. In cases of SIADH, medications that block the effect of ADH may be used. Fluid restriction is often the first-line treatment for SIADH.
No one should attempt to self-treat low sodium at home. The condition can be dangerous, and improper treatment can cause harm. If you suspect your sodium is low, seek medical evaluation.
When to Seek Emergency Care
Low sodium can become a medical emergency quickly. Seek immediate medical attention if you experience confusion, seizures, severe headache, vomiting, or loss of consciousness, especially if you have been drinking large amounts of water or are taking medications known to affect sodium levels.
These symptoms suggest that brain swelling may be occurring. Brain cells are particularly sensitive to changes in sodium concentration. When sodium drops rapidly, water enters brain cells and causes them to swell, increasing pressure inside the skull. This can be fatal without prompt treatment.
Even without severe symptoms, persistent low sodium deserves medical evaluation. Chronic mild hyponatremia has been linked to falls, fractures, and cognitive impairment in older adults. Identifying and addressing the underlying cause is important for long-term health.
Frequently Asked Questions
Can drinking too much water cause low sodium?
Yes, drinking excessive water dilutes the sodium in your blood and is one of the most common causes of hyponatremia. This is especially dangerous during endurance exercise when you replace sweat losses with plain water only.
What are the first signs of low sodium?
Early signs include headache, nausea, fatigue, and muscle cramps. As sodium drops further, symptoms progress to confusion, seizures, and loss of consciousness.
How quickly can sodium levels become dangerously low?
Sodium can drop to dangerous levels within hours if you consume large volumes of water without electrolytes. A rapid drop is more dangerous than a gradual one, even if the final number is the same.
Can low sodium be prevented?
For most people, drinking water according to thirst and consuming a normal diet with adequate salt prevents hyponatremia. People taking diuretics or with chronic medical conditions should have their sodium checked regularly by a doctor.
