|Sodium is the primary positive ion found in the blood and body fluids; it
is also found in every cell although it is mainly extracellular, working closely with
potassium, the primary intracellular mineral. About 60 percent of body sodium is in the
fluids around cells (extracellular), 10 percent is inside the cells, and around 30 percent
is found in the bones. Sodium is one of the electrolytes, along with potassium and
chloride, and is closely tied in with the movement of water; "where sodium goes,
water goes." Sodium represents about 0.15 percent of the body weight. Approximately
90-100 grams are present in the body, most of which occurs in combination with chloride as
salt, or sodium chloride.
Sodium chloride is present in solution on a large part of the earth's surface in ocean
water. In common usage, the word "salt" refers mainly to sodium chloride, but in
chemistry, a salt is any combination of a positive and a negative ion in crystalline form
or in solution. Sodium chloride is only 75 percent of the salt in seawater, which also
contains potassium chloride (KCl), calcium chloride (CaCl2), and calcium phosphate
(Ca(CPO4)2), as well as other mineral salts.
Sodium, or salt, has been valued throughout history. The word "salt" is the
source of the English word "salary," which originally referred to money paid to
soldiers to buy salt. Yet this value placed on salt has possibly led to its overuse in
industrial society. For millions of years, the human species lived on a natural diet
containing less than 1 gram per day of sodium, and elevated blood pressure was very rare.
Nowadays, 6-12 grams and even higher amounts of salt per day are consumed by people eating
processed and snack foods or as salt added in cooking and preparing foods. Salt itself is
40 percent sodium and 60 percent chloride. Therefore, 5 grams of salt (about one teaspoon)
contain approximately 2 grams of sodium.
High blood pressure is now epidemic in our society as well as in all other cultures eating
high-salt diets. Where natural foods are the only source of sodium, there is almost no
hypertension. These foods contain more potassium, which is found in high amounts in plant
cells as well as in human cells. There is still some controversy about the relationship
between salt and high blood pressure; the sodium-potassium ratio may be even more
important in controlling blood pressure than the actual amount of sodium. Certain people
seem to be more sensitive to sodium and its effects on blood pressure, although it is not
this is due to genetic or other physiologic factors. Restricting sodium may significantly
help the estimated 20-30 percent of the population that is salt sensitive. Reducing salt
intake may have less effect on the blood pressure of other people. In any event, eating a
low-sodium diet on a long-term basis may be one of the best ways to prevent hypertension;
this will likely be even more effective if the diet is low in fat as well. Research
indicates that other minerals, including calcium, magnesium, and chloride, may also be
implicated in high blood pressure.
Sodium, like potassium, is very soluble and, therefore, is easily absorbed from the
stomach and small intestine-nearly 100 percent of the sodium consumed gets into the body.
It goes into the blood and is circulated through the kidneys, which can reabsorb or
eliminate it in order to maintain stable blood sodium levels. About 90 percent of the
sodium consumed in the average diet is in excess of body needs and must be eliminated in
the urine. Therefore, urine levels reflect dietary intake. Aldosterone, a hormone made and
secreted by the adrenal cortex, acts on the kidneys to regulate sodium metabolism.
Some sodium is stored in the bones and is available if needed. Sodium can be lost with
excessive sweating and with vomiting or diarrhea. When this happens, we naturally crave
water and salt. Should we then consume only water, we may experience "water
intoxication," wherein water goes into the cells and causes swelling, which may lead
to symptoms such as headaches, weakness, loss of appetite, or poor memory. More commonly,
though, we first crave salt and then become thirsty for water to dilute or, rather,
balance the osmotic effects of sodium, and help it to be eliminated. This is all carefully
regulated by our masterful kidneys and adrenal glands.
Sources: Almost all foods contain some sodium, particularly as sodium chloride. It is
found in high amounts in all seafood, in beef, and in poultry, and some sodium is in many
vegetables, including celery, beets, carrots, and artichokes. Kelp and other sea
vegetables are fairly high in sodium.
No wholesome natural food has a high salt content. It is only the Westernized diet of
processed foods that has significant salt content, and many people consume these foods as
their primary "diet." In many respects the standard American diet is sad!
Breads, crackers, chips, cheeses, especially the processed types, some peanut butter, and
salt-cured foods such as olives and pickles may constitute a good percentage of a typical
unhealthy diet. Lunch meats and processed or cured meats such as bacon, bologna, corned
beef, and hot dogs are particularly high in salt and other preservatives such as nitrates
and nitrites. Luckily, most people can clear excess sodium chloride from their bodies, but
it creates additional work for the kidneys. After many years, the kidneys may weaken from
this chronic stress and be unable to clear the salt as well, which may lead to more
problems including high blood pressure.
Sodium can also come from nonsalt sources, such as baking soda (sodium bicarbonate),
monosodium glutamate (MSG), sodium propionate, or any other ingredient listed on a package
as soda or sodium "something." Soy sauce, or tamari, has high amounts of sodium
as well, but the sodium is less concentrated than in crystal salt. "Softened"
water also has extra sodium added to replace the naturally occurring magnesium and calcium
that are removed. This is done because the more soluble sodium can wash clothes better and
"bubble" and "soap" more for daily cleaning and bathing, but when this
water is used as a drink, it adds to the already excessive sodium levels.
Functions: Along with potassium, sodium helps to regulate the fluid balance of the body,
both within and outside the cells. Through the kidneys, by buffering the blood with a
balance of all the positive or negative ions present, these two minerals help control the
acid-base balance as well. The high blood levels of sodium contribute to the osmolarity
(concentration of solutes in solution) and thereby regulate the fluid volume of the body
and blood. The shifting of sodium and potassium across the cell membranes helps to create
an electrical potential (charge) that enables muscles to contract and nerve impulses to be
Sodium is also important to hydrochloric acid production in the stomach and is used during
the transport of amino acids from the gut into the blood.
Since sodium is needed to maintain blood fluid volume, excessive sodium can lead to
increased blood volume and elevated blood pressure, especially when the kidneys do not
clear it efficiently. It is easier to prevent hypertension with low salt intake than to
treat it by lowering salt in the diet. Hypertension is more frequent in people who have a
high salt intake, especially in people with low levels of potassium in their diets. Fresh
fruits and vegetables are high in potassium and low in sodium, and research shows that
increased potassium can balance out some of the effects high sodium intake has on blood
pressure. Elderly people and the black population are more prone than others to elevated
blood pressure. In cultures that consume low-sodium diets, there is very little, if any,
Uses: There is not really a physiologic need for added salt or sodium in our diet. Our
bodies tolerate and, in fact, probably do best on a much lower sodium intake than is
provided by the average Westernized diet. So far more problems are caused by excess
sodium-high blood pressure, premenstrual symptoms, and water retention, for example-than
there are low-sodium difficulties that require treatment with sodium. Low sodium levels
can, however, result from habitually avoiding sodium or from hot weather and severe
perspiration; extra salt or sodium can help here. Potassium may also be needed. Preventing
heatstroke and leg cramps are occasional uses for sodium. It is possible that low sodium
levels can cause blurred vision, edema, and even high blood pressure or, on the other
hand, decreased fluid volume and low blood pressure. In these situations, additional
sodium may be helpful. Salt is also employed to preserve foods, protecting them from
oxidation and breakdown from microorganism activity.
Deficiency and toxicity: In the case of sodium, there is more of a concern with toxicity
from excesses than with deficiencies. Some people, as many as 30 percent, are sensitive to
high levels of dietary sodium and develop hypertension from too much salt. However,
hypertension is only one of the problems related to excess sodium; premenstrual problems
may become more severe with too much salt, and toxemia of pregnancy is correlated with
dietary sodium levels.
Consumption of more than 12 grams a day of salt is not uncommon; to limit salt intake to
about 5 grams per day, which provides about 2 grams of sodium. To reduce sodium intake,
eat more potassium-rich fruits and vegetables, and prepare foods without adding salt prior
Sodium deficiency is less common than excess sodium, as this mineral is readily available
in the diet, but when it does occur, as with excessive sweating and sodium losses,
deficiency can cause problems. The body can lose up to 8 grams per day of sodium through
sweat; however, a loss of this amount usually requires about two to three quarts of sweat.
Other causes of sodium deficiency include low intake, diarrhea or vomiting, and general
malnourishment, particularly of carbohydrates. The deficiency is usually accompanied by
water loss. When sodium and water are lost together, the extracellular fluid volume is
depleted, which can cause decreased blood volume, increased hematocrit (blood count),
decreased blood pressure, and muscle cramps. Other symptoms include nausea and vomiting,
dizziness, poor memory and impaired concentration, somnolence, and muscle weakness. More
seriously, circulatory collapse and shock may occur. Debilitating or wasting diseases such
as cancer or tuberculosis may also produce low-sodium states.
When sodium is lost alone, water flows into the cells, causing cellular swelling and
symptoms of water intoxication. These may include anorexia, fatigue, apathy, and muscle
twitching. With low sodium, there is also usually poor carbohydrate metabolism.
When we lose sodium through sweat, the best treatment is not just replacement with salt
tablets but by drinking salt solution prepared by adding about one-fifth teaspoon (1 gram)
of salt to a quart of water; this will replenish us with a concentration similar to that
in perspiration. Most salt tablets contain 1 gram of salt. One tablet can be taken with a
quart of water, or two or three tablets with two or three quarts of water to replace
greater fluid losses. It is ideal to add some potassium as well, about 500 mg. per quart.
Requirements: There is no specific RDA for sodium because almost everyone consumes more
than needed. The Senate Select Committee on Nutrition and Human Needs suggests about 5
grams of salt, which provides about 2 grams of sodium, per day. We really need only about
0.5 gram to maintain the body's salt concentration and probably 1-2 grams to be safe,
unless we perspire a great deal or are active exercisers.
Most people consume excess sodium. The average American diet contains about 3-6 grams of
sodium, or about 7-15 grams of salt, per day. There are tribes that cook their food in
seawater and consume huge amounts of salt, up to 40 grams per day. These people have a
higher incidence of hypertension.
Another way to evaluate salt intake is to break down how it comes into the diet. The
average diet derives about 3-4 grams of naturally occurring salt in food, 4-5 grams from
eating processed foods, and another 3-4 grams from salt added in cooking or at the table.
That adds up to about 10-13 grams of sodium chloride, or approximately 4-5 grams of
sodium, per day, twice the suggested level. Higher sodium intake has evolved in the last
century or two as a result of habit, taste, and social customs. It is probably most
helpful to limit sodium to 1-3 grams per day and to obtain at least as much potassium as
sodium, although the ideal potassium intake is double that of sodium. These precautions
reduce the risk of sodium- sensitive hypertension and other effects of excess sodium.
Potassium chloride as a salt substitute may be one helpful way to maintain this
sodium-potassium balance. Eating more fresh fruits and vegetables is a good safeguard
against problems with high blood pressure or diseases of the cardiovascular system.