Low sodium (hyponatraemia)

You are more likely to have low sodium as you get older, especially if you have a heart or kidney condition or take certain medications.

There are many reasons why your sodium level might get too low — these are some of the common ones.

• Taking some medications, including water pills (diuretics), some antidepressants, pain medications and epilepsy medication.
• Having heart failure, kidney disease or liver disease. These conditions can affect the amount of fluid in your body and your sodium level.
• Having bouts of long lasting, severe runny poos (diarrhoea) or throwing up (vomiting) in which you lose fluids and sodium.
• Drinking too much water, which can dilute the amount of sodium in your blood. This can be a problem in endurance events like marathons or triathlons when you also lose sodium through sweat.
• Having a hormone imbalance that affects your sodium level. This can happen with Addison's disease and an underactive thyroid gland (hypothyroidism).
• Taking ecstasy (MDMA). This recreational drug has been linked to serious cases of low sodium.

You may not have any symptoms if your low sodium is mild. You are more likely to have symptoms if your sodium drops quickly or is very low.

Signs of low sodium may include:

• feeling sick (nausea) or throwing up (vomiting)
• weakness, tiredness and low energy
• headache
• cramps or spasms in your muscles
• irritability and restlessness
• sleepiness
• confusion
• loss of consciousness or coma
• seizures.

Because the symptoms of low sodium can vary so much from person to person, a blood test is needed to make the diagnosis. You may also need a urine test.

Laboratory tests

A routine blood test that you have for other reasons may also show low sodium.

Your treatment will depend on how severe your low sodium is and what the likely cause is.

If your low sodium is mild, you may be asked to:

• cut back on how much fluid you drink
• adjust or stop any medications, such as diuretics, that can lower your sodium. 

If your low sodium is severe (very low), you may need treatment and monitoring in hospital.

• You will be given fluids into a vein (intravenously) to boost the sodium level in your blood.
• You may also be given medication to manage any symptoms such as headaches, feeling sick (nausea) or seizures.
• You may be asked to cut back on how much fluid you drink.

Other treatments aim to correct the underlying problem. They may include stopping any medication that can lower your sodium.

There are several ways you may be able to prevent low sodium.

Know the symptoms of low sodium. Watch for them if you:

• have a condition that can put you at risk
• take medications that can cause low sodium, such as diuretics.

Pay attention to how much water you are drinking, especially if you take part in high-intensity physical activities. There are 2 reliable ways to know how much water you should have, your thirst and the colour of your wee. You are probably getting enough water if you do not feel thirsty and your wee is a pale-yellow colour.

Consider taking electrolyte sports drinks if you are doing intense physical activity for longer than 1 hour, especially in hot weather.