Normal sodium levels in the blood range between 135 and 145 millimoles per liter (mmol per L). If your sodium levels drop below 135 mmol per L, it's called hyponatremia. In severe cases, low sodium levels can cause neurological symptoms, brain damage and even death if left untreated.
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Here's a look at some of the dangers that are associated with low sodium levels.
Low Sodium Levels Are Dangerous for Your Brain
According to the U.S. National Library of Medicine, hyponatremia is most dangerous when the sodium level in the blood drops significantly in less than 48 hours (called acute hyponatremia).
Causes of acute hyponatremia can include excessive water intake (often in people with severe mental illness or developmental disability), use of the recreational drug ecstasy, receiving hypotonic fluid during surgery or extreme physical activity such as running a marathon, per Merck Manuals. The condition can also occur from diarrhea, sweating or vomiting.
In contrast, when the sodium level falls gradually over days or weeks (chronic hyponatremia), your body has time to make adjustments, so you may only experience mild symptoms. This version of the condition is most often seen in people with heart failure, liver failure or lung cancer.
A rapid decline in sodium levels is particularly dangerous to your brain. Hyponatremia causes water to move out of the bloodstream and into tissue cells, causing them to expand. While most of the tissue in your body can accommodate this swelling, it is a major problem for your brain.
"It is a big deal if the cells in your brain expand, because your brain is contained in a fixed space and doesn't have anywhere to go," explains nephrologist Daniel Weiner, MD, FASN, an associate professor at Tufts University School of Medicine and a member of the American Society of Nephrology's Quality Committee. As the brain tissue swells — which is called cerebral edema — it pushes up against your rigid skull and the pressure on your brain increases. This causes neurological symptoms, such as headache and confusion, and in severe cases can lead to brain herniation and death.
However, in cases of chronic hyponatremia, your brain has mechanisms that allow it to adapt to lowered sodium levels with little swelling. According to a January 2018 article in Kidney International Reports, that's why even severe cases of chronic hyponatremia aren't usually life-threatening.
Still, those with chronic hyponatremia often fare worse than other people. "It's a bad prognostic sign," Dr. Weiner says.
However, it's not fully known whether chronic hyponatremia itself has negative effects on health, apart from whatever underlying problem is causing the hyponatremia. "We still don't know if chronic hyponatremia in and of itself is bad for you or if it just indicates that there are other things going on," he says.
Who Is Most at Risk?
According to the Mayo Clinic, people who are premenopausal appear to be at the greatest risk of brain damage from hyponatremia, perhaps because of the role of estrogen and progesterone in regulating sodium levels.
Hyponatremia symptoms are also more likely to be severe in children, according to American Family Physician. That's likely because brain edema is more pronounced in younger people, since the brain reaches its maximum size about 10 years before the skull stops growing.
Per the Mayo Clinic, people with hyponatremia can experience symptoms that include:
- Nausea and vomiting
- Loss of consciousness
- Muscle weakness and spasms
If you have symptoms of hyponatremia, seek medical attention right away. How hyponatremia is treated depends on the underlying cause and the severity of symptoms.
Read more: How Much Sodium Is Lost During Exercise?
Osmotic Demyelination Syndrome
Rarely, the treatment of hyponatremia can also lead to neurological damage.
If chronic hyponatremia is treated too aggressively, it may cause sodium levels to increase too rapidly and result in osmotic demyelination syndrome, per the U.S. National Library of Medicine. Also sometimes known as central pontine myelinolysis, it is caused by the destruction of the myelin sheath that covers nerve cells in the middle of the brainstem.
According to American Family Physician, symptoms of osmotic demyelination syndrome usually occur one to six days after correcting sodium levels. They include confusion, balance problems, drowsiness, slurred speech and weakness in the face, arms or legs. The nerve damage caused by osmotic demyelination syndrome is often irreversible. Patients with alcoholism, malnutrition and advanced liver diseases are at increased risk.
It is important to note that this syndrome is rare and typically results as a complication of treatment for other problems beyond low sodium levels. Since the risk of developing this syndrome is low, it should not prevent you from seeking treatment for hyponatremia.
- American Family Physician: "Management of Hyponatremia"
- U.S. National Library of Medicine: "Low Blood Sodium"
- Mayo Clinic: "Hyponatremia"
- U.S. National Library of Medicine: "Osmotic Demyelination Syndrome"
- Journal of Clinical Medicine: "Effects of Hyponatremia on the Brain"
- Kidney International Reports: "Hyponatremia and the Brain"
- Cleveland Clinic: "Hyponatremia"
- Merck Manuals: "Hyponatremia"
Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.