A Normal Sodium Level

A Normal Sodium Level

For most adults, a normal blood sodium level (measured via a standard blood test called a serum sodium test) is typically between 135 and 145 millimoles per litre (mmol/L).

Sodium is an essential electrolyte that acts as a master regulator for your body’s fluid balance. It plays a vital role in maintaining stable blood pressure, supporting the transmission of nerve signals, and ensuring that your muscles can contract properly.

Reference Units

Blood sodium concentrations are almost universally reported in millimoles per litre (mmol/L). However, depending on the laboratory system or international region, you may see the results expressed as milliequivalents per litre (mEq/L).

The mathematical conversion between these two standard units is completely identical:

1 mmol/L = 1 mEq/L

Reference Ranges

While exact laboratory reference ranges can vary slightly depending on the specific analysis equipment and testing protocols used, results generally fall into the following clinical categories:

• Hyponatraemia (Low): Below 135 mmol/L

• Normal (Sufficient): 135–145 mmol/L

• Hypernatraemia (High): Above 145 mmol/L

What the Ranges Mean

Normal (135–145 mmol/L)

This optimal range indicates a healthy, stable balance of sodium and water in your bloodstream. It demonstrates that your kidneys are filtering fluids efficiently and that your body’s nervous and muscular systems have the ideal environment to function smoothly.

Hyponatraemia (Below 135 mmol/L)

This indicates that the concentration of sodium in your blood is abnormally low. It is usually caused by excess water diluting the sodium in your body—such as overhydrating during heavy endurance exercise—or losing vital fluids through severe vomiting, diarrhoea, or the use of specific medications like diuretics (water tablets). Mild cases can lead to headaches or nausea, whereas severe, rapid drops require urgent medical management.

Hypernatraemia (Above 145 mmol/L)

This means there is an excessive amount of sodium relative to water in the blood. It is most frequently triggered by inadequate water intake, heavy sweating, or losing fluids through an illness without replacing them properly. Common symptoms include intense thirst, restlessness, and dry skin, and treatment involves safely and gradually replacing the body’s lost fluids.

Blood Sodium vs. Dietary Salt

It is crucial to distinguish between the sodium level measured in your blood test and the daily salt intake in your diet.

While eating too much salt (sodium chloride) can steadily elevate your blood pressure over time and impact long-term cardiovascular health, it rarely causes your acute blood test results to fluctuate wildly.

Your kidneys, alongside specialized hormones like aldosterone and antidiuretic hormone (ADH), work constantly behind the scenes to keep your blood sodium tightly secured within that 135–145 mmol/L window, regardless of what you ate for dinner.

UK Guidance

According to official NHS Salt Guidelines, adults should consume no more than 6 grams of salt per day (which equals about 2.4 grams of pure sodium), or roughly one level teaspoon.

Crucially, the average person in the UK consumes much more than this, as the vast majority of the salt we eat is already hidden inside processed foods like bread, ready meals, cereals, and sauces, rather than the salt shaken over food at the dining table. Keeping your daily intake within this recommended boundary helps protect your heart and kidneys over time.

US Guidelines

Readers in the United States can refer to the federal guidelines outlined by the CDC and Dietary Guidelines for Americans. These guidelines officially recommend that adults limit their daily sodium intake to less than 2,300 milligrams (mg) per day.

This aligns directly with the target benchmarks suggested by the American Heart Association (AHA) to reduce the national prevalence of hypertension, stroke, and cardiovascular disease.