Medical Matters > Symptoms: Hyponatraemia (Low sodium levels)

ME Essential Winter 2023


I’ve been feeling generally unwell and more fatigued – mentally and physically, for the past few months.
My GP ordered some routine blood tests – all of which were normal apart from having a slightly lower than normal level of sodium in the blood. My GP isn’t too concerned and is going to repeat the blood test. Could a low sodium level be caused by having ME?


The level of sodium in the blood has to be well controlled because having a level that is too low or too high can both cause problems.

Having a low level of blood sodium is known as hyponatraemia. This is defined as having a blood test result of less than 135 mmol/litre. Mild hyponatraemia is normally defined as 125 – 135 mmol/litre and moderate hyponatraemia is 115-125 mmol/litre. Severe hyponatraemia, which requires urgent medical attention, is defined as less than 115 mmol/litre.

Having a low blood sodium level can cause a number of symptoms – some of which also occur in ME/ CFS. Common ones include:

  • Cognitive dysfunction and fatigue – including memory problems and difficulty concentrating
  • General fatigue
  • Headaches
  • Muscle cramps and weakness

Untreated hyponatraemia can also lead to walking abnormalities and weaker bone structure with a risk of falls and fractures. Chronic or more severe hyponatraemia can cause serious neurological problems – including seizures.

To go back to your question: ME/CFS does not cause a drop in sodium levels. However, there are a number of medical conditions and drugs that cause low sodium levels. Some of these medical conditions also cause fatigue and ME/CFS-like symptoms. So these conditions should always be considered if someone with ME/CFS has a low sodium level.

  • Medical conditions and drugs that can cause low sodium levels include:
  • Diuretic (water-losing) drugs, ACE inhibitors (for high blood pressure) and SSRIs (antidepressants)
  • Drinking too much water Diarrhoea and/or vomiting
  • Kidney and liver disease
  • Addison’s disease (low levels of cortisol)
  • Hypothyroidism (low thyroid function)

So, someone has a persistently low level of sodium in the blood, this is what your GP should do. It’s important to take a full clinical history, do a physical examination and check liver, kidney and thyroid gland function, adrenal gland function (with an 8am cortisol level test) and blood markers for infection.


Information provided by The ME Association should not be construed as medical advice. Don't assume any new or worsened symptoms are simply the result of having ME/CFS or Long Covid. We recommend that any information you deem relevant is discussed with your NHS GP as soon as possible. It is important that you seek personalised medical advice from the GP who is in charge of your care and who knows you well.

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