Low sodium in the body, also known as hyponatremia, is caused by hormonal changes; dehydration; heart, kidney and liver problems; or chronic, severe diarrhea or vomiting, according to Mayo Clinic. Some medications, such as antidepressants, pain relievers and water pills may also cause low sodium levels.
People who drink too much water may be at risk for developing low sodium levels because too much water during rigorous activity can dilute sodium within the blood, explains Mayo Clinic. Individuals affected by syndrome of inappropriate anti-diuretic hormone may experience low levels of sodium because the high levels of hormones produced cause the body to retain water when it should be excreted normally through urine.
Hormonal changes such as an adrenal gland insufficiency can affect the body's ability to produce hormones that maintain a healthy level of water, potassium and sodium, thus lowering the blood's sodium level, states Mayo Clinic. People with low levels of thyroid hormones may also experience low blood sodium levels. Heart, liver and kidney diseases can cause the level of sodium to decrease as well. People with congestive heart failure, kidney and liver diseases may have an excess of fluid accumulating in the body that dilutes the sodium within the body.