Sodium
SODIUM
Sodium is the sixth most common element found in the earth's crust. It is also one of the primary macrominerals. Its chemical symbol is Na. Sodium occurs in all animals and in many plants as salt, or sodium chloride (NaCl). An adult human weighing 70 kg contains approximately 100 g of sodium, 40 % located in the bones and 60 % in the cellular and intercellular fluids.
Sodium (and chloride) functions in the extracellular fluid, regulating blood pressure and extracellular fluid volume. This includes blood plasma, interstitial (intercellular) fluid, and transcellular fluid (cerebrospinal fluid, synovial fluid, etc.). Regulating this balance is crucial for the cell membrane potential and the sodium-potassium-ATPase pump (see section “Potassium” for more information). The function and number of these pumps vary by physical activity, fasting, age, various hormones, and medication. Sodium is the major cation in the extracellular fluid (cf. potassium being the major cation in intracellular fluid). Its presence outside cells is 10 times higher than inside cells.
HYPONATREMIA
Hyponatremia, or low sodium levels in the blood, may develop for various reasons. Generally, the body strives to maintain a steady sodium level in the blood. Hyponatremia is very rarely caused by insufficient sodium in the food. Excessive sodium in the food does not lead to excessive sodium in the blood, as the excess sodium is filtered by the kidneys.
In practice, hyponatremia can develop in two ways: due to severe sodium loss or excessive water in the body (dilutional hyponatremia). In the latter, all body fluids are diluted, causing a decrease in sodium levels. Usually, hyponatremia is caused by excessive water in the body. Hyponatremia caused by sodium loss may occur after several days of severe diarrhea and vomiting. This usually requires hospital care and intravenous hydration. Hyponatremia is more common in the elderly, particularly in individuals with long-term illnesses such as cardiovascular disease, cancer, or diabetes.
Hyponatremia symptoms include:
- Headache
- Nausea and vomiting
- Muscle cramps
- Fatigue
- Disorientation
- Fainting
Many drugs form a predisposing factor for hyponatremia, particularly when taken in large doses over a long time. These include diuretics, ACE inhibitors, anti-inflammatory drugs, opiate-based analgesics, SSRIs, tricyclic antidepressants, carbamazepine, and lamotrigine. Another predisposing factor for hyponatremia is excessive endurance training, often involving excessive drinking.
HYPERNATREMIA
Hypernatremia, or high sodium levels in the blood, may develop for various reasons. The blood sodium level increases when the individual is dehydrated i.e. has insufficient water intake or loses excessive amounts of water through the kidneys. This does not occur in a healthy individual, as the thirst center in the brain activates and dehydration is prevented by drinking water. If the thirst center does not function properly and insufficient water intake, the resulting consequences may include dehydration and hypernatremia. This may occur, for example, in elderly individuals with anomalies in brain function. Sometimes hypernatremia may also occur in connection with severe diarrhea and vomiting, causing excessive water loss.
A significant majority of sodium intake comes from the salt contained in food. However, excessive sodium intake from food does not cause hypernatremia in healthy individuals. This is because sodium-rich food causes thirst, increasing water intake. At the same time, the kidneys filter excessive sodium. Severe hypernatremia involves blood sodium levels over 155 nmol/L (the normal range being 137–145 nmol/L).