Low levels of sodium in the blood, a condition known as hyponatremia, may be an indicator that the body is retaining rather than excreting excess water; this may be the result of an overproduction of the anti-diuretic hormone, states Mayo Clinic. Hyponatremia may also be the result of dehydration.
Normal blood sodium levels typically range from 135 to 145 milliequivalents per liter; proportions below 135 milliequivalents per liter are considered abnormal, Mayo Clinic advises.
A wide range of factors are responsible for hyponatremia, explains Mayo Clinic. These include the use of recreational drugs such as the amphetamine ecstasy and even consuming extremely high amounts of water. Medications that increase urination or perspiration, such as analgesics, diuretics and antidepressants, can also trigger the condition. Certain hepatic, cardiac and renal conditions may cause excessive water retention, diluting the amount of sodium in the body. Hyponatremia may also be the result of the electrolyte and fluid loss that accompanies severe diarrhea and vomiting.
Low blood sodium levels may also be the product of hormonal changes, states Mayo Clinic. Depressed levels of the thyroid hormone, which is responsible for controlling the body's metabolism and other functions of the body, and malfunctions of the adrenal gland, which is a critical part of the body's sodium, potassium and water regulation mechanism, may give rise to hyponatremia.