The element chlorine itself is a poisonous gas that is soluble in water; in nature and in our body, it exists primarily as the chloride anion, the negatively charged ion that joins with cations such as sodium to make salt (sodium chloride) and with hydrogen to make stomach acid (hydrochloric acid). Chloride makes up about 0.15 percent of our body weight and is found mainly in the extracellular fluid along with sodium. Less than 15 percent of the body chloride is found inside the cells, with the highest amounts within the red blood cells. As one of the mineral electrolytes, chloride works closely with sodium and water to help the distribution of body fluids.
Chloride is easily absorbed from the small intestine. It is eliminated through the kidneys, which can also retain chloride as part of their finely controlled regulation of acid-base balance. Chloride is also found along with sodium in perspiration. Heavy sweating can cause the loss of large amounts of sodium chloride, as well as some potassium.
Chlorine gas is used by many water-treatment plants as an agent to kill microorganisms in the water. It has been a great public health addition for eradicating disease in contaminated areas. But is it overused? Many are concerned with the levels of residual chlorine in drinking water because excess chlorine is thought to combine with certain organic water pollutants to form toxic chemicals and carcinogens (see Chapter 1, Water).
Sources: Chloride is obtained primarily from salt, such as standard table salt or sea salt. It is also contained in most foods, especially the vegetables. Seaweeds (such as dulse and kelp), olives, rye, lettuce, tomatoes, and celery are some examples of good chloride-containing foods. Potassium chloride (KCl) is also found in foods or as the “salt substitute.”
Functions: Chloride travels primarily with sodium and water and helps generate the osmotic pressure of body fluids. It is an important constituent of stomach hydrochloric acid (HCl), the key digestive acid. Chloride is also needed to maintain the body’s acid-base balance. The kidneys excrete or retain chloride mainly as sodium chloride, depending on whether they are trying to increase or decrease body acid levels. Chloride may also be helpful in allowing the liver to clear waste products.
Uses: Chloride is commonly used as sodium chloride, such as in salt tablets, to help replace the sodium and chloride lost in perspiration on hot days or with exercise. Chlorine is used in treating drinking water, swimming pools, hot tubs, and so on to kill bacteria and other microorganisms.
Deficiency and toxicity: Neither problem is very common nor worthy of much concern. Large amounts of chloride intake (more than 15 grams per day), usually in salt, may cause some problems with fluid retention and altered acid-base balance (although the main problem lies with the sodium). Chlorine itself, as gas or liquid, can be very irritating and toxic.
Chloride deficiency can arise from diarrhea, vomiting, or sweating. It can lead to metabolic alkalosis (body fluids becoming too alkaline), low fluid volume, and urinary potassium loss. This can cause further problems in acid-base balance. Infant formulas without chloride can cause some of these problems, which are alleviated when chloride is given.
Requirements: Chloride is so readily available in our normal high-salt food supply that there is no RDA. Infants probably need about 0.5-1 gram daily. The amount increases with age; adults needs are the range of 1.7-5 grams daily, but many people consume much more because of the salt content of their diet.