what causes low sodium

Low sodium in the blood (hyponatremia) happens when the balance between water and sodium in the body is disrupted, most often because there is too much water relative to sodium, or because sodium is lost through illness or medications. It is usually a medical issue related to fluid balance and hormones, not simply “not eating enough salt.”

What “low sodium” means

• Hyponatremia generally means a blood sodium level below about 135 mmol/L, which disrupts how water moves in and out of cells.

• When sodium outside cells is too low, water moves into cells and makes them swell, including brain cells, which is why symptoms can be serious.

Main medical causes

Low sodium has many possible causes, but they usually fall into a few big groups.

• Too much body water (dilutional):
  • Drinking very large amounts of water in a short time (including during endurance sports) can dilute sodium.

* Conditions where the body holds on to water, such as syndrome of inappropriate antidiuretic hormone (SIADH), cause water retention and increased sodium loss in urine.

• Fluid‑overload diseases:
  • Heart failure, kidney disease, and liver cirrhosis can all cause fluid to build up in the body, diluting sodium in the bloodstream.

• Loss of sodium and fluids:
  • Prolonged vomiting, severe or chronic diarrhea, and heavy sweating (including from burns over large areas of the body) can lead to loss of sodium and water, sometimes with more sodium loss than water.

• Medications:
  • Diuretics (“water pills”), some antidepressants, pain medications, seizure medicines, and certain cancer drugs can increase sodium loss or cause the body to retain extra water.

• Hormone and endocrine problems:
  • Adrenal insufficiency (Addison’s disease) and low thyroid hormone can impair the body’s ability to regulate sodium, potassium, and water properly.

• Kidney‑related factors:
  • Kidney disease or failure can impair the kidneys’ ability to get rid of excess water or to conserve sodium appropriately, leading to low blood sodium.

• Other contributors:
  • Very high blood sugar (extreme hyperglycemia) can pull extra water into the bloodstream, contributing to low measured sodium.

* Heavy or chronic alcohol use is often linked with hyponatremia through poor nutrition, vomiting, and effects on hormones and the kidneys.

* Some recreational drugs such as MDMA/ecstasy are known to trigger dangerous, sudden hyponatremia, especially when combined with excessive water intake.

Why it matters and what to watch for

• Low sodium can cause headache, nausea, confusion, muscle cramps, and in more severe or rapid cases, seizures, coma, and can be life‑threatening.

• The same sodium level can be mild in one person and an emergency in another, depending on how fast it dropped and underlying health.

If blood work has shown low sodium, or if there are symptoms like confusion, severe weakness, or seizures, urgent medical evaluation is needed rather than self‑treating with more salt or water.

Big picture: not just “too little salt”

• In most cases, hyponatremia is more about fluid handling and hormones than actual dietary sodium deficiency.

• Determining the cause usually requires a clinician to look at:
  • Medications
  • Other illnesses (heart, kidney, liver, endocrine issues)
  • Hydration habits and recent vomiting/diarrhea or sweating.

Information gathered from public forums or data available on the internet and portrayed here.