A normal blood sodium level falls between 135 and 145 milliequivalents per liter (mEq/L). This range, measured through a simple blood draw, reflects how well your body is balancing fluid and electrolytes. Sodium below 135 mEq/L is considered low (hyponatremia), while anything above 145 mEq/L is considered high (hypernatremia).
What Sodium Does in Your Body
Sodium is one of the most important electrolytes in your blood. It controls how much water your cells hold onto, keeps your nerves firing properly, and helps your muscles contract. Even small shifts outside the 135 to 145 range can affect how you feel, because your brain is particularly sensitive to changes in sodium concentration.
Your kidneys are the primary regulators. They constantly adjust how much sodium gets excreted in urine and how much water gets retained. Two hormones drive this process: aldosterone, which controls sodium excretion directly, and a group of stress-related hormones called glucocorticoids, which influence metabolism and water conservation. These hormones follow natural rhythms throughout the day, fine-tuning your sodium balance in real time. When you eat more salt, your kidneys respond by releasing the excess sodium in more concentrated urine, actually conserving water in the process rather than flushing it out as you might expect.
When Sodium Drops Too Low
Hyponatremia, or low sodium, is the more common imbalance. It’s classified by severity:
- Mild: 130 to 134 mEq/L
- Moderate: 125 to 129 mEq/L
- Severe: below 125 mEq/L
Mild cases often produce no obvious symptoms, or you might just feel slightly off. As levels drop further, the signs become harder to ignore: headaches, nausea, fatigue, confusion, irritability, and muscle cramps or weakness. Loss of appetite is common. In severe cases, low sodium can cause seizures, hallucinations, loss of consciousness, and can be life-threatening if untreated.
The most common triggers include drinking excessive amounts of water (which dilutes your sodium), certain medications like diuretics that increase fluid loss, and chronic conditions affecting the kidneys, liver, or heart. Intense prolonged exercise combined with drinking only plain water is another well-known cause, especially in endurance athletes. Older adults are at higher risk because the kidneys become less efficient at regulating sodium with age, and many medications prescribed for chronic conditions can affect sodium balance.
When Sodium Climbs Too High
Hypernatremia is defined as a sodium level above 145 mEq/L. Severe hypernatremia is generally considered to start somewhere above 152 to 160 mEq/L, though there’s no single agreed-upon cutoff. High sodium is less common than low sodium in otherwise healthy people, because thirst usually kicks in and prompts you to drink enough fluid to bring levels back down.
The most frequent cause is simply not drinking enough water, which is why hypernatremia occurs most often in people who can’t easily access fluids on their own: very young children, older adults with cognitive decline, or hospitalized patients. Excessive sweating, diarrhea, or vomiting without adequate fluid replacement can also push levels up. Symptoms mirror some of those seen with low sodium, including confusion, irritability, and muscle twitching, but extreme thirst is typically the earliest and most distinctive sign.
How Sodium Levels Are Tested
Sodium is measured through a standard blood test, usually as part of a basic metabolic panel (BMP) or a comprehensive metabolic panel (CMP). A small blood sample is drawn from a vein in your arm, and results typically come back the same day. Whether you need to fast beforehand depends on your provider’s instructions and what other tests are being run at the same time, so it’s worth asking when you schedule the draw.
Your doctor may order a sodium test as part of a routine checkup, or specifically if you’re showing symptoms of an imbalance, taking medications that affect fluid balance, or managing a condition like kidney disease or heart failure. A urine sodium test is sometimes ordered alongside the blood test to help pinpoint whether the issue is related to how much sodium you’re taking in versus how much your kidneys are excreting.
How Diet Affects Your Sodium Balance
The World Health Organization recommends adults consume less than 2,000 mg of sodium per day, which is equivalent to just under a teaspoon of table salt. Most people consume well above that, largely from processed and restaurant foods rather than the salt shaker at the table. Bread, cured meats, cheese, canned soups, and condiments are some of the biggest contributors.
That said, dietary sodium and blood sodium levels aren’t as directly connected as you might assume. Your kidneys are remarkably good at compensating for day-to-day swings in salt intake. Chronically high sodium intake creates problems not by spiking your blood sodium level (your kidneys prevent that), but by forcing your body to retain more water to keep the concentration stable. This extra fluid volume is what raises blood pressure over time. So while your blood test might read a perfectly normal 140 mEq/L, a high-salt diet can still quietly stress your cardiovascular system.