Hyponatremia: Early Symptoms, Causes & What to Eat

Introduction

A few years ago, a relative of mine, an older man who was always careful about his health, started feeling “off.” He was tired, a little nauseated, and kept losing his train of thought mid-sentence. The family assumed it was age or a stomach bug. It turned out to be a low sodium level in his blood, brought on by a combination of a new medication and drinking a lot of water because he’d been told to “stay hydrated.”

That story is common. Hyponatremia, the medical term for low sodium in the blood, is the most frequent electrolyte disorder doctors see in hospitals. It can be so mild that no one notices, or serious enough to cause seizures, coma, or death. Its early signs are vague and easy to brush off, which is exactly why it gets missed.

If you searched “what is hyponatremia,” “symptoms of low sodium,” or “what causes low sodium,” this guide is for you. We’ll cover what hyponatremia is, what normal sodium levels look like, the early low sodium symptoms, the main causes, how doctors diagnose and treat it, and what to eat. We’ll also clear up a common confusion: people hear for years that sodium is bad, then learn that too little sodium can be dangerous.

A quick but important note: this article is for education. Low sodium is a medical issue that needs proper testing and supervision. Please don’t try to fix it on your own with salt tablets or salty water.

Introduction
What Is Hyponatremia?
Blood Sodium Levels: What’s Normal?
Is Sodium Bad for You?
Early Symptoms of Low Sodium
Clinical Features of Hyponatremia: Mild to Severe
What Causes Low Sodium Levels?
SIADH Symptoms and Why It Matters
How Low Sodium Is Diagnosed: The Blood Test and the Algorithm
Hyponatremia ICD-10 Code
Treatment: How Doctors Raise Sodium Levels
What to Eat With Low Sodium
How to Increase Sodium Levels Safely
Hyponatremia vs. Hypernatremia
Prevention Tips
When to Seek Emergency Care
FAQ
Final Thoughts

What Is Hyponatremia?

So, what is hyponatremia? It’s a condition in which the concentration of sodium in your blood is lower than normal, generally below 135 milliequivalents per liter (mEq/L).

Sodium is an electrolyte, a mineral that carries an electric charge. In some languages and in chemistry, sodium is called natrium (its symbol, Na, comes from that word). That’s why you may see a lab report or a search for “natrium level” meaning the same thing as sodium level.

Sodium does several jobs:

It helps control how much water is inside and outside your cells.
It supports nerve signals and muscle contractions.
It helps regulate blood pressure and blood volume.

Here’s the key idea that surprises many people: hyponatremia is usually a problem of too much water relative to sodium, not necessarily too little salt in your diet. Your body keeps sodium concentration in a tight range. When there’s too much water in the system, or when the body loses sodium faster than it should, the blood becomes diluted. Water then moves into cells, including brain cells, and they swell. That swelling is what causes the most dangerous symptoms.

Hyponatremia can be described in several ways:

By severity: mild, moderate, or severe (based on sodium level)
By speed: acute (developing in under 48 hours) or chronic (developing over days to weeks)
By body fluid status: low fluid volume, normal volume, or high volume (this matters for finding the cause)

Blood Sodium Levels: What’s Normal?

Most labs consider normal sodium levels to be about 135 to 145 mEq/L (equivalent to 135 to 145 mmol/L). If you’re wondering what the blood sodium levels normal range is, that’s the one to remember, though exact reference ranges vary slightly from lab to lab.

Here’s how doctors typically grade low sodium levels:

Category	Blood sodium (mEq/L)
Normal	135 to 145
Mild hyponatremia	130 to 134
Moderate hyponatremia	125 to 129
Severe (profound) hyponatremia	Below 125
Hypernatremia (high sodium)	Above 145

A few things to keep in mind:

The number isn’t the whole story. A person whose sodium fell fast from 140 to 125 in a day may be much sicker than someone who has lived at 125 for months. The brain adapts to slow changes but not to sudden ones.
Mild hyponatremia isn’t always harmless. Even sodium in the low 130s has been linked to unsteady walking, attention problems, falls, and fractures in older adults.
Sodium levels shift with hydration. That’s why a single result is interpreted alongside your symptoms, medications, and other lab values.

Is Sodium Bad for You?

You’ve probably heard “is sodium bad for you” many times, and the honest answer is: it depends on the amount.

Your body needs sodium to live. Without it, nerves, muscles, and fluid balance fail. But for most people in modern diets, the issue is getting too much sodium, mostly from packaged and restaurant food. Long-term high salt intake is associated with:

High blood pressure
Higher risk of heart disease and stroke
Kidney strain
Fluid retention

Major health organizations generally suggest keeping sodium under about 2,300 mg a day (roughly one teaspoon of table salt) for most adults, and often lower for people with high blood pressure, kidney disease, or heart failure.

So both extremes cause trouble. Eating too much salt over years harms your heart and vessels. Having too little sodium in your blood, which is a different thing from how much salt you eat, can harm your brain and muscles quickly. A person can eat a very salty diet and still develop hyponatremia if they have a hormonal problem, drink too much fluid, or take certain medications. And a person on a low-salt diet may have perfectly normal blood sodium.

That difference between dietary sodium and blood sodium is the most important thing to understand in this whole article.

Early Symptoms of Low Sodium

The early signs of hyponatremia are subtle. Many people feel vaguely unwell, blame it on stress or a virus, and carry on. The most common hyponatremia symptoms at the mild stage include:

Nausea, sometimes with vomiting
Headache
Fatigue or low energy
Loss of appetite
Muscle weakness, cramps, or spasms
Restlessness or irritability
Mild confusion or trouble concentrating
Unsteadiness or trouble with balance

If you’re searching symptoms of low sodium, or the more specific symptoms of low sodium levels in blood, this is the cluster to watch. What makes it tricky is that none of these symptoms is specific. Headache and tiredness have a hundred other explanations.

Clues that low sodium may be behind them:

Symptoms began after starting or changing a medication (especially diuretics or certain antidepressants)
You’ve been drinking large amounts of water, for example during a long race, a hot day, or an intense “detox” or hydration challenge
You’ve had vomiting, diarrhea, or heavy sweating
You have a condition such as heart failure, liver disease, kidney disease, or an underactive thyroid
You’re an older adult, a group at higher risk

If low sodium symptoms get worse, they can become dangerous. That leads us to the clinical picture.

Clinical Features of Hyponatremia: Mild to Severe

Doctors talk about the clinical features of hyponatremia in tiers, based on how much the brain is affected.

Mild to moderate features

Nausea without vomiting
Headache
Confusion or “brain fog”
Fatigue and lethargy
Gait disturbance and falls
Muscle cramps

Severe features

Severe symptoms mean the brain is swelling, and they need emergency treatment:

Repeated vomiting
Severe or worsening headache
Marked confusion, disorientation, or drowsiness
Seizures
Trouble breathing
Coma
In extreme cases, brain herniation and death

Acute versus chronic

Acute hyponatremia (under 48 hours) tends to cause more dramatic symptoms because the brain has no time to adapt. It’s seen in marathon and endurance athletes who overdrink water, and in people who take certain recreational drugs like ecstasy (MDMA) and then drink large amounts of water.

Chronic hyponatremia (over 48 hours) often causes subtler problems, like poor concentration, unsteady walking, and falls, because the brain has partly adjusted. The catch is that chronic cases are riskier to correct too quickly, which we’ll cover in the treatment section.

What Causes Low Sodium Levels?

If you want to know what causes low sodium, or what causes low sodium levels, the list is long, but the causes fall into a few groups.

1. Medications

Medications are one of the most common culprits, especially in older adults. Drugs linked to low sodium include:

Thiazide diuretics (water pills such as hydrochlorothiazide), a leading cause
SSRIs and some other antidepressants
Certain anti-seizure drugs, such as carbamazepine and oxcarbazepine
Some antipsychotics
Certain pain medicines and NSAIDs
Some chemotherapy drugs
Desmopressin (used for excessive urination)

Never stop a prescribed medication on your own. If you suspect a drug is affecting your sodium, talk to your prescriber.

2. Too much water intake

Primary polydipsia means drinking excessive fluid, sometimes linked to psychiatric conditions. Endurance athletes can also develop exercise-associated hyponatremia by drinking far more than they lose in sweat, or by losing sodium in sweat while drinking plain water. The old advice to “drink as much as you can” during exercise has contributed to this. Drinking to thirst is generally safer.

3. Fluid retention conditions

In these conditions the body holds on to water, diluting the blood:

Congestive heart failure
Cirrhosis (advanced liver disease)
Kidney disease, including nephrotic syndrome

Here total body sodium may actually be normal or even high, but water is retained in even greater proportion.

4. Hormonal problems

SIADH (syndrome of inappropriate antidiuretic hormone secretion), covered below
Adrenal insufficiency (low cortisol, such as in Addison’s disease)
Hypothyroidism, especially severe cases

5. Fluid and sodium loss

Prolonged vomiting or diarrhea
Heavy sweating
Burns
Overuse of diuretics
Salt-wasting kidney conditions

If these losses are replaced with plain water rather than electrolytes, sodium can fall.

6. Very low solute intake

Sometimes called “tea and toast” syndrome or, in heavy drinkers, “beer potomania.” When the diet contains very little protein and salt, the kidneys can’t excrete excess water properly, so drinking a lot of fluid can dilute the blood.

7. Other triggers

Severe pain, nausea, and stress (which raise antidiuretic hormone)
Recent surgery
Certain lung conditions and infections
Some cancers, particularly small cell lung cancer
Head injuries and brain conditions

Because there are so many possible causes, doctors don’t guess. They follow a structured process, described in the diagnosis section.

SIADH Symptoms and Why It Matters

SIADH stands for syndrome of inappropriate antidiuretic hormone secretion. It’s one of the most common causes of hyponatremia in people who otherwise appear to have normal fluid volume.

Antidiuretic hormone (ADH, also called vasopressin) tells your kidneys to hold on to water. Normally it’s released when you’re dehydrated. In SIADH, the body makes too much ADH at the wrong time, so the kidneys retain water even when the blood is already too diluted.

SIADH symptoms are essentially the symptoms of low sodium itself, since SIADH is a cause, not a separate set of complaints:

Nausea and vomiting
Headache
Confusion, irritability, or personality changes
Muscle weakness or cramps
Fatigue
In severe cases, seizures or coma

What sets SIADH apart is its pattern on tests: low blood sodium, low blood osmolality (dilute blood), yet urine that is inappropriately concentrated, along with a normal fluid status and normal kidney, adrenal, and thyroid function.

Common triggers of SIADH include:

Lung diseases (pneumonia, tuberculosis) and lung cancer
Brain conditions (stroke, meningitis, head injury, tumors)
Certain drugs (antidepressants, anti-seizure drugs, some chemotherapy)
Pain, nausea, and major surgery
Sometimes, no cause is found

Treating SIADH usually involves treating the trigger and, often, limiting fluid intake. Simply eating more salt frequently isn’t enough on its own, because the underlying problem is water retention.

How Low Sodium Is Diagnosed: The Blood Test and the Algorithm

A low sodium blood test is the starting point. It’s usually part of a basic or comprehensive metabolic panel, a routine test that checks several electrolytes at once. The result is often labeled as “sodium” or “Na.”

But the sodium number alone doesn’t tell you the cause. Doctors then follow what’s commonly called a hyponatremia algorithm, a step-by-step approach to work out why the sodium is low. In simplified form:

Step 1: Confirm true hyponatremia.
Measure serum osmolality. Most hyponatremia is “hypotonic,” meaning the blood is truly dilute. Rarely, sodium looks low because of very high blood sugar or high lipids or proteins, and these cases are handled differently.

Step 2: Check urine osmolality.
If urine is very dilute (low osmolality), the kidneys are excreting water properly, which points to excess water intake, as in primary polydipsia or very low solute intake. If urine is concentrated, ADH is active or the kidneys can’t excrete water, which points to SIADH, heart failure, cirrhosis, or volume depletion.

Step 3: Check urine sodium.

Low urine sodium (often below about 30 mEq/L) suggests the body is holding on to sodium, as with dehydration from vomiting or diarrhea, or fluid overload states like heart failure and cirrhosis.
High urine sodium suggests kidney sodium loss, as with diuretics, adrenal insufficiency, or SIADH.

Step 4: Assess volume status.
The doctor examines whether you seem dehydrated (low volume), swollen with fluid (high volume), or normal (euvolemic). This, combined with urine tests, narrows the list of causes.

Step 5: Look for the specific cause.
This may include checking thyroid function, cortisol, kidney and liver function, a review of all medications, and imaging if a lung or brain cause is suspected.

Additional tests sometimes include serum uric acid, blood glucose, and repeat sodium measurements over time.

This structured approach is why self-diagnosing based on symptoms alone isn’t reliable. Two people with the same sodium of 128 can have completely different problems that need opposite treatments.

Hyponatremia ICD-10 Code

For medical records, insurance, and coding, the hyponatremia ICD-10 code is E87.1, which is listed as “Hypo-osmolality and hyponatremia.”

Related codes you may see nearby include E87.0 for hyperosmolality and hypernatremia, and E22.2 for the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Coding rules change over time and depend on the clinical scenario, so professionals should always confirm the current code set.

Treatment: How Doctors Raise Sodium Levels

Treatment depends on three things: how severe the symptoms are, how fast the sodium dropped, and what’s causing it. There’s no single fix.

Severe symptoms (emergency)

If someone has seizures, deep drowsiness, or coma from hyponatremia, they’re treated in a hospital, often in intensive care, with hypertonic saline (a concentrated salt solution, commonly 3%) given by IV in carefully measured doses to quickly reduce brain swelling.

Moderate and chronic cases

Options doctors may use include:

Treating the cause: stopping or changing an offending medication, treating thyroid or adrenal problems, or managing heart, liver, or kidney disease
Fluid restriction: often the first-line approach for SIADH and other water-retention states
Increasing solute intake: for example, salt tablets, protein, or urea in selected cases
Medications: such as tolvaptan (a vasopressin-receptor blocker) or loop diuretics in specific situations, used with close supervision
Adjusting IV fluids: for dehydration-related cases, isotonic saline may be given

Why speed matters: osmotic demyelination

This is a crucial safety point. If chronic low sodium is corrected too quickly, the brain can lose water too fast and nerve cells can be damaged in a condition called osmotic demyelination syndrome. It can cause severe and sometimes permanent problems with speech, swallowing, movement, and consciousness.

For this reason, guidelines generally limit the rise in blood sodium to a small amount per day (commonly no more than about 8 to 10 mEq/L in 24 hours, with lower limits for people at high risk). This is a main reason hyponatremia should be managed by professionals with frequent blood tests, not at home with salt.

What to Eat With Low Sodium

Now to the part of the title many readers care about most: what to eat.

First, a truth that may surprise you. Food alone rarely fixes hyponatremia. When the cause is fluid retention, SIADH, or a medication, eating more salt won’t correct the problem and can even backfire, especially in people with heart, kidney, or liver disease or high blood pressure. Diet is a supporting tool, chosen with your care team, not a substitute for treatment.

That said, food does play a role in many cases, especially when low intake of salt and protein, or heavy fluid intake, contributes. Depending on your situation and your doctor’s guidance, these foods may help.

Foods that supply sodium

Broths and soups (bone broth, chicken broth, miso soup)
Cheese (cottage cheese, feta, parmesan)
Olives and pickles (brined, fermented)
Canned fish like tuna and sardines
Cured or salted foods in moderation, such as ham or smoked fish
Salted nuts and seeds
Bread, crackers, and salted snacks
Soy sauce, tamari, and salted seasonings used lightly
Tomato and vegetable juices (regular, not low-sodium)

Foods that supply protein and solutes

Adequate protein and other solutes help the kidneys excrete water. This is especially relevant in “tea and toast” or low-intake cases.

Eggs
Chicken, turkey, and lean meat
Fish
Beans, lentils, and tofu
Greek yogurt and milk

Foods that support overall electrolyte balance

Potassium-rich foods (bananas, potatoes, spinach, avocados), unless you’ve been told to limit potassium
Oral rehydration solutions after vomiting or diarrhea, which contain both salt and sugar in balanced amounts

What to be careful with

Excess plain water. Drinking large volumes, especially in a short time, can dilute sodium. Follow any fluid limit your doctor gives you.
Low-solute diets. Living on tea, coffee, beer, and toast for long periods is a recognized cause of low sodium.
Very low-salt diets, unless medically advised for another condition.
Alcohol, especially heavy drinking, which affects hormones and fluid balance.
Sports drinks aren’t a cure-all. Some contain less sodium than people assume, and they add sugar.

Who should not simply “eat more salt”

If you have any of the following, do not raise your salt intake without medical guidance:

Heart failure
High blood pressure
Kidney disease
Cirrhosis or fluid retention
SIADH

For these groups, the treatment may be the opposite: restricting fluids or even limiting sodium while treating the underlying condition.

How to Increase Sodium Levels Safely

If you’re asking how to increase sodium levels or how to raise sodium levels, here’s the safest way to think about it.

1. Get tested first. A low sodium blood test confirms whether your level is actually low and how low. Guessing is risky.

2. Find the cause. Raising sodium without addressing the reason it’s low tends to fail. Fixing the cause is the real “treatment.”

3. Follow a personalized plan. Depending on the cause, your doctor may suggest:

Reducing fluid intake
Reviewing your medications
A modest increase in dietary salt and protein
Salt tablets in specific, supervised situations
Medications like tolvaptan or urea in certain cases
Hospital care for severe or symptomatic cases

4. Don’t overcorrect. Faster isn’t better. Too-rapid correction can cause serious brain injury.

5. Never drink salt water to raise sodium. Drinking concentrated salt water can cause vomiting and dangerous shifts in electrolytes. It’s not a safe home remedy.

6. Monitor. Follow-up blood tests show whether your levels are moving in the right direction.

If your doctor has approved a food-based approach for mild, chronic low sodium, the food list above is a sensible place to start, along with keeping a simple food and fluid log so you can spot patterns.

Hyponatremia vs. Hypernatremia

Since we’ve covered low sodium, it’s worth briefly comparing it to its opposite. Hypernatremia means blood sodium above about 145 mEq/L.

Feature	Hyponatremia	Hypernatremia
Blood sodium	Below 135 mEq/L	Above 145 mEq/L
Basic problem	Too much water relative to sodium	Too little water relative to sodium
Common causes	Diuretics, SIADH, heart failure, overdrinking	Dehydration, poor water access, diabetes insipidus, fever
Typical symptoms	Nausea, headache, confusion, cramps, seizures	Intense thirst, dry mouth, weakness, irritability, confusion, seizures
Main risk	Brain swelling	Brain cell shrinkage
Who is most at risk	Older adults, athletes who overdrink, people on certain drugs	Infants, older adults, hospitalized patients who can’t drink
Typical treatment	Treat cause, limit fluids, sometimes saline	Replace water carefully

Notice that both problems are really about the balance of water and sodium, not sodium alone. Both are usually detected on the same routine blood test, and both need to be corrected gradually.

Prevention Tips

You can’t prevent every case, but some habits lower your risk:

Drink to thirst, not by force. Unless a doctor has told you otherwise, your thirst is a good guide.
During long exercise, avoid overdrinking. Consider fluids that contain sodium, and don’t drink far beyond your sweat losses.
Review medications with your doctor or pharmacist, especially if you take diuretics or antidepressants, and ask whether sodium monitoring is advisable.
Get sodium checked after starting or changing a medication that can affect it, particularly if you’re older.
Replace losses smartly. After vomiting, diarrhea, or heavy sweating, use oral rehydration solutions rather than only plain water.
Eat a balanced diet with adequate protein and salt-containing foods, not just tea, toast, or alcohol.
Manage chronic conditions like heart, liver, kidney, and thyroid disease with regular follow-up.
Be cautious with recreational drugs like ecstasy, and don’t combine them with heavy water drinking.
Follow fluid limits if you’ve been given them, especially with SIADH or heart failure.

When to Seek Emergency Care

Call emergency services or go to the nearest emergency department right away if someone has low sodium symptoms plus any of these:

A seizure
Severe or worsening headache
Repeated vomiting
Marked confusion, extreme drowsiness, or difficulty waking
Trouble breathing
Fainting or loss of consciousness

Also seek urgent care if you’ve been vomiting or drinking a lot of water during or after an endurance event and start to feel confused or very unwell.

For milder but persistent symptoms like ongoing fatigue, nausea, headaches, cramps, or unexplained falls, book a doctor’s appointment and ask for a sodium blood test. It’s a quick and inexpensive check.

FAQ

What is hyponatremia in simple terms?

It’s a condition where the sodium in your blood is too diluted, usually below 135 mEq/L. It’s most often caused by too much water relative to sodium rather than by a lack of salt in your diet.

What are the early symptoms of low sodium?

Nausea, headache, tiredness, muscle cramps, loss of appetite, mild confusion, and unsteadiness. These early hyponatremia symptoms are easy to mistake for other problems.

What are normal sodium levels?

About 135 to 145 mEq/L for most labs. This is the usual blood sodium levels normal range, though labs vary a little.

What causes low sodium levels?

Common causes include diuretics and other medications, SIADH, heart failure, cirrhosis, kidney disease, adrenal or thyroid problems, excessive water intake, vomiting or diarrhea, and very low protein and salt intake.

Is sodium bad for you?

Too much sodium over the long term raises blood pressure and heart disease risk. But your body needs sodium, and too little in the blood is dangerous. It’s about balance.

Can you have low sodium and still eat a salty diet?

Yes. Blood sodium depends on the balance of water and sodium, and on hormones and organ function, not just on how much salt you eat.

How is hyponatremia diagnosed?

With a low sodium blood test, often followed by blood and urine osmolality, urine sodium, a check of fluid status, and other tests, following a stepwise hyponatremia algorithm to find the cause.

How do you raise sodium levels?

By treating the cause, adjusting fluids and medications, and in some cases using salt, protein, or specific drugs. Severe cases need IV hypertonic saline in a hospital. The correction must be gradual and supervised.

Can drinking too much water cause hyponatremia?

Yes. Drinking large amounts of water in a short time, or far beyond what you need, can dilute your blood sodium. This can happen in athletes and in people with certain conditions.

Can low sodium be dangerous?

Yes. Severe or rapidly developing hyponatremia can cause seizures, coma, and death. Even mild chronic cases can lead to falls and fractures, especially in older adults.

What’s the difference between hyponatremia and hypernatremia?

Hyponatremia is low blood sodium (below 135 mEq/L); hypernatremia is high blood sodium (above 145 mEq/L). They’re opposite problems with different causes and treatments.

What is the hyponatremia ICD-10 code?

E87.1, “Hypo-osmolality and hyponatremia.”

Are SIADH symptoms different from hyponatremia symptoms?

Not really. SIADH is a cause of hyponatremia, so its symptoms are those of low sodium: nausea, headache, confusion, weakness, and in severe cases seizures.

Final Thoughts

Hyponatremia is common, often missed, and sometimes serious. The main lessons:

Hyponatremia means blood sodium below 135 mEq/L, and it’s usually about water balance, not just salt intake.
Normal sodium levels are roughly 135 to 145 mEq/L; below that is low, above 145 is hypernatremia.
Early symptoms of low sodium (nausea, headache, fatigue, cramps, mild confusion) are vague, so don’t ignore them, especially with risk factors.
What causes low sodium ranges from medications and overhydration to SIADH and heart, liver, kidney, or hormone problems.
A low sodium blood test plus a stepwise hyponatremia algorithm finds the cause.
How to raise sodium levels safely depends on the cause and must be gradual, because overly rapid correction can damage the brain.
Food helps but rarely fixes things alone. Broths, cheese, olives, eggs, and other protein and salt-containing foods can support treatment when your doctor agrees.
Sodium isn’t simply “bad.” The goal is balance.

If you take away one thing, let it be this: if you feel persistently off and have any risk factors, ask for a simple blood test. Catching low sodium early is far easier, and safer, than treating it once it’s severe.