Sodium

Description

There are estimated to be approximately 120 grams of sodium in the adult human body. About 33% of total body sodium is found in the skeletal structure. The rest is found in the extracellular fluids of the body as well as in nerve and muscle tissue.

Sodium is essential for the transmission of nerve impulses down nerve fibers and in the contraction of muscle cells. Sodium in both these functions is displaced across biological membranes, thereby forming a temporary charge imbalance or impulse.

Sodium is important in regulating the plasma volume and fluid balances in the body. It is also vital, along with chloride and bicarbonate, to maintaining the body's acid/base balance. It functions in the sodium pump, which plays an important role in maintaining the fluid balance of cells and in transporting glucose across the intestinal cells into the blood.

Method of Action

Sodium is the primary mineral ion found in extracellular fluids. The sodium concentration outside of the body's cells is balanced by the concentration of potassium within the cell. If the concentration of ions on one side of the cell membrane becomes too high, relative to the other side, water will flow from the side of low concentration to the side of high concentration in order to reestablish the concentration balance and equilibrium of both sides. The "sodium pump," which exchanges sodium from within the cell for potassium outside the cell, helps to regulate this mechanism of cellular and extracellular osmotic balance.

Sodium is part of the salt sodium bicarbonate, which acts within the blood to buffer high acid concentrations. Sodium is an important constituent of other buffering compounds, which act to maintain the acid/base balance of the blood plasma and body fluids. In the kidney, sodium from the urine is exchanged for acidic hydrogen ions formed by the epithelial cells. The sodium binds with bicarbonate ions and hence restores the buffering bicarbonate ion to the blood. Sodium is present as a constituent of various inorganic salts found in intestinal juices. It is also present as sodium chloride in the body's red blood cells.

Sodium ions are essential for the transmission of nerve impulses. Stimulation of nerve fibers causes the secretion of acetylcholine from the membrane adjoining two nerve cells. The acetylcholine molecule, in conjunction with calcium, creates pores in the nerve membrane and sodium ions from the exterior portion of the membrane flow inward. This flow of sodium ions acts to transmit an electrical nerve impulse down the nerve cell to the next nerve junction; where the same process occurs after transmission, sodium is returned to the outside of the membrane by the "sodium pump." Sodium impulses of a similar kind are responsible for the transmission of nerve impulse to muscle tissue.

Sodium is absorbed readily in the intestine. Excretion is primarily via urine and is regulated by the hormone aldosterone. Aldosterone is released in response to the liver-produced enzymes angiotensin 1 and 2. These enzymes are in turn secreted upon stimulation of the liver by the enzyme renin, which is produced by the renal cortex upon a decrease in sodium levels within the body. Aldosterone promotes the action of the "sodium pump" in actively pumping sodium from excretory fluids back into the bloodstream.

Antimicrobial agents such as tetracycline, penicillin, and neomycin, and anti-inflammatory agents such as colchicine and salicylazosulfapyridine, tend to impair sodium absorption.

Properties & Uses

Sodium is beneficial in alleviating symptoms of sodium deficiencies such as weakness, muscle cramps, and aches.

Sodium chloride is helpful in the treatment of dehydration due to excessive salt loss and/or inadequate intake and has been used to minimize decreases in blood volumes experienced by fasting patients.

Sodium chloride supplementation is advised for individuals who experience excessive perspiration on a regular basis. Sodium supplements are also used to supply adequate sodium intake for low weight or premature infants, who frequently are subject to excessive urinary excretion.

Restricted salt intake is advised for persons with edema, hypertension, congestive heart failure, or chronic renal failure. All of these conditions can be aggravated by sodium buildups or high sodium concentration in the body.

Consequence of Deficiency

Sodium deficiency may result in a phenomenon labeled "low salt syndrome." This condition is marked by such symptoms as: weakness, laziness, anorexia and vomiting, mental confusion, abdominal cramps, and skeletal muscle aches.

Sodium deficiencies can result in a reduction of plasma volume with concomitant reductions in renal blood flow and blood filteration rate.

Sodium deficiencies can result from: chronic wasting illness (e.g., cancer, liver disease), major surgery or trauma, excessive sweating, or ingestion of various drugs which impair sodium absorption.

Toxicity Factors

Excessive sodium intake has been linked to increased blood pressure in some individuals. It has also been linked to an increased incidence of migraine headaches.

Sodium chloride intakes of 35 to 40 grams daily can result in edema. Links have also been made between high sodium chloride intakes and an increased incidence of stomach cancer and cerebrovascular disease.

Sodium chloride doses in excess of several grams per kilogram of body weight per day can be lethal, due to adverse effects on many bodily functions, including heart muscle function.

Recommended Dietary Allowance

RDA for adults:	1,000 - 3,300 mg
RDA for children 11+:	1,000 - 3,300 mg
RDA for children 7-10:	600 - 1,800 mg
RDA for children 4-6:	450 - 1,350 mg
RDA for children 1-3:	325 - 975 mg
RDA for infants 0.5 - 1:	115 - 350 mg
RDA for infants 0 - 0.5:	115 - 350 mg

The above is 1980 values for RDA.

For over thirty years, Recommended Daily Amounts has existed in the United Kingdom. It has been used to measure the adequacy of an individual's diet. However, in 1991 the Committee on Medical Aspects of Food Policy (COMA) gave forth a whole new set of figures upon the request of the Department of Health's Chief Medical Officer. Reference Nutrient Intake (RNI) is one of these sets collectively known as "Dietary Reference Values." RNI is an amount of a nutrient that is enough for almost every individuals, even someone who has high needs for the nutrient. This level of intake is, therefore, considerably higher than what most people would need. If individuals are consuming the RNI of a nutrient they are most unlikely to be deficient in that nutrient.

Food Sources

Asparagus (canned)	Beef
Bread	Corn (canned)
Cheese	Egg
Frankfurters	Ham
Milk	Peanut butter
Salmon (canned)	Sardines
Sauerkraut	Swiss chard
Tomato juice	Tuna

Abstracts

References

Battarbee, H.D., Meneely, G.R. CRC Crit Rev Toxicol., 1977/78; 5: 355- 376.

Czanarin, Doris, M. 1984. Minerals - Food, Nutrition and Diet Therapy M.V. Krause and L.K. Mahan. W.B. Saunders Co, Phila.

Dahl, L.K. Am J Clin Nutr., 1972; 25: 231-244.

Dahl, L.K. Am J Clin Nutr., 1968; 21: 787-792.

Fregly, M.J. In: Present Knowledge in Nutrition, Fifth Edition. Nutrition Foundation: Washington, D.C., 1984, pp. 439-458.

Goodhart, Robert S. and Maurice E. Shills. Modern Nutrition In Health And Disease. 6th edition. Philadelphia: Lea and Febiger, 1973.

Grollman, A. Am J Cardiol., 1961; 8: 593-602.

Gros, G. Weller, J.M., Hoohler, S.W. Am J Clin Nutr., 1971; 24: 605-608.

Guthrie, Helen A. Introductory Nutrition. 5th edition. St. Louis: C.V. Mosby Co., 1971.

Hegsted, M.D. 1976. Present Knowledge In Nutrition. 4th ed. The Nutrition Foundation Pub., Washington D.C. 605.

Hunt, S.M., J.L. Groff & J.M. Holbrook. 1980. Nutrition: Principles and Clinical Practice John Wileyand Sons, N.Y. 506.

Kirschmann, J.D. Nutrition Almanac: Nutrition Search. McGrew-Hill: New York. 1990.

Krause, M.V. & L.K. Mahan. 1979. Food, Nutrition and Diet Therapy. 6th ed. W.B. Saunders Company, Philadelphia. 963 pp.

Marsh, A.C., Koons, P.C. J Am Diet Assoc., 1983; 83: 24-27.

Meneely, G.R., Ball, C.O.T. Am J Med., 1958; 25: 713-725.

Meneely, G.R., Battarbee, H.D. Am J Cardiol., 1976; 38: 768-785.

Merck Index, no. 4210.

Murray, M.T. & Pizzorno, J.E. Encyclopedia of Natural Medicine. Rocklin, CA: Prima Publishing,1991.

Orten, J.M. & Otto W. Neuhaus. 1982. Human Biochemistry. Mosby Co. St. Louis. 984.

Sanchez-Castillo, C.P., et al. Clin Sci., 1987; 72: 87-94.

Sanchez-Castillo, C.P., et al. Clin Sci., 1987; 72: 95-102.

Walji, H., Vitamin Guide: Essential nutrients for healthy living., Element: Dorset, U.K. 1992.

Walji, H., Vitamin Minerals & Dietary Supplements., Hodder Headline Plc.: London, U.K. 1994.

Williams, Sue Rodwell. Nutrition And Diet Therapy. 5th edition. St Louis: Times Mirror Mosby, 1985.

Wilson, Eva D., et al. Principles Of Nutrition. 4th edition. New York: John Wiley & Sons, 1979.