Sodium

What it is

Sodium is a mineral that plays a vital role in many of your body's functions. It's one of the most important electrolytes, which are substances that carry an electric charge when dissolved in body fluids like blood. You get sodium from the food you eat and the drinks you consume. Your body needs a certain amount of sodium to work properly. It helps to maintain the right balance of fluid inside and outside your cells, which is crucial for keeping your blood pressure stable and for your nerves and muscles to function correctly.

The amount of sodium in your blood is measured in millimoles per litre (mmol/l). In the UK, a typical reference range for sodium in the blood is usually between 133 and 146 mmol/l. This range can vary slightly depending on the laboratory that carries out the test.

Why it matters

Sodium is essential for life. It's the main electrolyte found in the fluid outside your cells and in your blood plasma. This means it's a key player in regulating the amount of water in your body. It helps to ensure that your body’s cells receive the right amount of fluid, preventing them from either shrinking or swelling.

Beyond fluid balance, sodium is critical for nerve impulses. When a nerve cell needs to send a signal, it does so by rapidly changing the electrical charge across its membrane. Sodium ions are fundamental to this process, allowing these electrical signals to travel along nerves. Similarly, sodium is involved in muscle contractions, including the beating of your heart. It also works with other electrolytes, like potassium, to maintain the correct acidity (pH) of your blood.

Because sodium is so closely linked to fluid balance, it has a direct impact on your blood pressure. When sodium levels are too high, your body tends to hold onto more water, which can increase the volume of blood in your circulation and, consequently, raise your blood pressure. Conversely, very low sodium levels can sometimes lead to a drop in blood pressure.

What can cause it to be high or low

High Sodium (Hypernatraemia)

A high sodium level in the blood, known as hypernatraemia, is less common than low sodium. It often occurs when your body loses too much water relative to sodium, or when you take in too much sodium.

• Dehydration: This is a common cause. If you don't drink enough fluids, especially during hot weather or after intense exercise, your body can become dehydrated, leading to a higher concentration of sodium in your blood.
• Kidney problems: The kidneys are responsible for filtering waste and excess substances from your blood, including sodium. If your kidneys aren't functioning well, they may not be able to excrete sodium effectively.
• Certain medications: Some medications, such as diuretics (water tablets) that don't conserve sodium, or certain hormonal treatments, can sometimes lead to higher sodium levels.
• Diabetes insipidus: This is a rare condition where the kidneys are unable to conserve water, leading to excessive thirst and urination, which can result in dehydration and high sodium levels.
• Excessive salt intake: While less common as a sole cause in healthy individuals, consuming very large amounts of salt, particularly without adequate fluid intake, can contribute to high sodium.

Low Sodium (Hyponatraemia)

A low sodium level in the blood, known as hyponatraemia, is more frequently encountered. It usually happens when there's too much water in your body relative to the amount of sodium, diluting the sodium concentration.

• Heart failure: When the heart doesn't pump blood effectively, the body may retain more fluid, diluting sodium levels.
• Kidney disease: Impaired kidney function can affect the body's ability to regulate sodium and water balance.
• Liver disease: Conditions like cirrhosis can lead to fluid retention and changes in sodium levels.
• Certain medications: Some diuretics (water tablets), antidepressants, and pain medications can sometimes cause hyponatraemia.
• Hormonal imbalances: Conditions affecting hormones like ADH (antidiuretic hormone) or those related to the adrenal glands can influence sodium levels.
• Excessive water intake: Drinking a very large amount of water in a short period, especially without sufficient electrolyte intake, can dilute blood sodium. This is sometimes seen in endurance athletes.
• Vomiting and diarrhoea: Significant loss of fluids and electrolytes through persistent vomiting or diarrhoea can lead to lower sodium levels.

Lifestyle factors that may help

Maintaining a balanced intake of sodium and fluids is key.

• Hydration: Ensuring you drink adequate fluids throughout the day is important for maintaining proper fluid balance. The amount needed can vary depending on your activity level, the climate, and your individual health.
• Dietary balance: A balanced diet generally provides the right amount of sodium. Processed foods, ready meals, and salty snacks can be significant sources of sodium, so being mindful of these can be helpful. Focusing on fresh, whole foods can support a more balanced intake.
• Moderation with salt: While sodium is essential, excessive salt intake isn't usually beneficial. Discussing your dietary habits with a healthcare professional can offer personalised advice.
• Activity levels: If you engage in prolonged or intense physical activity, especially in hot conditions, it’s important to consider fluid and electrolyte replacement. Discussing appropriate strategies for rehydration with a healthcare provider can be beneficial.

Questions to discuss with your GP

If your sodium levels are outside the typical range, or if you have concerns about your fluid balance or kidney health, there are several points you might wish to discuss with your GP:

• What might be causing my sodium level to be high or low?
• Are my current medications potentially affecting my sodium levels?
• What are the implications of my sodium level for my overall health, particularly my kidney function?
• Are there any specific dietary adjustments or fluid intake recommendations that would be appropriate for me?
• What further tests or monitoring might be needed to understand my sodium levels better?
• How do my lifestyle choices, such as diet and exercise, relate to my sodium balance?