Normal blood sodium levels fall between 135 and 145 mEq/L (milliequivalents per liter). This is the standard reference range used by most labs, though slight variations exist between facilities. Sodium below 135 is considered low (hyponatremia), and sodium above 145 is considered high (hypernatremia). Both directions can cause problems, but your body is remarkably good at keeping sodium in that narrow window despite wide swings in what you eat and drink.
Why Sodium Levels Matter
Sodium is the main mineral dissolved in the fluid outside your cells, including your blood. It does three critical jobs: it helps transmit nerve signals, triggers muscle contractions (including your heartbeat), and controls how much water your body holds onto. Your cells maintain a careful balance of sodium outside and potassium inside, creating an electrical charge across their membranes that powers everything from thought to movement.
Because sodium is the primary driver of fluid volume in your blood, your body uses it as a lever to regulate blood pressure. When sodium goes up, you retain water. When sodium drops, you lose water. This is why sodium imbalances affect so many systems at once.
What Low Sodium Looks Like
Sodium below 135 mEq/L is hyponatremia, and it’s the more common of the two imbalances. Interestingly, when sodium drops slowly over weeks or months, you may feel nothing at all. Chronic, mildly low sodium can be completely silent. When symptoms do appear, they tend to start with nausea, vomiting, weakness, and headache.
The danger increases sharply when sodium falls below 125 mEq/L, and severe symptoms typically appear below 120. At those levels, rapid water shifts into brain tissue can cause confusion, delirium, seizures, impaired consciousness, and in rare cases, fatal brain swelling. Children are more sensitive: about half develop symptoms when sodium drops below 125, a level many adults would tolerate without obvious problems. Speed matters too. A sodium level that drops over a few hours is far more dangerous than one that drifts down over days.
Common Causes of Low Sodium
Several everyday medications can push sodium down. Water pills (thiazide diuretics), certain antidepressants, and some pain medications all interfere with the hormonal and kidney processes that keep sodium steady. The recreational drug ecstasy has been linked to fatal cases of hyponatremia, partly because it triggers excessive water drinking while impairing the kidneys’ ability to excrete it.
Medical conditions are the other major category. Heart failure, kidney disease, and liver disease can all cause fluid to accumulate in the body, diluting sodium. Hormonal disorders play a role too: underactive adrenal glands (Addison’s disease) and low thyroid hormone both lower sodium. A condition called SIADH causes the body to produce too much of the hormone that tells kidneys to hold onto water, trapping excess fluid and pulling sodium concentrations down.
Simply drinking too much water, especially during prolonged exercise, can also dilute sodium to dangerous levels. This is why marathon runners and endurance athletes are often warned against overhydrating.
What High Sodium Looks Like
Sodium above 145 mEq/L is hypernatremia, and it usually comes down to one thing: not enough water relative to the sodium in your body. Dehydration from illness, limited access to fluids, or impaired thirst sensation (common in older adults) are the typical causes.
Early symptoms are vague: fatigue, lethargy, and general weakness. These are easy to miss or blame on something else. Severe hypernatremia, particularly when sodium climbs above 160 mEq/L or rises quickly, can progress to seizures, coma, and death. In children, signs include irritability, poor feeding, decreased urine output, and constipation.
The Same Range Applies Across Ages
The 135 to 145 mEq/L reference range holds for both children and adults. There is no separate “elderly” or “pediatric” normal range. What does differ is how vulnerable different age groups are to shifts within or outside that range. Older adults are more prone to hypernatremia because their thirst response weakens with age, and they often take medications that affect fluid balance. Young children are more sensitive to drops in sodium and develop symptoms at higher levels than adults do.
Blood Sodium vs. Dietary Sodium
Your blood sodium level and how much salt you eat are related, but they’re not the same measurement. Blood sodium reflects the concentration of sodium dissolved in your blood plasma, controlled by your kidneys and hormones. Dietary sodium is the total amount of sodium you consume each day, measured in milligrams.
The World Health Organization recommends adults consume less than 2,000 mg of sodium per day, which is equivalent to about 5 grams of salt, or just under one teaspoon. For reference, one teaspoon of table salt contains roughly 2,400 mg of sodium. Most people in Western countries consume well above the recommended limit, largely from processed and restaurant foods rather than the salt shaker.
Eating too much sodium doesn’t typically push your blood sodium above 145. Healthy kidneys compensate by excreting the excess. But chronically high sodium intake does force the body to retain extra water to keep concentrations stable, which raises blood volume and, over time, blood pressure. That’s the real health cost of a high-salt diet for most people: not an abnormal lab result, but sustained cardiovascular strain that adds up over years.
What an Abnormal Result Means
If your blood test comes back outside the 135 to 145 range, the number alone doesn’t tell the full story. What matters is how far outside the range you are, how quickly the change happened, and whether you have symptoms. A reading of 133 in someone who feels fine and is on a diuretic is a very different situation from a reading of 120 in someone who is confused and vomiting.
Mildly abnormal sodium levels are common and often resolve once the underlying cause is addressed, whether that’s adjusting a medication, treating an infection, or simply drinking more (or less) fluid. Severely abnormal levels, below 120 or above 160, are medical emergencies that can cause permanent brain damage if not corrected carefully.