Your body needs a certain amount of potassium in order to function. That means not too little — nor too much — of this mineral and electrolyte, which is essential for everything from nerve, muscle and heart health to keeping your fluids balanced, according to the Merck Manual.
Most of the time, your kidneys do a good job of regulating potassium levels. According to Gerald Hladik, MD, chief of the Division of Nephrology and Hypertension at the University of North Carolina School of Medicine in Chapel Hill, normal potassium levels should stay between about 3.8 and 5 millimoles per liter (mmol/L).
Having very low potassium levels is known as hypokalemia. Although hypokalemia is not common, if left untreated for too long, it can cause serious and even life-threatening consequences, including cardiac arrest. A potassium deficiency can occur for many reasons, including taking diuretics, excess sweating, vomiting or diarrhea, according to the Mayo Clinic.
Fortunately, most cases of potassium deficiency are mild, according to the National Center for Biotechnology Information. Low potassium symptoms usually depend on how bad the deficiency is. Even so, according to the Merck Manual, mild potassium deficiencies and sometimes even more severe deficiencies often don't have any symptoms at all. And when symptoms do appear, Dr. Hladik says, they can be very vague.
Signs of Low Potassium
1. Muscle Cramps and Weakness
One of the main roles of potassium is helping your muscles contract. Muscle cramps and weakness can be signs of hypokalemia, as can muscle twitches, seizures and, in extreme cases, rhabdomyolysis (death of muscle fiber, which releases toxins into the blood) and paralysis, according to the Merck Manual.
Muscle symptoms may be especially pronounced when you're exercising, per the National Organization for Rare Disorders (NORD). That's because during physical activity, your muscles need to release potassium in order for the blood vessels to dilate and ensure that enough blood flows to the different parts of your body. Not enough circulating blood, and therefore oxygen, causes muscles to react with spasms and other symptoms.
2. An Abnormal Heart Rhythm
Another primary function of potassium is to help control the electrical impulses that keep your heart beating. Low potassium levels interfere with this role and can lead to abnormal heart rhythms, particularly among people who already have a heart condition, according to the U.S. National Library of Medicine (NLM). These abnormal rhythms, such as extra beats, can be life-threatening, says Dr. Hladik. Other symptoms may include feeling faint or lightheaded, per the NLM.
3. Needing to Urinate a Lot
Hypokalemia can also affect the kidneys, which are normally responsible for keeping your body's potassium levels stable. Symptoms could include frequent urination as well as drinking a lot of water, according to the Merck Manual_._ Excessive urination is also one of the ways you can lose potassium, Dr. Hladik adds.
Read more: Daily Water Intake and Frequent Urination
4. Fatigue and GI Issues
People with slightly lower potassium levels may feel tired, according to the Mayo Clinic. And one sign that hypokalemia has affected your gut is constipation, according to an April 2018 report in Endocrine Connections. The NORD cites nausea, vomiting and loss of appetite as other possible symptoms.
How to Treat Low Potassium Levels
Doctors treat hypokalemia by giving you extra potassium. If the deficiency is severe, this is often done through an intravenous infusion, Dr. Hladik says. "With more mild degrees in low potassium when you usually don't have symptoms, we can provide oral supplementation, usually potassium chloride," he adds.
Hypokalemia without symptoms is sometimes picked up on blood tests, according to the Mayo Clinic. Once potassium levels rise to normal, the symptoms (if there are any) should go away.
Any underlying conditions also need to be addressed. This could mean changing medications, per the Mayo Clinic. Or, it may involve treating one of the conditions, like kidney failure, that can contribute to potassium deficiencies.
- Merck Manual: “Overview of Potassium's Role in the Body”
- National Center for Biotechnology Information: “Hypokalemia”
- National Organization for Rare Disorders: “Hypokalemia”
- Mayo Clinic: “Low Potassium (Hypokalemia)”
- Endocrine Connections: “Hypokalemia: A Clinical Update”
- U.S. National Library of Medicine: "Low Blood Potassium"
- Merck Manual: "Hypokalemia (Low Level of Potassium in the Blood)"