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.