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Sodium — February 2003
2.4 Food
Foods and beverages are the largest sources of sodium intake for humans. Of the sodium present
in foods, a relatively low amount (10%) occurs naturally (Sanchez-Castillo et al. 1987a,b). The
majority of dietary sodium comes from sodium chloride added to food during food processing
and preparation. For example, Sanchez-Castillo et al. (1987a,b) estimated that 15% of dietary
sodium comes from salt added during cooking and at the table, and 75% comes from salt added
during processing and manufacturing. The first National Health and Nutrition Examination
Survey (Abraham and Carroll 1981) reported that approximately 32% of the sodium chloride
consumed came from baked goods and cereals, 21% came from meats, and 14% from dairy
products. Similar results were reported for the FDA Total Diet Study (Pennington et al. 1984).
Using data from the 1989 to 1991 Continuing Survey of Food Intake by Individuals, Subar et al.
(1998) found that 23.4% of the salt in the diet came from a group of foods that included cold cuts
and other processed meats, condiments, snack-type foods (e.g., chips and popcorn), and table
salt; 10.9% from yeast bread; 5.6% from cheese; and 4.1% from ham. These foods contributed
44.1% of the total dietary sodium.
Reported dietary sodium intakes range from 1,800 mg/day to 5,000 mg/day in various studies,
depending on the methods of assessment and whether discretionary sodium use is assessed
(Abraham and Carroll 1981, Pennington et al. 1984, Karanja et al. 1999). Discretionary sodium
intake is highly variable and can be quite large. In a 28-day study, Mickelson et al. (1977) found
that males added an average of about 5,500 mg of sodium chloride (2,200 mg of sodium) to their
food per day. The Food and Drug Administration has found that most American adults tend to
consume between 4,000 and 6,000 mg of sodium per day, whereas individuals on sodium-
restricted diets usually ingest less than 1,000 to 3,000 mg/day (Kurtzweil 1995).
3.0 CHEMICAL AND PHYSICAL PROPERTIES
Sodium (Na) is the most abundant element of the alkali metal group. Elemental sodium has an
atomic weight of 22.99 and is a soft, bright silvery metal. Pure metallic sodium is highly reactive
and burns in air to form sodium oxide, which in turn readily hydrolyzes in water to form sodium
hydroxide. Because elemental sodium is so highly reactive, it is not found freely in nature.
Rather, sodium is found in nature only as the sodium ion (Na
+
) combined with a variety of anions
to form a number of different salts. Common sodium salts are chloride, carbonate, hypochlorite,
and silicate. The physical and chemical properties of five sodium salts are presented in Table
3–1 (Sax 1975, Clayton and Clayton 1981, Sittig 1981, Sax and Lewis 1987, Budavari 1996,
HSDB 2000).
4.0 TOXICOKINETICS
Sodium ions are a normal and essential component of the human body, playing a key role in
controlling and maintaining the proper osmolarity (concentration) and volume of extracellular
body fluids. Both the body content of sodium and its concentration in body fluids are under
homeostatic control. In addition to its role in regulating osmolarity and extracellular fluid
volume, sodium is important in the regulation of acid-base balance and the membrane potential
of cells. As a consequence of these vital functions, the absorption, distribution, and excretion of