Chloride is an anion (a negatively charged ion), generally consumed as sodium chloride (NaCl) or table salt. There is a high correlation between the sodium and chloride contents of the diet, and only under unusual circumstances do levels of sodium and chloride vary in the diet independently. Adequate intake of sodium chloride is required for maintenance of extracellular fluid volume. Chloride is both actively and passively absorbed. Urine excretion reflects chloride intake, with low or no chloride found in deficiency states.
In general chloride has received little attention in dietary assessment and has been omitted from food composition tables. However, chloride content of infant cow’s milk and soy formulae has stimulated interest in the past 15 years because of iatrogenic hypochloremia induced by several infant formulas with deficient chloride concentrations.
Deficiencies
An adequate intake of sodium chloride to sustain losses may result in hypotension (abnormally low arterial blood pressure). Depending on intake of “free” water, hyponatremia (deficiency of sodium in the blood) and hypochloremia may ensue, such as in water overload, wasting, and trauma with sequestration of extracellular fluid as in burns. Selective chloride deficiency (without sodium deficiency) may result from vomiting, as in pyloric stenosis in infancy or continuous gastric suction with resulting metabolic alkalosis. A familial autosomal recessive condition with chronic diarrhea and defective chloride reabsorption (Barter’s Syndrome) also causes hypochloremia. Renal tubular disorders, cystic fibrosis with excessive sweating and loss of chloride in the perspiration and diuretic use may also cause low chloride states. As mentioned above, inadvertent feeding of chloride deficient infant formulae (<5 mEq Cl/L) resulted in 141 infants in the first year of life developing failure-to-thrive, anorexia, weakness and some ambiguous findings of slow development. Deficiency of chloride alone leads to contraction of extracellular fluid volume and metabolic alkalosis which, in turn, leads to a deficiency of potassium by increasing urinary excretion of potassium.
Diet recommendations
High sodium, low chloride diets should be avoided. In the absence of sodium chloride losing disorders (e.g., excessive sweating, cystic fibrosis, Addison’s disease) several health agencies have recommended that the general population not consume more than 6 g NaCl/day. This recommendation may be of benefit in decreasing cardiovascular morbidity and mortality associated with higher levels of blood pressure in the resting stat. The minimal daily requirement for sodium chloride for normal individuals is less than 2 g NaCl/day. For chloride alone, the Estimated Minimum Requirements per day set by the Food and Nutrition Board are as follows: infants: 0-6 months, 180 mg; 6 months-11 months, 300 mg; 1 year, 350 mg; 2-5 years, 500 mg; 6-9 years, 600 mg; and adolescents and adults, 750 mg.
Food sources
With few exceptions (e.g., monosodium glutamate and sodium bicarbonate) sodium and chloride are most often consumed as sodium chloride (salt). Human milk contains about 420 mg/L and infant formula is now required to contain 55-65 mg/100 kcal and is not to exceed 150 mg/100 Kcal. Undiluted cow’s milk contains about 900-1020 mg/L. Infant formula contains 10.6-13.5 mEq/L and formula for older infants (follow-up formula), 14-19.2 mEq/L. Recommended intakes are 2-4 mEq/L/Kg for infants and children and 60-150 mEq (total) adolescents.
Recent research
The potential of sodium chloride to increase blood pressure is dependent on concomitant high dietary intake of both sodium and chloride. Blood pressure is not increased by selective sodium (without chloride) loading.