Hyponatraemia causes overview

Overview

Hyponatraemia is a condition where the level of sodium in your blood is too low. Sodium helps control the amount of water in and around your cells. When sodium is low, your body’s water balance is upset, which can cause cells to swell. This can be dangerous, especially for brain cells.

Yes, it is quite common. It affects about 1 in 5 people in the hospital and up to 1 in 3 older adults in long-term care.

It can affect people of any age, but it is more common in older adults, people with chronic illnesses (like heart failure or kidney disease), and those taking certain medicines.

Symptoms

Common symptoms

• Nausea and vomiting
• Headache
• Confusion or difficulty concentrating
• Fatigue and weakness
• Muscle cramps or spasms

Symptoms in children

• Irritability or fussiness
• Poor feeding or refusing to eat
• Unusual drowsiness

Symptoms in older adults

• Increasing confusion or memory problems
• Unsteady walking or falls
• Loss of appetite

Causes

Main causes

• Drinking too much water (for example, during endurance sports like a marathon, or in some mental health conditions).
• Taking certain medicines, such as water pills (diuretics), some antidepressants, or painkillers like ibuprofen.
• Medical conditions that cause the body to hold onto water, such as heart failure, liver cirrhosis, kidney disease, or the syndrome of inappropriate antidiuretic hormone (SIADH).
• Hormonal imbalances, like an underactive thyroid (hypothyroidism) or adrenal gland problems (Addison's disease).
• Severe vomiting or diarrhoea that leads to loss of salts.

Risk factors

• Being over 65 years old
• Taking multiple medications, especially water pills or antidepressants
• Chronic health conditions (heart, kidney, liver, or lung disease)
• Recent surgery or hospital stay
• Drinking large amounts of water without enough salt intake

When to see a doctor

See a doctor urgently if:

• If you have a seizure or lose consciousness, call your local emergency number immediately.
• If you have severe headache, repeated vomiting, or sudden confusion, go to the emergency department or seek urgent care.

Book a routine appointment if:

• If you have ongoing nausea, headache, or fatigue that does not get better.
• If you are at risk (for example, taking diuretics or having a chronic illness) and you feel unwell.
• If you have recently had a test showing low sodium and want to discuss next steps.

Diagnosis

Hyponatraemia is diagnosed with a simple blood test that measures the amount of sodium in your blood. Your doctor may also check your urine and ask about your medical history and medicines.

Tests that may be done

• Blood sodium level (a blood test from a vein in your arm)
• Urine sodium and osmolality (to see how your kidneys are handling water and salt)
• Blood tests for kidney function, thyroid levels, and adrenal hormones (if needed)

What to expect at your appointment

The blood test is quick and usually painless. Results often come back in a few hours. Your doctor will explain what your number means and whether you need any further tests or treatment.

Treatment

Treatment depends on what is causing the low sodium, how low it is, and how fast it dropped. The main goal is to slowly raise the sodium level to a safe range while fixing the underlying cause.

Self-care at home

• Follow your doctor’s advice about how much fluid to drink each day—sometimes you may need to reduce water intake.
• Avoid drinking large amounts of water during exercise; replace lost fluids with a balanced sports drink or salt-containing fluids as guided.
• If you have vomiting or diarrhoea, use oral rehydration solutions (ask your pharmacist) to replace both water and salts.

Medical treatments

For mild cases, treatment may involve adjusting or stopping certain medicines, changing how much fluid you drink, or treating the underlying condition (such as heart failure or hypothyroidism). For moderate or severe hyponatraemia, doctors may prescribe intravenous fluids containing sodium or give medicines to help your body get rid of extra water. This is usually done in a hospital so the sodium level can be corrected slowly and safely.

When is surgery considered?

Surgery is not typically used to treat hyponatraemia itself, but if the cause is a tumour or other surgical condition (for example, a tumour producing ADH), that underlying problem may need surgery.

Living with this condition

If you have chronic low sodium, you may need regular blood tests to check your levels. Your doctor will help you create a plan that fits your life. Stay in touch with your healthcare team and let them know if you feel different.

Lifestyle tips

• Try to keep a consistent fluid intake—not too much, not too little.
• Avoid extreme exercise without proper hydration planning.
• If you take water pills or other medicines, take them exactly as prescribed and report any side effects.

Diet and exercise

Eat a balanced diet with enough salt (sodium) as advised by your doctor—this may mean not restricting salt unless told otherwise. During exercise, drink when thirsty and consider a sports drink if you sweat a lot. For most people, plain water is enough, but if you are prone to hyponatraemia, follow a personalised plan.

Mental health and emotional wellbeing

Living with a chronic condition can feel worrying or stressful. It is normal to have questions or feel anxious about your sodium levels. Talk to your doctor about your concerns. If you feel overwhelmed, consider speaking with a counsellor or joining a support group.

Prevention

In many cases, yes. You can reduce your risk by not overdrinking water (especially during endurance sports), telling your doctor about all medicines you take, and managing chronic conditions like heart or kidney disease. If you are at higher risk, your doctor may check your sodium levels regularly.

Screening programmes

There is no routine screening for the general public. However, if you are in hospital or have a condition that raises your risk, your healthcare team will check your sodium levels as part of standard care.

Complications

If left untreated

• Brain swelling (cerebral oedema) leading to confusion, seizures, and coma
• Bone thinning (osteoporosis) with long-term low sodium
• Increased risk of falls and fractures, especially in older adults
• In very severe cases, death

Long-term outlook

With prompt and careful treatment, most people recover fully from hyponatraemia. If the underlying cause is found and managed, sodium levels usually return to normal. For chronic conditions, working closely with your healthcare team can keep your levels stable and prevent complications.

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