| 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 clear whether 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 conducted. 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, hypertension. 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 and treating 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 to eating. 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. |