Key Takeaways (expand)
- Chloride is the ionic form of the element chlorine, and is best known as a component of table salt (sodium chloride)!
- Chloride functions as an electrolyte—a type of mineral that can conduct electricity, giving it a role in regulating fluid balance, nerve and muscle function, blood pH, and neurotransmission.
- More specifically, chloride works in conjunction with another electrolyte, sodium, to form a major component of extracellular fluid (the liquid outside of cells in the body).
- Chloride is critical for muscle function—particularly in maintaining the resting state of muscle cells.
- In the cardiovascular system, chloride plays a special role through its involvement in the “chloride shift”—a process that prevents electric charge from building up during metabolic gas exchange.
- The stomach’s production of gastric juice requires chloride (for hydrochloric acid), making this nutrient essential for digestive system functioning.
- Chloride serves as a structural component for amylase, an enzyme that helps hydrolyze starch into sugars.
- Although sodium usually gets the blame for causing hypertension, the chloride component of table salt can also increase blood pressure, due to inhibiting renin and augmenting the activity of the sympathetic nervous system.
- There’s also some evidence that chloride could contribute to osteoporosis, due to increasing the urinary excretion of calcium and influencing the activity of osteoclasts (specialized cells that break down bone tissue).
- Although chloride deficiency is rare, when it occurs, it can disrupt the body’s acid-base balance and cause a condition called metabolic alkalosis—leading to symptoms like confusion, numbness, tingling, muscle spasms, confusion, tremors, fatigue, and irritability.
- Rich sources of chloride include ocean-derived foods like prawns, salmon, and seaweed, as well as tomatoes, olives, celery, and lettuce.
Chloride is the ionic form of chlorine—that is, a single chlorine atom with a net electric charge due to the loss of an electron. It’s probably best known as a component of table salt (sodium chloride), but this mineral also happens to be present in all body fluids, and is essential for life! Chloride (as chlorine) was first isolated in 1774, when a chemist named Carl Wilhelm Scheele heated hydrochloric acid with manganese oxide, resulting in a greenish-yellow gas that ultimately inspired its name (from the Greek word khlōros, meaning “pale green”). But, it wasn’t until 1810 that the famous English chemist Sir Humphry Davy concluded it was an actual element. In fact, it took many more years before other chemists were willing to accept its status as an element, too!
Importantly, this nutrient functions as an electrolyte—a class of minerals that dissociate into charged particles (called ions) when dissolved in solution, making them capable of conducting electricity. On the whole, electrolytes help regulate fluid balance within the body, regulate nerve and muscle function (including the heart!), maintain a normal blood pH, and transmit nerve signals!
Chloride is also required for the production of hydrochloric acid in the stomach, giving it a major role in the functioning of the digestive system.
Foods high in chloride ions include prawns, salmon, seaweed, tomatoes, olives, celery, and lettuce—although most foods contain at least small amounts. Likewise, foods processed or prepared with table salt contain chloride.
The Biological Roles of Chloride
Along with sodium, chloride serves as a major electrolyte in extracellular fluid (the liquid outside of cells). In fact, after sodium, it’s the second most abundant electrolyte in serum! The kidneys tightly control chloride levels in the blood by increasing or decreasing chloride excretion to compensate for dietary intake.
Sodium and chloride have a close relationship with each other when it comes to controlling blood pressure and the amount of fluid outside of cells. Urinary secretion of sodium and chloride are closely correlated, and chloride enables the reabsorption of sodium filtered from the urinary tubules into extracellular spaces in the body. Both of these minerals are involved in the renin-angiotensin-aldosterone system, with chloride concentration inversely regulating renin secretion, and renin secretion ultimately dictating how much sodium and water gets retained. In addition, because sodium and chloride are so commonly consumed together (in the form of table salt), it’s sometimes difficult to scientifically assess the individual effects of sodium versus chloride!
Like other electrolytes, chloride contributes to muscle function, and is particularly important for maintaining the resting state of muscle cells. It’s also involved in the excitability and fatigue of muscle fibers, and is needed for electrical activity within the body (not only for skeletal muscle, but also for the heart!). What’s more, chloride plays a special role in the cardiovascular system through its involvement in the “chloride shift”—a process that helps prevent a buildup of electric charge during gas exchange. Essentially, carbon dioxide produced during cellular respiration gets expelled into the blood plasma, where it then moves into red blood cells (erythrocytes) and gets converted into carbonic acid (via an enzyme called carbonic anhydrase), after which it dissociates into bicarbonate ions. In order for the bicarbonate to exit the cell and return to the blood plasma, a chloride ion gets brought across the red blood cell membrane while a bicarbonate ion leaves. This ion exchange is what we call the “chloride shift!”
Chloride also serves as the key electrolyte for maintaining the acid-base balance in the body, preventing either metabolic acidosis or alkalosis. Additionally, it’s a structural component of certain proteins, including amylase (an enzyme that catalyzes the hydrolysis of starch into sugars). In the form of hydrochloric acid, chloride also serves as a component of gastric juice, which in turn helps digest and absorb nutrients from food.
Problems From Too Much Chloride
Because chloride consumption correlates so strongly with sodium consumption (since they’re paired up together in table salt), the independent effects of chloride have sometimes been hard to assess. However, we do have evidence that it plays some important roles in human health and chronic disease!
Chloride, Hypertension and Cardiovascular Disease
Many studies suggest that chloride is involved in the blood-pressure-raising effects typically attributed to sodium. Rodent models of hypertension show that sodium-induced elevations in blood pressure occur most strongly when both sodium and chloride are present (versus sodium alone), that both sodium chloride and chloride alone inhibit renin, and that chloride itself can raise blood pressure due to augmenting the activity of the sympathetic nervous system. And, human studies going as far back as 1929 have demonstrated that sodium in chloride-free forms doesn’t have the same blood-pressure-raising effect as sodium bound to chloride. For example, several trials of patients with hypertension found that supplementing the diet with sodium phosphate, sodium bicarbonate, or sodium citrate didn’t cause any increase in blood pressure, but supplementing with an equal amount of sodium chloride did. What’s more, these effects occurred independently of potential confounders known to affect blood pressure, like sodium or potassium balance, caloric intake, or weight gain! The effects of chloride seem particularly pronounced in people traditionally considered “salt-sensitive” (that is, people who respond to increases in salt intake with an elevation in blood pressure).
Other research offers additional support for a role of chloride in cardiovascular health. A randomized crossover study found that participants’ post-meal heart rates were strongly influenced by how much chloride was in the food they ate—possibly due to chloride’s effects on the sympathetic nervous system and/or cardiac conduction system. Recent evidence also shows that chloride is involved in the processes associated with heart failure, likely because of its role in regulating both vascular and cellular fluid balance.
In contrast to dietary intake, blood levels of chloride tend to be negatively associated with cardiovascular disease risk and mortality. One study found that among nearly 13,000 patients with hypertension, blood levels of chloride were inversely associated with both all-cause mortality and cardiovascular disease mortality; in fact, with every 1 mEq/L increase in serum chloride, mortality risk dropped by 1.5%. Studies of patients with heart failure likewise show that low serum chloride is a significant prognostic marker for poor survival, and that low chloride levels account for the majority of the risk usually attributed to low sodium. In people with chronic kidney disease, low blood chloride has been associated with a higher of risk cardiovascular events and death—with patients in the lowest quartile of serum chloride having a 248% greater risk of all-cause mortality compared to patients with higher serum chloride. Low chloride levels have also been associated with poorer functional outcomes and greater mortality risk among stroke patients, greater incidence of dyskinesia (involuntary movements) in Parkinson’s disease, and a higher risk of both short- and long-term mortality among people with coronary artery disease. And, a large study of the general population in Belgium (including over 9,000 participants) found that even after adjusting for many other variables (such as age, sex, body mass index, blood lipids, uric acid, smoking status, and more), blood chloride levels were one of the strongest predictors of all-cause mortality, death from cardiovascular disease, and death from non-cardiovascular causes.
That being said, because the body tightly regulates the amount of chloride in the blood, serum chloride concentration isn’t a sensitive marker of chloride intake. So, these associations may reflect (at least in part) other physiological processes in the body involving electrolyte regulation, rather than a problem of not eating enough chloride! This would also explain the discrepancy between chloride seeming to negatively impact cardiovascular and skeletal health when its dietary intake is high, while the opposite is seen with blood levels.
Chloride and Bone Health
Although much more research is needed, it’s also possible that chloride contributes to osteoporosis, and could even be at least partly responsible for the bone-harming effects some studies have attributed to sodium. One small trial found that while sodium chloride increased the urinary excretion of calcium among participants, sodium bicarbonate did not—suggesting the chloride component may be responsible for this effect. Likewise, research has shown that chloride ions play a major role in the biology of osteoclasts (bone-dissolving cells), and that chloride is involved specifically in the bone-resorption activity of these cells (the process of breaking down bone tissue and releasing the minerals it contains). It stands to reason that higher chloride intake would support osteoclast activity and potentially lead to bone loss, especially in the context of a diet low in other bone-supportive nutrients (such as calcium, vitamin D, or vitamin K).
Intriguingly, mutations or disruptions in a specific chloride channel (CIC-7) causes a bone disease called osteopetrosis, in which too much bone mass builds up—essentially the opposite of the more widely-known osteoporosis! This particular chloride channel has even been the target of research for osteoporosis treatments, with scientists hypothesizing that inhibiting these channels would lead to a decrease in bone resorption and increase in bone mass.
Didn’t know chloride was this interesting? Maybe your friends will enjoy this too!
Health Effects of Chloride Deficiency
Due to the widespread use of table salt, chloride deficiency is very rare. However, an insufficiency—especially relative to other electrolytes or to water intake—can lead to disrupted acid-base balance within the body, producing a condition called metabolic alkalosis and causing symptoms like confusion, muscle twitching and spasms, lightheadedness, numbness or tingling in the face or extremities, tremors, fatigue, and irritability. Historically, dietary chloride deficiency syndrome has mostly been observed in infants: for example, in the 1970s, when the baby food industry removed added salt from commercial milk formulas in response to anti-salt recommendations of the time, hundreds of infants began suffering from failure to thrive, muscular weakness, food refusal, constipation, and delayed motor development. Laboratory tests found that the infants had reduced urinary chloride excretion and low blood levels of chloride, and when the infants were fed milk with increased chloride content, their symptoms remitted.
Low blood chloride levels (technically called hypochloremia) are more often caused by non-dietary factors affecting fluid or electrolyte balance—such as diuretic therapy, ongoing vomiting, diarrhea, or water gain that leads to imbalanced chloride concentrations (such as from congestive heart failure or excessive antidiuretic hormone secretion). It’s also possible that increased activity of the sympathetic nervous system and renin-angiotensin-aldosterone system can result in reduced chloride concentrations. Addison’s disease, a condition of adrenal insufficiency (where the adrenal glands aren’t producing enough cortisol and aldosterone), can also cause abnormally high chloride excretion, leading to low levels in the blood.
In the above cases, a chloride blood test can help assess whether chloride levels are in the normal range. This is a blood sample-based lab test commonly ordered as part of an electrolyte panel. Test results revealing low levels (typically below 95 milliequivalents of chloride per liter of blood) can indicate certain conditions like heart failure, lung disease, and adrenal issues. Your healthcare provider will help determine what your results mean, based on your particular health situation!
How Much Chloride Do We Need?
Although establishing a recommended dietary intake for chloride has been difficult (due to few biochemical markers being available to assess chloride intake), most health organizations have set reference values equimolar to those for sodium. The European Commission, for example, states that 3.1 g daily of chloride for adults should be both safe and adequate, and the Food and Nutrition Board at the Institute of Medicine, as well as the nutrition societies of Germany, Austria, and Switzerland, set the adequate intake level for chloride at 2.3 g daily. For most people, consuming a varied diet that doesn’t intentionally exclude salt or sodium should naturally yield enough chloride.
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