High sodium levels in the blood, a condition called hypernatremia, are corrected primarily by replacing lost water, either by drinking more fluids or receiving intravenous fluids in a medical setting. Normal blood sodium falls between 135 and 145 mmol/L. Levels above 145 mmol/L are considered elevated, with readings above 158 mmol/L classified as severe. How quickly and aggressively the problem needs to be fixed depends on how high the number is, how fast it rose, and what’s causing it.
Why Sodium Levels Rise
Your body keeps sodium in balance through two main defenses: a thirst signal that drives you to drink water, and a hormone (often abbreviated ADH) that tells your kidneys to hold onto water instead of releasing it as urine. When both systems work properly, even a salty meal triggers enough thirst and kidney adjustment to keep blood sodium in range. Hypernatremia happens when one or both of these defenses fail, or when water losses simply outpace what you’re taking in.
The most common scenario is straightforward dehydration. Illness with vomiting or diarrhea, heavy sweating, fever, or simply not drinking enough water can all tip the balance. Older adults and young children are especially vulnerable because their thirst response is weaker or they can’t access fluids independently. Certain medications, particularly some that increase urine output, can also push sodium higher by draining water faster than the body replaces it.
A less common but important cause is diabetes insipidus, which comes in two forms. In central diabetes insipidus, the brain doesn’t produce enough ADH, so the kidneys release large volumes of dilute urine regardless of how dehydrated the body becomes. In nephrogenic diabetes insipidus, the kidneys themselves don’t respond to ADH. The central form can be treated with a synthetic version of the missing hormone (desmopressin), which effectively restores the kidney’s ability to concentrate urine. The nephrogenic form is harder to manage because the kidneys resist the hormone entirely, so treatment focuses on reducing urine output through other strategies.
How It Feels as Levels Climb
Mild hypernatremia (sodium under 150 mmol/L) often produces intense thirst, dry mouth, and reduced urine output. You might feel restless or irritable without an obvious reason. As levels climb higher, symptoms shift toward the neurological: confusion, muscle twitching, and difficulty with coordination. Severe cases above 158 mmol/L can cause seizures, loss of consciousness, and in extreme situations, permanent brain injury. The brain is particularly sensitive because as sodium rises in the blood, water gets pulled out of brain cells, causing them to shrink.
If you or someone you’re with shows signs of confusion, extreme lethargy, or seizures alongside known risk factors like prolonged illness or inability to drink, that’s an emergency.
Medical Correction in a Hospital
When hypernatremia requires hospital treatment, the primary approach is giving fluids intravenously to slowly dilute the excess sodium. The two most commonly used IV solutions are half-strength saline (0.45% sodium chloride) and a dextrose-water solution. Both are classified as hypotonic, meaning they contain less sodium than blood, so they effectively deliver “free water” that dilutes the concentrated blood. Which solution is chosen depends on whether you also need some calorie support or have other conditions that influence fluid management.
The critical detail is speed. Correcting sodium too fast is dangerous in its own right. When sodium drops rapidly, water rushes back into brain cells and causes them to swell, potentially leading to cerebral edema. For chronic hypernatremia (meaning it developed over more than a day or two), the safe correction rate is no faster than 0.5 mmol/L per hour, with a maximum drop of 10 to 12 mmol/L over a full 24-hour period. If the hypernatremia developed within just a few hours, faster correction is generally safer because the brain hasn’t yet adapted to the higher concentration.
Doctors calculate how much free water your body needs using a formula based on your weight, current sodium level, and target sodium level. This calculation tends to underestimate the true need because it doesn’t account for ongoing water losses from fever, breathing, or continued urine output. So the target gets adjusted repeatedly with frequent blood draws to check progress.
Mild Cases You Can Manage at Home
If your sodium is only mildly elevated and your doctor has confirmed you don’t need IV treatment, the fix is usually simple: drink more water. Plain water is the most effective choice because it contains no sodium. Sports drinks and oral rehydration solutions contain electrolytes including sodium, which can work against you when sodium is already high. Your goal is to replace the water your body is missing so your kidneys can restore balance naturally.
Aim for steady intake spread throughout the day rather than gulping large amounts at once. If you’ve been sick with diarrhea or vomiting, small frequent sips are easier to keep down. Foods with high water content, like watermelon, cucumber, oranges, and soups made with low-sodium broth, also contribute to your fluid intake. Avoid alcohol and large amounts of caffeine while correcting, since both increase urine output.
Reducing Sodium in Your Diet
Once your levels are back to normal, preventing a recurrence often means looking at how much sodium you eat. The World Health Organization recommends under 2,000 mg of sodium per day for adults, which is just under a teaspoon of table salt. Most people consume roughly double that amount, and the majority of it doesn’t come from the salt shaker.
The biggest sources of hidden sodium, according to the CDC, include foods most people eat daily: sandwiches, rice and pasta dishes, pizza, soups, cold cuts and cured meats, breads and tortillas, chips and crackers, condiments, and even desserts. A single deli sandwich can easily contain over 1,000 mg. Canned soups routinely hit 700 to 900 mg per serving, and most cans contain two servings.
Practical steps that make a real difference include reading nutrition labels for sodium per serving, choosing “no salt added” versions of canned vegetables and broth, rinsing canned beans before cooking, and seasoning with herbs, citrus, or vinegar instead of salt. When eating out, asking for sauces and dressings on the side gives you control over the biggest sodium contributors in restaurant meals. These changes matter most for people who’ve had repeated episodes of elevated sodium or who have kidney conditions that make regulation harder.
Treating the Underlying Cause
Replacing water fixes the immediate number, but if the underlying cause isn’t addressed, sodium will climb again. For people with central diabetes insipidus, taking desmopressin consistently keeps the kidneys conserving water the way they should. For those whose hypernatremia stems from a medication, adjusting the dose or switching to an alternative often resolves the problem. Kidney disease, uncontrolled diabetes with high blood sugar (which triggers osmotic diuresis and heavy fluid loss), and hormonal disorders each require their own targeted management.
For older adults living alone or people with cognitive impairment, the fix is sometimes environmental: keeping water within arm’s reach at all times, setting reminders to drink, and having caregivers monitor fluid intake. The thirst mechanism weakens with age, so relying on “drink when you’re thirsty” isn’t always sufficient after about age 65. Establishing a routine of drinking a glass of water at set intervals throughout the day provides a more reliable safeguard than waiting for thirst to kick in.