Plasma sodium refers to the concentration of sodium in the blood, a measurement reflecting the body’s fluid and electrolyte balance. Maintaining this level supports numerous biological processes. Deviations from the normal range, typically 136-145 millimoles per liter (mmol/L), can have significant health implications. The body continuously works to keep plasma sodium within this narrow window, influencing overall physiological stability.
The Body’s Essential Sodium Functions
Sodium plays a comprehensive role in maintaining the body’s internal environment, extending beyond just fluid regulation. It is a positively charged electrolyte found predominantly in the fluid surrounding cells. This positioning allows it to influence water distribution both inside and outside cells, which in turn impacts blood volume and blood pressure.
Beyond fluid dynamics, sodium is important for nerve impulse transmission. Electrical signals in nerves rely on the movement of sodium ions across cell membranes, enabling communication throughout the nervous system. This electrical activity is also directly linked to muscle function, as sodium is involved in muscle contraction and relaxation. The precise balance of sodium, often facilitated by the sodium-potassium pump, ensures these movements and signals occur.
When Sodium Levels Are Too Low
When plasma sodium concentration drops below 135 mmol/L, the condition is known as hyponatremia. This imbalance occurs when there is either too much water relative to sodium in the blood, or not enough sodium. Mild hyponatremia is defined as levels between 130-134 mmol/L, while severe cases are below 125 mmol/L.
Several factors can lead to hyponatremia. Excessive water intake, particularly during intense exercise, can dilute sodium levels in the blood. Certain medications, such as diuretics and some antidepressants, can also contribute to this condition. Underlying medical conditions like heart failure, kidney disease, liver cirrhosis, and specific hormonal imbalances, such as the syndrome of inappropriate antidiuretic hormone (SIADH), are also common causes.
Symptoms of hyponatremia vary depending on the severity and speed of the sodium drop. Mild symptoms include nausea, vomiting, headache, and fatigue. As sodium levels fall further or more rapidly, symptoms can progress to more severe neurological manifestations, such as confusion, irritability, muscle cramps or spasms, and even seizures or coma. Due to potential serious complications, including brain swelling in acute cases, hyponatremia requires prompt medical evaluation and management.
When Sodium Levels Are Too High
Conversely, hypernatremia occurs when plasma sodium levels rise above 145 mmol/L. This indicates a deficit of total body water relative to sodium. While symptoms can occur at levels above 145 mmol/L, severe symptoms manifest when levels exceed 160 mmol/L.
The primary cause of hypernatremia is severe dehydration, resulting from insufficient water intake or excessive fluid loss. This fluid loss can happen due to prolonged vomiting, severe diarrhea, or high fevers. Certain medical conditions like diabetes insipidus, which impairs the body’s ability to conserve water, can also lead to hypernatremia. Excessive salt intake or specific adrenal gland disorders may also contribute.
Symptoms of hypernatremia are largely related to the body’s dehydration and the impact on brain cells. The most common symptom is intense thirst. As the condition worsens, individuals may experience lethargy, confusion, and muscle twitching or spasms. In severe cases, brain cell shrinkage can lead to seizures, coma, and even death. Prompt medical attention is necessary for hypernatremia to prevent serious neurological complications, with treatment involving the gradual replacement of fluids.
Keeping Your Sodium Levels Balanced
The body maintains plasma sodium within its healthy range through various mechanisms. The kidneys play a central role, adjusting the amount of sodium excreted in urine to match daily intake. This renal regulation is supported by the thirst mechanism, which prompts fluid intake when plasma osmolality, primarily influenced by sodium, increases.
Hormones also contribute to this balance. Antidiuretic hormone (ADH), also known as vasopressin, is released in response to increased plasma osmolality or decreased blood volume. ADH causes the kidneys to reabsorb more water, thereby diluting plasma sodium. Another hormone, aldosterone, secreted by the adrenal glands, signals the kidneys to retain sodium, which helps increase blood volume.
To support these natural regulatory processes, maintaining adequate hydration and consuming a balanced diet are recommended. While the body needs a small amount of sodium (less than 500 mg per day), most individuals consume much more, around 3,400 mg daily from processed foods. If symptoms related to sodium imbalances arise, seeking professional medical advice is recommended over attempting self-treatment.