Sodium

What Is Sodium?

Sodium is a mineral — an electrolyte, to be precise — that your body absolutely cannot function without. You probably know sodium best as one half of table salt (sodium chloride), but inside your body it plays a far more sophisticated role than just making food taste better.

Sodium is the main electrolyte in the fluid outside your cells. It helps regulate how much water your body holds onto, keeps your blood pressure in the right range, helps nerves send signals, and allows your muscles (including your heart) to contract properly. Your kidneys are the master controllers of sodium balance, constantly adjusting how much sodium to keep and how much to flush out in your urine.

What Does It Measure?

A serum sodium test measures the concentration of sodium dissolved in the liquid part of your blood (the serum). It is one of the most commonly ordered lab tests in medicine and is typically included in basic and comprehensive metabolic panels.

Your doctor uses this number to assess your body's fluid balance and electrolyte status. Because sodium and water are so closely linked, an abnormal sodium level often tells your doctor more about your water balance than about how much salt you are eating. This is an important distinction that surprises many people.

Normal Ranges

| Group | Range | Unit | |---|---|---| | Adults | 136 – 145 mEq/L | mEq/L | | Children | 136 – 145 mEq/L | mEq/L | | Newborns | 133 – 146 mEq/L | mEq/L | | Older adults (65+) | 136 – 145 mEq/L | mEq/L |

The normal range for sodium is remarkably consistent across age groups and sexes. Your body works very hard to keep sodium within this narrow window, and even small deviations can cause noticeable symptoms. A sodium level below 136 mEq/L is called hyponatremia, and a level above 145 mEq/L is called hypernatremia.

What Does a High Level Mean?

Hypernatremia (sodium above 145 mEq/L) almost always means your body has lost too much water relative to sodium, or in rarer cases, has taken in too much sodium. Common causes include:

• Dehydration: The most common cause. Not drinking enough fluids, excessive sweating, or prolonged vomiting and diarrhea can concentrate sodium in the blood.
• Diabetes insipidus: A condition where the kidneys cannot concentrate urine properly, leading to excessive water loss.
• Excessive sodium intake: Rarely, consuming very large amounts of salt or receiving too much IV saline can raise sodium.
• Certain medications: Lithium, demeclocycline, and some diuretics can cause the kidneys to lose too much water.
• Kidney disease: Impaired kidney function can affect sodium and water balance.

Symptoms include intense thirst, dry mouth, restlessness, confusion, muscle twitching, and in severe cases, seizures. Your doctor will typically recommend increased fluid intake or intravenous fluids to bring sodium back to normal gradually.

What Does a Low Level Mean?

Hyponatremia (sodium below 136 mEq/L) is actually the more common electrolyte abnormality seen in hospitals. It usually means the body is holding onto too much water, diluting the sodium. Causes include:

• Excess water intake: Drinking extremely large amounts of water can dilute sodium, sometimes seen in endurance athletes who over-hydrate.
• Heart failure: The body retains fluid, diluting sodium.
• Kidney disease: Damaged kidneys may not excrete water efficiently.
• SIADH: A condition where the body produces too much antidiuretic hormone, caused by medications, lung diseases, or brain injuries.
• Liver cirrhosis: Advanced liver disease causes fluid retention that dilutes sodium.
• Certain medications: Thiazide diuretics, SSRIs, and some anti-seizure medications are common culprits.
• Hypothyroidism and adrenal insufficiency: Both can contribute to low sodium.

Symptoms range from mild (nausea, headache, fatigue, cramps) to severe (confusion, seizures, loss of consciousness). Severely low sodium (below 120 mEq/L) is a medical emergency. Treatment may involve fluid restriction, medication changes, or intravenous sodium solutions.

When Should You Get Tested?

Sodium is tested routinely as part of standard blood panels, but specific reasons to check include:

• Routine health screening (it is part of the basic metabolic panel)
• If you are taking diuretics, blood pressure medications, or antidepressants
• Symptoms like confusion, nausea, headache, or muscle cramps
• After prolonged vomiting, diarrhea, or heavy sweating
• If you have heart failure, kidney disease, or liver disease
• During hospitalization for almost any condition
• Monitoring during intravenous fluid therapy

How to Improve Your Levels

For most people, keeping sodium in the normal range happens naturally. Here are some tips for specific situations:

If sodium is too high (dehydration):

• Drink adequate fluids: Aim for 8–10 glasses of water per day, more if you are active or in hot weather. Do not wait until you are thirsty — by then, you may already be mildly dehydrated.
• Monitor fluid intake during illness: Vomiting and diarrhea can cause rapid dehydration. Use oral rehydration solutions if needed.
• Be mindful of salt intake: While most hypernatremia is about water loss rather than excess salt, keeping sodium intake under 2,300 mg per day (about one teaspoon of salt) is a good general health practice.

If sodium is too low:

• Avoid excessive water intake: There is such a thing as drinking too much water. During prolonged exercise, balance water with electrolyte-containing drinks.
• Review your medications: If you are on a diuretic or antidepressant, talk to your doctor about whether it could be affecting your sodium.
• Eat a balanced diet: Include sodium-containing foods in moderation. If your doctor has not told you to restrict salt, you do not need to eliminate it from your diet.
• Treat underlying conditions: Managing heart failure, liver disease, or thyroid problems can help normalize sodium levels.

Frequently Asked Questions

Q: Does eating salty food raise my blood sodium level?

Usually not significantly. Your kidneys are remarkably good at maintaining sodium balance. When you eat extra salt, healthy kidneys simply excrete the excess in your urine. Abnormal blood sodium levels are almost always caused by problems with water balance or kidney function, not by how much salt you put on your food. That said, a high-salt diet is still linked to high blood pressure, so moderation is wise.

Q: Can drinking too much water be dangerous?

Yes, though it is rare in everyday life. Drinking extremely large amounts of water in a short period can dilute your blood sodium to dangerously low levels, a condition called water intoxication or hyponatremia. This is most commonly seen in endurance athletes (like marathon runners) who drink excessive amounts of plain water without replacing electrolytes. For most people, drinking when thirsty and during meals is sufficient.

Q: Why is my doctor checking sodium if I feel fine?

Sodium is included in the basic metabolic panel (BMP) and comprehensive metabolic panel (CMP), which are among the most commonly ordered blood tests during routine checkups. Even mild sodium abnormalities can be an early clue to underlying conditions like kidney disease, heart problems, or medication side effects, sometimes before you notice any symptoms. It is a simple, inexpensive screening tool that provides a lot of information.

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This content is for educational purposes only and is not medical advice. Always consult your healthcare provider about your lab results.