Understanding low sodium levels in older people

Reviewed by Dr Patrick Ruane

Is your parent or elder relative at risk for low sodium levels? Or have you been told their sodium is low?

Blood sodium levels tend to decrease with age for a range of reasons. It can be a side effect of medication or a consequence of certain medical conditions like kidney disease. It is especially common in older people who are in care homes or hospitals. However, it can be hard to spot and is usually only discovered incidentally through routine blood tests.

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Read on to learn more about about low blood sodium levels and how it can be prevented and treated in older people.

Note: If you think your elderly parent or loved one might be at risk or suffering from low sodium levels, you should speak to their doctor to arrange for a blood test.

Why are low sodium levels a concern?

Sodium is an electrolyte that regulates the amount of water in and around our cells. Most of the body’s sodium is in the blood or fluid around the cells. We get our sodium through what we eat and drink, and we lose it in our sweat and urine.

Low sodium levels (known medically as hyponatremia) cause several medical conditions and health problems, ranging from mild to life-threatening. As people get old, their risk of having abnormally low blood sodium levels increases, so it is helpful to know the risks and signs of low sodium, and how it can be treated.

What are normal blood sodium levels?

Your blood’s sodium level should be between 135-145 mmol/L – this is the normal range for blood sodium levels. Your body needs sodium to function and keep the cells of your body alive. It’s one of several electrolytes in the body, such as potassium and magnesium, which are essential for various bodily functions including blood pressure control, nerve functioning and muscle movement.  

Our sodium levels are monitored and controlled by our bodies in several ways, including our feelings of thirst, two hormones called vasopressin (or anti-diuretic hormone) and aldosterone, and our kidneys.

When you have low blood sodium levels (below 135 mmol/L), your sodium is too diluted. That means you either have too much water or fluid in your body or too little sodium, or both. This causes your cells to take in too much water and start to swell, which is dangerous – particularly for the brain.

Signs and symptoms of low sodium

While there are many reasons for low blood sodium levels in older people, the most common is simply a reduced ability to excrete excess water. This can be caused by illnesses that cause a lot of fluid retention, such as heart or kidney disease. Low blood sodium can also occur when people take certain medications such as diuretics (also known as water pills) that help the body excrete fluids.

Signs and symptoms of low blood sodium levels can vary and depend on whether the levels fall suddenly or gradually over time, and whether it is mild (less than 135 mmol/L) or severe (less than 120 mmol/L).  

Signs and symptoms of low blood sodium levels include:

  • Nausea, vomiting, diarrhoea
  • Irritability, tiredness, and headache
  • Muscle cramps, weakness and confusion
  • Seizures

Why do elderly people have low blood sodium levels?

It is common for elderly people to have low blood sodium levels (especially mild low levels). Those living in care homes or in hospital are even more susceptible. This is because older people tend to have chronic diseases or be on medications that contribute to low sodium levels.

Medications associated with low blood sodium levels

  • Antidepressant drugs
  • Carbamazepine, an anti-seizure medication
  • Diuretics (used to treat high blood pressure or improve symptoms of liver or heart failure)

Conditions associated with low blood sodium levels

  • Kidney disease, liver disease and heart problems
  • Syndrome of inappropriate anti diuretic hormone secretion
  • Pneumonia or urinary tract infections
  • Under activity of the thyroid or adrenal glands
  • Severe vomiting and diarrhoea

Diagnosing low sodium levels

You should alert a doctor if you see any symptoms of low blood sodium, including nausea and vomiting, headaches/migraines, muscle cramps and spasms (especially in the legs). You should also let them know what medications and supplements your parent takes.

Several tests and tools are used to diagnose and discover the cause of low blood sodium levels, or hyponatremia to use its medical name, including:

Blood test – a simple blood test can determine whether someone has low blood sodium levels. As well as testing the sodium levels, doctors will test the blood for other things, such as levels of potassium, and indicators of kidney, adrenal and thyroid function.

Urine sample – a urine sample provides information on sodium levels, and information on how the kidneys are functioning. A doctor will take a urine sample if the blood test shows low blood sodium levels.

Imaging (e.g., X-rays or ultrasound) – these and other tests can be undertaken to look for signs of heart failure or other conditions associated with low blood sodium levels.

Treating low sodium levels

Treatment depends on the cause and severity of low sodium levels. The aim is to treat the underlying cause. A doctor will consider several treatments or combination of treatments based on this, which include:

Intravenous (IV) fluids – if the levels of sodium are very low, an IV sodium solution is usually used to bring the levels back to the normal range which requires a stay in hospital.

New medications – medications may be prescribed to treat the symptoms of the low blood sodium levels, such as headache, nausea or seizure. Other medications may be prescribed to treat heart failure, kidney or liver disease if any of these are discovered to be the root cause.

Adjusting current medications – the doctor may adjust some medications that your parent or elderly relative is on, if they believe the low sodium levels are a side effect of the medication. This can include altering the dose or switching to a different type of medication.

What to ask the doctor about low sodium levels

If your elderly parent or relative is diagnosed with hyponatremia, it is important to get the full picture of their condition. Here are some questions to consider asking their doctor:

  • What is the most likely root cause of the low sodium levels? What further investigations need to happen to find out?
  • How severe is the hyponatremia?
  • Are there any changes that can be made to their diet, medications or lifestyle to stabilise their sodium levels? Do they need to alter their fluid intake?
  • When do you expect the condition and symptoms will start to improve?
  • How can we help to prevent this from happening again? Is there anything we need to do in terms of monitoring the sodium levels or any other health signs?

How to prevent low sodium levels in the elderly

It can be difficult to prevent low sodium levels in the elderly and hard to spot the signs if the condition is mild and develops gradually. The best thing you can do is:

Monitor for and treat associated conditions – ensure your parent or relative is getting the right treatment for any chronic conditions that can cause hyponatremia, such as kidney or heart disease.

Know their medications – understand what medications your parent or elderly relative is taking and what side effects they have that you should look out for. If you’re not sure, speak to their doctor or a health professional.

Ensure balanced fluid intake – getting the right balance of fluid is difficult for older people.  Many suffer from mild dehydration as their sense of thirst diminishes. They also tend to have more frequent episodes of diarrhoea, which causes them to lose fluids and essential electrolytes, including both sodium and potassium. If your elderly parent or relative gets diarrhoea or loose bowels, you can replenish their lost fluids and electrolytes with oral rehydration salts or drinks containing electrolytes, like Coconut Water. Talk to a doctor if your parent develops severe or chronic diarrhoea.

Improving their diet – It’s important talk to their doctor before making any major changes to their diet.  For example, although salt is an important source of sodium for our bodies, salt consumption needs to be carefully managed in old age as too much salt can cause high blood pressure which leads to other health issues. Learn more at Action on Salt.

In summary

Sodium is an important electrolyte that is essential for our bodies to function normally. Low sodium levels (hyponatremia) can cause various health problems and can be dangerous.

Mild hyponatremia is a common problem in older people that can be difficult to spot, but it can be easily diagnosed with a simple blood test and treatment is available for this condition.  

Severe hyponatremia (blood sodium levels less than120mmol/L) or hyponatremia that develops quickly is dangerous and can lead to severe complications such as brain swelling, damage or coma.

If your elderly parent or relative develops symptoms of severe hyponatremia (such as nausea and vomiting, confusion or seizures), you should seek immediate emergency medical help.

Common questions

  • Should I eat more salt if my sodium is low?

There can be many reasons why someone has low sodium levels (hyponatremia), and it usually has little to do with the amount of salt in their diet. Always check with a doctor before increasing your salt intake. They can provide personalised recommendations of how to address low blood sodium levels, based on the underlying cause.

  • Is it bad if your sodium is low?

Yes, low sodium levels (hyponatremia) can cause various health problems, ranging from mild to life-threatening, especially if left untreated.

  • How can I increase my sodium levels naturally?

Increasing sodium levels should be done under medical supervision. Always consult with a healthcare professional for personalised advice based on the cause of your low sodium levels. Natural ways of increasing sodium in the blood include drinking less water or eating foods that are salty, such as olives, pickles, and certain types of fish.


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