Low Sodium Food: Normal Ranges, High and Low Results Explained

Low sodium food usually means food with limited added salt and sodium, often chosen to support heart, kidney, or blood pressure health. In a blood test, normal sodium is typically 135–145 mmol/L; results outside this range may reflect changes in body water balance, medications, or an underlying health condition rather than diet alone.

Low Sodium Food and Sodium Test Results: The Key Difference

Low sodium food is food that contains relatively little sodium, a mineral found naturally in many foods and commonly added as salt during processing, cooking, or at the table. Choosing lower-sodium options can support healthy blood pressure and may be particularly important for people with certain heart, kidney, or liver conditions. However, a low-sodium diet and a low sodium blood test result are not the same thing.

A normal blood sodium level for most adults is approximately 135–145 millimoles per litre (mmol/L). A value below 135 mmol/L is called hyponatremia, and a value above 145 mmol/L is called hypernatremia. Blood sodium reflects the balance between sodium and water in the body, so an abnormal result is often related to fluid balance, illness, hormone regulation, or medicines rather than the amount of salt eaten on one day.

For dietary choices, the term “low sodium” may have a specific food-labelling meaning in some countries. For example, a food labelled “low sodium” in the United States generally contains no more than 140 milligrams of sodium per serving. Reading the nutrition label and comparing similar products can help people make practical lower-sodium choices.

Normal Sodium Ranges: Age, Sex and Clinical Context

Most laboratories use a reference interval close to 135–145 mmol/L for sodium in blood. The exact range can vary slightly according to the laboratory, the testing method, and the patient population. A clinician should interpret the result using the reference range printed on the individual laboratory report.

Unlike some blood tests, sodium reference ranges do not usually differ substantially by sex in adults. Children, newborns, older adults, and people who are pregnant may have different fluid needs and clinical circumstances, but sodium results are still interpreted primarily in relation to hydration, symptoms, medical history, and other laboratory findings.

A mildly abnormal result may not always indicate an emergency or a long-term problem. For example, vomiting, diarrhoea, fever, intense sweating, recent intravenous fluids, or temporary medication effects can influence sodium levels. A deviation becomes more medically meaningful when it is marked, develops quickly, persists on repeat testing, or occurs with neurological symptoms such as confusion, drowsiness, headache, or seizures.

• 135–145 mmol/L: typical adult blood sodium range
• Below 135 mmol/L: low sodium, or hyponatremia
• Above 145 mmol/L: high sodium, or hypernatremia

What Low Sodium in the Blood Can Mean

Hyponatremia occurs when the sodium concentration in the blood is below the laboratory reference range. In many cases, it means that there is too much water relative to sodium in the bloodstream, rather than that the body has simply not consumed enough salt. The severity depends on the sodium level, how quickly it changed, and whether symptoms are present.

Possible causes include prolonged vomiting or diarrhoea, drinking excessive amounts of water, certain diuretic medicines, some antidepressants, hormone disorders, heart failure, liver disease, kidney disease, and a condition called syndrome of inappropriate antidiuretic hormone secretion (SIADH). Hospitalised patients may also develop low sodium because of acute illness, surgery, pain, or changes in fluid treatment.

Symptoms can be absent when sodium falls slowly or only mildly. When symptoms occur, they may include nausea, headache, muscle cramps, fatigue, unsteadiness, difficulty concentrating, or confusion. Rapid or severe hyponatremia can affect the brain and requires urgent medical care. Treatment depends on the cause and may involve adjusting fluids, reviewing medicines, treating an underlying condition, or carefully correcting sodium under medical supervision.

What High Sodium in the Blood Can Mean

Hypernatremia means that blood sodium is above the usual reference range, commonly above 145 mmol/L. It most often happens when the body loses more water than sodium, leading to dehydration. It does not necessarily mean that a person has eaten too much salty food, although high sodium intake can contribute to thirst and fluid imbalance in some situations.

Common contributing factors include inadequate fluid intake, fever, heavy sweating, diarrhoea, vomiting, uncontrolled diabetes, use of certain medicines, or difficulty accessing or recognising the need for fluids. Older adults, infants, and people with impaired mobility, swallowing problems, cognitive changes, or serious illness may be at greater risk because they may not drink enough water.

Possible symptoms include thirst, dry mouth, reduced urination, weakness, irritability, dizziness, or confusion. More serious dehydration can lead to low blood pressure, marked drowsiness, or neurological symptoms. A clinician may repeat the blood test and check kidney function, glucose, urine concentration, medication use, and fluid status to identify the cause and guide safe treatment.

How to Choose Low Sodium Food

Many people consume more sodium than they realise because most dietary sodium comes from packaged, prepared, restaurant, and processed foods rather than from the salt shaker alone. Breads, cheeses, cured meats, canned soups, sauces, snack foods, ready meals, pickles, and fast foods can all be significant sources. Sodium is also present in products that do not taste noticeably salty.

The World Health Organization recommends that adults consume less than 2,000 milligrams of sodium per day, which is equivalent to less than 5 grams of salt. Individual advice may differ, especially for people with heavy sweating, certain medical conditions, or prescribed nutrition plans. A doctor or registered dietitian can provide personalised guidance.

Helpful low sodium food choices include fresh or frozen vegetables without sauce, fresh fruit, plain oats and rice, dried beans prepared without excess salt, unsalted nuts, fresh poultry or fish, and meals cooked at home with herbs, lemon, garlic, spices, and salt-free seasoning blends. When buying packaged foods, checking sodium per serving and serving size is more informative than relying only on front-of-pack claims.

• Choose “no added salt,” “reduced sodium,” or lower-sodium versions when available.
• Rinse canned beans and vegetables to reduce some surface sodium.
• Compare several brands of the same food, as sodium content can vary widely.
• Use flavourings such as herbs, vinegar, citrus, pepper, and spices instead of adding extra salt.

Diagnosis and Treatment of Abnormal Sodium Results

A sodium result is assessed alongside a person’s symptoms, medical history, examination findings, and other tests. These may include blood glucose, kidney function, potassium, blood and urine osmolality, urine sodium, thyroid function, and adrenal hormone testing. A clinician may also ask about fluid intake, recent illness, alcohol use, exercise, dietary changes, and all prescription or non-prescription medicines.

It is important not to try to correct low or high blood sodium without medical advice. Drinking very large volumes of water can worsen some forms of hyponatremia, while abruptly increasing salt intake may be unsuitable or harmful for people with high blood pressure, heart failure, or kidney disease. Likewise, sodium levels should be corrected gradually in many situations to reduce the risk of complications.

Treatment is directed at the cause. It may include managing dehydration, changing a medication, treating vomiting or diarrhoea, addressing hormone or kidney problems, limiting fluids in selected cases, or giving carefully monitored intravenous fluids in hospital. Acibadem International’s multidisciplinary specialists and JCI-accredited hospitals assess sodium disorders and their underlying causes for international patients when specialist care is needed.

When to Seek Medical Care

Anyone with an abnormal sodium result should discuss it with the clinician who ordered the test, particularly if the result is significantly outside the laboratory range, is new, or is accompanied by symptoms. The clinician can determine whether repeat testing, medication review, hydration advice, or further investigation is appropriate.

Urgent medical assessment is needed for confusion, new severe headache, repeated vomiting, fainting, seizures, pronounced drowsiness, severe weakness, difficulty staying awake, or major changes in behaviour. These symptoms can occur with severe disturbances in sodium or fluid balance and should not be managed at home.

People with heart failure, chronic kidney disease, liver disease, adrenal disorders, or a history of low sodium should seek advice promptly if they develop worsening swelling, breathlessness, persistent gastrointestinal illness, reduced urine output, or new neurological symptoms. Regular monitoring may be recommended for those taking diuretics or other medicines that can affect sodium balance.

Frequently asked questions

What is considered a low sodium food?

A low sodium food is generally one that contains limited sodium per serving. In the United States, foods labelled “low sodium” typically contain 140 milligrams of sodium or less per serving. Nutrition labels should still be checked because serving sizes and total portions eaten can vary.

What is the normal sodium level in a blood test?

For most adults, a normal blood sodium level is about 135–145 mmol/L. Laboratories may use slightly different reference intervals, so the range on the test report should be used. The result should also be interpreted with symptoms, hydration status, and other test findings.

Can eating low sodium food cause low blood sodium?

Usually, no. Low blood sodium is more often caused by an imbalance between water and sodium in the body, such as excess water retention, fluid loss, medication effects, or certain medical conditions. A very restrictive diet may contribute in unusual circumstances, but dietary sodium alone is not the usual cause.

What causes high sodium levels in the blood?

High blood sodium most often results from dehydration or not taking in enough fluids to replace water losses. Fever, diarrhoea, vomiting, sweating, high blood sugar, and some medicines can contribute. A doctor may order additional tests to identify the reason and plan treatment safely.

Should a person add more salt if their blood sodium is low?

A person should not increase salt intake specifically to treat a low sodium blood result without medical advice. The right treatment depends on why sodium is low, and additional salt may not address the cause. In some conditions, self-treatment can worsen fluid balance or raise blood pressure.

Who may benefit from reducing dietary sodium?

Most adults can benefit from avoiding excess sodium as part of an overall balanced diet. Lower sodium intake is often particularly advised for people with high blood pressure, heart failure, kidney disease, or fluid retention. Individual recommendations should be discussed with a qualified healthcare professional, especially when a person has a chronic health condition.

References

• World Health Organization
• U.S. Food and Drug Administration
• National Kidney Foundation
• Merck Manual Consumer Version
• Mayo Clinic

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.