Electrolyte Abnormalities and Eating Disorders
By Elissa Rosen, MD, CEDS-S
Electrolyte abnormalities are frequently seen in eating disorders associated with purging behaviors. (1) Electrolytes are minerals found in the body that can also be measured by blood tests. Our body is quite particular about the amount of electrolytes it needs to function properly and has different organ systems, such as the kidneys, that are designed to help maintain a narrow range of electrolyte levels in the blood.
All types of purging behaviors including vomiting, laxative use, and diuretic use can be associated with both dehydration and abnormal electrolytes. The mode and frequency of purging behaviors can certainly impact the type and degree of electrolyte derangements. With the exception of low sodium in the blood, or hyponatremia, restrictive only eating disorders, such as anorexia nervosa restrictive type, are generally not associated with electrolyte abnormalities or dehydration (unless extreme restriction of fluid is part of someone’s restrictive eating disorder behaviors).
Today, we address the major electrolyte abnormalities associated with purging as well as the possible symptoms and consequences that can occur from abnormal electrolytes. The physiology behind these abnormalities can get quite complex so we are just going to stick to the basics. Please also note that the absence of electrolyte abnormalities and/or dehydration does NOT mean that someone with an eating disorder does not need or deserve professional help.
Dehydration
All forms of purging can lead to dehydration. Dehydration occurs from loss of bodily fluids. (2) When that loss is small and sufficiently replaced with salt and water, hydration status can remain normal. During times of dehydration, the kidneys also compensate by maximally retaining salt and water rather than excreting it in the urine. However, if the fluid losses are too great, dehydration ensues. The symptoms associated with dehydration are due to decreased blood flow throughout the body. This can lead to generalized fatigue, dizziness, muscle cramping, a racing heart, fainting, and low urine output to name a few. Dehydration can be dangerous if untreated as it can cause dramatic falls in blood pressure and multiorgan failure. Weight decreases associated with purging are often just due to loss of water and subsequent dehydration. Correction of dehydration involves cessation of behaviors and either oral rehydration or intravenous infusions of saline solution depending on the severity of the dehydration.
Hypokalemia
Hypokalemia, or a low potassium level, can occur from all modalities of purging. (1) Hypokalemia occurs due to loss of potassium in vomit, urine, and/or stool. An ideal potassium level is around 4.0 mEq/L, but hypokalemia is technically defined as a potassium less than 3.6 mEq/L. Our body works really hard through both kidney and non-kidney mechanisms to maintain our serum potassium within a very narrow range, but when potassium losses are too great, blood levels will fall. As potassium levels falls below 3.0 mEq/L, symptoms generally appear. These can include muscle weakness, muscle cramping, respiratory muscle weakness (causing shortness of breath), and severely slowed digestion leading to severe constipation and abdominal distension. (3) Lastly, our heart is exquisitely sensitive to potassium levels, and when levels are too low (or too high), various cardiac arrhythmias may develop, many of which can be fatal. Treatment of hypokalemia involves cessation of behaviors that result in the loss of potassium as well as oral or intravenous replacement as directed by a medical professional.
Metabolic acidosis and alkalosis
Metabolic alkalosis or a high serum bicarbonate (often denoted as carbon dioxide on lab reports) level is one of the most common electrolyte abnormalities seen in eating disorders associated with purging via vomiting. (1) Bicarbonate helps to maintain our blood pH balance, which once again, our body likes to keep in a narrow range. The specifics of why bicarbonate rises in the setting of vomiting is a topic for another blog (if you are interested in learning more about this now, I would encourage you to explore the references listed below), but it is important to know that both vomiting and diuretic abuse can cause a rise in bicarbonate. This rise typically indicates a more alkaline blood pH and generally is a marker of dehydration in the setting of these purging behaviors. (4) A normal bicarbonate ranges from 20 to 29 mEq/L. Metabolic alkalosis in and of itself may not cause symptoms, but symptoms often emerge from concomitant dehydration and electrolyte derangements such as hypokalemia. Severe metabolic alkalosis can lead to muscle spasms and seizures. Treatment involves correcting the underlying cause (i.e., cessation in the case of vomiting and diuretic use) as well as intravenous hydration especially as the bicarbonate rises above 35 mEq/L.
Metabolic acidosis, or a low serum bicarbonate level, can occur with laxative use as bicarbonate is lost through the stool. (1) Metabolic acidosis generally reflects an underlying acidic blood pH. A mild metabolic acidosis, specifically ketoacidosis, may develop in the setting of severe caloric restriction due to the production of an alternate energy form knows as ketones. Signs of metabolic acidosis can be non-specific and again are exacerbated by other concomitant abnormalities such as dehydration and other electrolyte derangements. General symptoms can include rapid breathing, weakness, fatigue, nausea, and decreased appetite. Correction of metabolic acidosis is again aimed at treating the underlying cause. For those with ketoacidosis related to severe caloric restriction, increased nutritional intake is the solution. Cessation of laxatives and correction of volume depletion, often with intravenous fluids, can correct metabolic acidosis due to laxative abuse.
Hyponatremia
Hyponatremia or low blood sodium level can be seen in several different situations as it relates to eating disorders. Blood sodium levels are not a reflection of the amount of salt in the blood, but rather reflects the ratio of water to salt. (4) Normal blood sodium levels range from 135-144 mEq/L. Purging of all modalities can lead to hyponatremia due to loss of salt and water (aka: dehydration or volume depletion). Hyponatremia can also be seen in severe restrictive eating disorders due to decreased ability of the kidney to excrete free water as a result of low nutritional intake. Without enough food or solutes, even a fairly normal amount of water intake can lead to hyponatremia if the body retains too much of it. Increased nutritional intake and a temporary fluid restriction while working on increasing nutrition can correct hyponatremia in this situation.
Certain psychiatric medications, including serotonin reuptake inhibitors (SSRIs), may cause hyponatremia in some individuals through a mechanism called the syndrome of inappropriate antidiuretic hormone (SIADH). Antidiuretic hormone (ADH) causes the reabsorption and retention of water by the kidneys. Some medications can cause increased release of ADH leading to increased retention of water and dilution of the blood which can cause hyponatremia. SIADH due to medications is corrected by temporary fluid restriction and cessation of causative medications. Psychogenic polydipsia, or an often insatiable craving to drink water, can lead to severe hyponatremia especially as water consumption levels get higher. While not correlated with eating disorders, I have certainly seen patients with psychogenic polydipsia and eating disorders. (4)
Medically, hyponatremia can be very dangerous both in its development and treatment. Symptoms of hyponatremia are more pronounced if the drop in sodium is sudden and/or rapid (acute hyponatremia) versus more a slow, chronic drop (chronic hyponatremia). (5) Symptoms generally develop as sodium levels drop below 120 mEq/L. Acute hyponatremia can cause seizure, confusion, coma, and respiratory failure. Hyponatremia can also lead to brain swelling and herniation, which is fatal. Chronic hyponatremia often has more subtle symptoms such as headache, lethargy, nausea, vomiting, dizziness, and muscle cramps. Correction of hyponatremia must be done under the guidance of a medical professional and in a hospital setting (often times in an intensive care unit or ICU) when severe. Particularly with chronic hyponatremia, correction of low sodium must be done very slowly to avoid a permanent brain complication called central pontine myelinolysis (CPM), which in severe cases can cause someone to be fully awake, but unable to move or speak. This is also known as “locked in’’ syndrome. Methods to correct hyponatremia depends on the cause and again should always be guided by a medical professional as there can often be a complex overlay of factors that are contributing to hyponatremia. Due to this, the treatment plan is not always straightforward and needs to be tailored based on the individual’s clinical presentation, physical examination, and other supporting lab work.
References:
1. Mehler PS, Walsh K. Electrolyte and acid-base abnormalities associated with purging behaviors. Int J Eat Disord. 2016 Mar;49(3):311-8. doi: 10.1002/eat.22503. Epub 2016 Feb 15. Review. PubMed PMID: 26876281.
2. Sterns, Richard. Etiology, Clinical Manifestations, and diagnosis of volume depletion in adults. Up to Date Online. 2018.
3. Mount DB. Clinical manifestations and treatment of hypokalemia in adults. Up to Date Online. 2017.
4. Gaudiani, JL. Sick Enough: A guide to the medical complications of eating disorders. New York, NY: Routledge, 2019.
5. Sterns, RS. Overview of the treatment of hyponatremia in adults. Up to Date Online. 2018. Routledge. 2019.