July 21, 2020

What is Sodium?

Sodium is an electrolyte and is found in all bodily fluids. The body must have sodium to function. Electrolytes form ions (electrically charged particles) in body fluids. The ions carry the electrical energy needed for many functions including muscle contraction and the transmission of nerve impulses. Sodium is the major cation in extracellular fluid and helps to regulate things like the amount of water in the body as well as blood pressure.[1]

Why take a Sodium blood test?

A sodium test measures the concentration of sodium in the blood. It may be used alongside the other electrolytes in the body to form an electrolyte panel. Other electrolytes which may be measured include potassium, bicarbonate and chloride, all of which conduct electrical impulses in the body.[2]

A major increase or decrease in sodium can indicate too much (hypernatraemia) or too little (hyponatraemia) sodium in the blood. Dehydration can be a major cause of low sodium levels because sodium can be lost from the body in all fluids i.e. blood, sweat, tears, diarrhoea and vomit.

You can check your level of sodium together with up to 50 biomarkers integral to good health within Forth’s Vitality and Ultimate blood tests.

What function does Sodium have in the body?

Sodium is an essential nutrient required by the body for normal cellular homeostasis. It has a vital role in ensuring the plasma volume of the blood is correct. Sodium can be thought of like a sponge which draws fluid into the extracellular space like plasma volume. The movement of fluid helps to keep the sodium gradients inside and outside of the cell equal.[3]

Sodium also has a role in the transmission of nerve impulses. For example, when a nerve cell isn’t sending signals, it is resting. However, all cell membranes have a protein pump called the sodium-potassium pump which uses energy to pump three sodium ions out of a cell and two potassium ions in to generate action potentials.

For sodium to function in the body, we require between 200 and 500mg of sodium each day. However, the western diet means this amount is often exceeded which can cause various health issues, like blood pressure and cardiovascular disease. [4]

How do changes in Sodium affect health and wellbeing?

Changes in sodium levels can affect our health and wellbeing. High levels of sodium are called hypernatraemia, while low sodium levels are referred to as hyponatraemia.

Hypernatraemia is an electrolyte imbalance where there is a rise in the sodium concentration of the blood. It is characterised by a blood concentration of over 145 mmol/L.[5]

Hyponatraemia is where the body has a sodium deficiency or an abnormally low sodium concentration in the blood. Hyponatraemia is the most common of the electrolyte conditions and often affects females, the elderly and hospitalised patients.[6]

If you are worried about your sodium levels or just want to check where you fall on the range, you can test your sodium level with Forth’s leading blood test service.

What can cause Sodium to change?

Hypernatraemia is often caused by water depletion and the loss is unable to be replaced because water may be unavailable or the person may not be able to get water for themselves or the feeling of thirst is impaired. It is also caused by an increased intake of salt, particularly in the absence of water or through the administration of hypertonic sodium solutions.[7]

A common cause of hyponatraemia is dehydration. Dehydration occurs when the body loses more water than it takes in. Therefore, dehydration depletes both water and electrolytes from the body causing unpleasant symptoms.[8]

There are other causes of hyponatraemia, whereby the body loses water and sodium, including:

  • An underactive adrenal gland
  • Kidney problems
  • The use of diuretics
  • Diarrhoea and vomiting
  • Burns
  • Trauma
  • Pancreatitis

Having excess fluid in the body can also cause hyponatraemia and can also leave the body swollen. Too much water in the body is called fluid overload or hypervolemic hyponatraemia and can be caused by:

  • Liver cirrhosis
  • Cardiac failure
  • Nephrotic syndrome.

What are the most common symptoms?

Hypernatremia is caused by increased water loss and therefore, there is an imbalance between sodium and water in the body. Symptoms include:

  • Dry mouth and eyes
  • Headache
  • Increased thirst
  • Restlessness
  • Feeling agitated
  • Convulsions[9]

The symptoms of hyponatraemia will depend on the severity and how quickly the condition develops. As the condition becomes more severe, symptoms include:

  • Headache
  • Nausea
  • Vomiting
  • Reduced energy levels
  • Confusion
  • Weakness
  • Muscle cramps
  • Changes in personality[6]

How to keep Sodium in the healthy range

Typically, the western diet encourages excess salt intake and so the amount of sodium we ingest greatly exceeds the amount we need. Increased sodium intake can negatively impact our health.[10]

Increased sodium intake is linked to high blood pressure which increases the risk of developing cardiovascular disease. However, reducing sodium intake has the opposite effect and is much better for our health.[11] Research has shown that reducing the amount of salt we eat, lowers the risk of cardiovascular events such as heart attacks and stroke. Adults should eat no more than 6g of salt per day, while the amount of sodium we eat shouldn’t exceed 2.5g. Traffic light label systems on foods make it easier for us to see how much salt or sodium a food contains. [12]

However, you should always read the labels carefully because it may be stating how much is in 100g. So, if what you’re eating is 500g, the food will contain 5 times the amount of salt or sodium.

Dehydration is associated with increased salt intake, too. Therefore, it is always essential to keep yourself hydrated. Sip little and often throughout the day rather than waiting until you feel thirsty. Big gulps of water when you’re thirsty can also disrupt your electrolyte and water balance and have adverse effects. If you are ill, it is important to keep yourself hydrated, too. Vomiting and diarrhoea results in losses of electrolytes and water. Try to sip water and replace lost electrolytes with electrolyte replacement therapy, available from pharmacies and supermarkets.

Exercise is great for our health, but we must remember to replace the water we lose through sweat and urine otherwise we risk becoming dehydrated which can affect our performance. Endurance exercise can cause both water and electrolyte losses, but overdrinking can be harmful, too. It is important to drink before, during and after exercise. If you are taking part in the prolonged exercise you may need to incorporate a drink which contains electrolytes. However, if the exercise is not prolonged or strenuous, this is unnecessary. It is essential that you are aware of your fluid and electrolyte intake during exercise.[13]

- Health scores calculated



[1] Lab Tests Online. (2012). Sodium Test. Available at:

[2] NHS. (2018). Electrolyte Test. Available at:

[3] Luetkemeier, M, J et al. (1997).  Dietary Sodium and Plasma Volume Levels with Exercise. Sports Med: 23(5): pp279-286.

[4] Aburto, N, J., Ziolkovska, A., Hooper, L., Elliot, P., Cappuccio, F, P and Meerpohl, J, J. (2013). Effect of Lower Sodium Intake on Health: Systematic Review and Meta-Analyses. BMJ: 346.

[5] BMJ. (2019). Hypernatraemia. Available at:

[6] You and Your Hormones. (2019).  Hyponatraemia. Available at:

[7] Sterns, R, H. (2019). Etiology and Evaluation of Hypernatraemia in Adults. Available at:

[8] Asim, M et al. (2019). Dehydration and Volume Depletion: How to Handle the Misconceptions. World J Nephrol: 8(1), pp 23-32.

[9] Adrogué, H, J and Madias, N, E. (2000). Hypernatremia. The New England Journal of Medicine.

[10] Kooman, J, P., van der Sande, F, M and Leunissen, K, M. (2004). Sodium, Blood Pressure and Cardiovascular Pathology: Is It All Volaemia? Nephrology Dialysis Transplantation: 19(5), pp 1046-1049.

[11] Adrogué, H, J and Madias, N, E. (2000). Hypernatremia. The New England Journal of Medicine.

[12] British Heart Foundation. (2018). Salt. Available at:

[13] Montain, S, J., Cheuvront, S, N and Sawka, M, N. (2006). Exercise Associated Hyponatraemia: Quantitative Analysis to Understand the Aetiology. Br J Sports Med: 40(2), 98-105.

View full list of biomarkers

This information has been medically reviewed by Dr Nicky Keay

Nicola has extensive clinical and research experience in the fields of endocrinology and sport and exercise medicine. Nicky is a member of the Royal College of Physicians, Honorary Fellow in the Department of Sport and Exercise Sciences at Durham University and former Research Fellow at St. Thomas' Hospital.

Dr Nicky Keay

Dr Nicky Keay

BA, MA (Cantab), MB, BChir, MRCP.