Archive for March, 2008

Sodium and potassium are unlike other minerals, which are small amounts of inorganic material that participate in the body’s metabolic reactions. Rather, sodium and potassium are considered electrolytes, whose most important function is maintaining proper flow of water inside and outside of body cells. They are part of a delicate balancing mechanism that controls, among other things, blood pressure.

Athletes who lose excessive amounts of sodium through perspiration and people with high blood pressure or those at risk of high blood pressure need to be concerned about maintaining proper electrolyte balance.

FUNCTION

Sodium and potassium exist in and around cells as positively charged particles, known as ions. The water surrounding body cells contains thirty-one times as much sodium as potassium. Inside the cell, the ratio is reversed, with sixteen times as much potassium as sodium. Ions cannot exist in nature. They must be combined with another ion of equal but opposite charge. The most common negatively charged ion paired with both sodium and potassium is chloride. So the most common form of sodium found in nature is sodium chloride (common salt), Potassium also is most often found as potassium chloride.

Together, sodium and potassium provide the electrical potential necessary for cell membranes to be selective as to what they will or will not allow in or out of the cell. The flow of sodium potassium into and out of cells is self-regulated to maintain the proper concentrations of each ion inside the cell. As electrolytes flow across the cell membrane, they carry water with them.

Daily Requirements

It is generally accepted that people need about 1,000 mg of sodium a day, which works out to about 2.5 grams of salt, though most Americans actually eat almost twice as much. Our y potassium requirement is 2,000 to 6,000 mg.

Dietary Sources

We all know of sources of salt in our diet; they are the highly processed foods we like so much, foods such as bacon, canned and instant soup, bouillon, potato chips, pretzels and other snack foods, canned goods, and ham. Additional high-sodium foods are listed in the following table.

Because of the American penchant for salty foods, a typical diet can contain anywhere from 3,000 rng to 7,000 mg of sodium. Low-sodium diets usually provide from 500 to 2,000 mg of sodium. Clearly, as experts have noted, most of us would do well to reduce our salt intake because of the beneficial effect it would have on lowering our blood pressure. This is especially true for people who already have high blood pressure and who are taking medicines to control their pressure, but it also holds true for everyone else.

The fact that the body has a natural balance between sodium and potassium means that you should pay attention to the amount of potassium in your diet. A good way to look at it is that substituting foods with a high potassium content for high-sodium foods will help to reduce the amount of sodium in the fluid outside body cells, lowering blood pressure and improving overall health. Low-sodium diets also help your body to conserve calcium, an important consideration if you are taking extra calcium for osteoporosis.

Food Approximate Sodium Content (MG Per 3 OZ) Approximate Potassium Content (MG Per 3 OZ)

Apples (raw) 0.9 99
Bacon 919 3
Bananas 0.9 333
Beef (dried) 3,870 180
Beef (fresh ground) 42 405
Bread (while) 474 246
Bread (whole wheat) 456 95
Butter 888 21
Cabbage 13 93
Clams 909 180
Green beans (canned) 212 86
Green beans (fresh, cooked) 4 136
Grapefruit 0.9 122
Ham (cooked) 64 292
Margarine 888 21
Milk 45 130
Orange 0.9 180
Peas (fresh, cooked) 0.8 122
Potato 4 453
Raisins 24 687
Sardines (canned) 741 495
Squash 0.9 127
Tomatoes (canned) 117 424
Tomatoes (fresh) 3 366

Raw vegetables provide significant amounts of potassium but their canned versions have lots of added salt and should be avoided. Clams, sardines, and lima beans are rich in sodium but also relatively high in potassium. Some good high-potassium foods are bananas, raisins, potatoes, tomatoes, apples, and oranges. Some other good sources of potassium can be found in the previous table.

Deficiencies

While sodium deficiency can be associated with several diseases, it is found mainly in cases of overexertion, when sodium losses due to perspiration are excessive. Generally, a strenuous workout on the first hot day of the year is more likely to cause sodium depletion than continued exercise, even during hot weather. This is because the body is able to adjust its regulating mechanisms over time to protect itself from adverse conditions. Most people adapt to heat within a few days so that, even though exercise and perspiration may continue, less sodium is lost. Sodium chloride tablets (one or two 1 g tablets for the first few days) or a salt or sport electrolyte solution can be taken to prevent or relieve the condition.

Symptoms of sodium deficiency are muscle and stomach cramps, nausea, and fatigue. Occasionally, pregnant women on sodium-restricted diets develop symptoms of sodium deficiency.

Potassium deficiency usually develops for reasons other than a poor diet. Perhaps the most common reason for concern over potassium intake is the use of diuretic drugs that cause this electrolyte to be lost from the body through the urine. This phenomenon can be controlled to some extent by reducing the amount of sodium in the diet. Normally, the kidneys eliminate large amounts of sodium and some potassium along with water. If there is less sodium to be eliminated, more potassium will be retained.

Another common reason for potassium loss is prolonged diarrhea or vomiting. Fluids in the gut are potassium-rich, and prolonged losses of those fluids call for potassium replenishment. It is also possible, though unusual, to be potassium-deficient because of long-term intravenous therapy with fluids that are potassium-poor.

Symptoms of potassium deficiency include lethargy, poor reflexes, muscle cramps and spasms, weakness and, most important, abnormal heartbeat. If a person already has heart disease, potassium deficiency can make matters worse. Potassium deficiency can also make you more sensitive to digoxin, medicine used to treat heart failure and some abnormal heart rhythms. The symptoms of this problem would be the same as for a digitalis overdose: nausea, vomiting, loss of appetite, abnormal heart rhythms, and heart failure symptoms.

Toxicity

Most health authorities agree that excess sodium increases your risk of high blood pressure. Of course, high blood pressure increases your risk of kidney and heart disease. So while salt is not the sole cause of kidney or heart disease, it is one factor we can control. The practice of salting foods leads to a pattern of increasing the desire for salty foods. This is especially true when salt is added to children’s food. By sparing the salt shaker early in life, we can minimize the desire for salty foods later in life and minimize the potential for high blood pressure and kidney and heart disease.

Salt replacement products are designed lo replace the sodium ion while keeping the sally taste people like. The usual approach taken in formulating a salt replacement is to substitute potassium salts for sodium, but this can produce a metallic taste. Newer products take advantage of a wider variety of replacement ions and do not seek to totally eliminate sodium from the product. This yields a better-tasting salt replacement product.

Excess potassium could accumulate if you ate more than 18g a day, but this is highly unlikely. Potassium toxicity usually develops in people who take a potassium supplement (usually prescribed for people taking a diuretic drug) incorrectly. Potassium toxicity can also occur in people with kidney failure. Symptoms of potassium toxicity are similar to those of potassium deficiency: muscle weakness, pain, abnormal heartbeat, and even heart failure. Intravenous calcium (as calcium gluconate) or Kayexelate resin can be prescribed to fight potassium toxicity.

THERAPEUTIC USES

There is little reason for people to take either potassium or sodium, but they may be needed to counteract a deficiency symptom of either of these electrolytes or in situations where potassium or sodium replacement is medically necessary.

Availability

Salt tablets (I g each) may be purchased without a prescription. A great many potassium products are available by prescription. Some potassium replacement products can be purchased as food supplements, but neither sodium nor potassium supplements should be taken without your doctor’s knowledge. Potassium tablets have caused damage to the stomach or intestine. This risk can be minimized by taking a timed-release potassium product.

Vitamin A is a fat-soluble vitamin with four major functions in the body: (1) It helps cells reproduce normally-a process called differentiation (cells that have not properly differentiated are more likely to undergo pre-cancerous changes). (2) It is required for vision; vitamin A maintains healthy cells in various structures of the eye and is required for the transduction of light into nerve signals in the retina. (3) It is required for normal growth and development of the embryo and fetus, influencing genes that determine the sequential development of organs in embryonic development. (4) It may be required for normal reproductive function, with influences on the function and development of sperm, ovaries and placenta.

Where is it found?

Liver, dairy products, and cod liver oil are good sources of vitamin A. Vitamin A is also available in supplement form.

Deficiency Symptoms

Who is likely to be deficient?

People who limit their consumption of liver, dairy foods, and beta-carotene-containing vegetables can develop a vitamin A deficiency. Extremely low birth weight babies (2.2 pounds or less) are at high risk of being born with a deficiency, and vitamin A shots given to these infants have been reported in double-blind research to reduce the risk of lung disease. The earliest deficiency sign is poor night vision. Deficiency symptoms can also include dry skin, increased risk of infections, and metaplasia (a precancerous condition). Severe deficiencies causing blindness are extremely rare in Western societies.

Less severe deficiencies are more likely to occur with a variety of conditions causing malabsorption. A high incidence of vitamin A deficiency in people infected with HIV has also been reported. People with hypothyroidism have an impaired ability to convert beta-carotene to vitamin A. For this reason, some doctors suggest taking supplemental vitamin A (perhaps 5,000-10,000 IU per day) if they are not consuming adequate amounts in their diet.

Very old people with type 2 diabetes have shown a significant age-related decline in blood levels of vitamin A, irrespective of their dietary intake.

Dosage

How much is usually taken?

For most people, up to 25,000 IU (7,500 mcg) of vitamin A per day is considered safe. However, people over age 65 and those with liver disease should probably not supplement with more than 15,000 IU per day, unless supervised by a doctor. In women who could become pregnant, the maximum safe intake is being re-evaluated. However, less than 10,000 IU (3,000 mcg) per day is generally accepted as safe. There is concern that larger intakes could cause birth defects. Whether the average person would benefit from vitamin A supplementation remains unclear.

Side Effects

Are there any side effects or interactions?

Since a 1995 report from the New England Journal of Medicine, women who are or could become pregnant have been told by doctors to take less than 10,000 IU (3,000 mcg) per day of vitamin A to avoid the risk of birth defect. A recent report studied several hundred women exposed to 10,000-300,000 IU (median exposure of 50,000 IU) per day. Three major malformations occurred in this study, but all could have happened in the absence of vitamin A supplementation. Surprisingly, no congenital malformations happened in any of the 120 infants exposed to maternal intakes of vitamin A that exceeded 50,000 IU per day. In fact, the high-exposure group had a 50% decreased risk for malformations compared with infants not exposed to vitamin A. The authors noted that some previous studies found no link between vitamin A and birth defects, and argued the studies that did find such a link suffered from various weaknesses. A closer look at the recent study reveals a 32% higher than expected risk of birth defects in infants exposed to 10,000-40,000 IU of vitamin A per day, but paradoxically a 37% decreased risk for those exposed to even higher levels. This suggests that both “higher” and “lower” risks may have been due to chance.

Excessive dietary intake of vitamin A has been associated with birth defects in humans in fewer than 20 reported cases over the past 30 years. Presently, the level at which vitamin A supplementation may cause birth defects is not known, though combined human and animal data suggest that 30,000 IU per day should be considered safe. Women who are or who could become pregnant should consult with a doctor before supplementing with more than 10,000 IU per day.

Vitamin A supplements can both help and hurt children. Many people have heard that vitamin A supplements support immune function and prevent infections. This is true under some circumstances. However, vitamin A can also increase the risk of infections, according to the findings of a double-blind trial. In a study of African children between six months and five years old, a 44% reduction in the risk of severe diarrhea was seen in those children given four 100,000-200,000 IU applications of vitamin A (the lower amount for those less than a year old) during an eight-month period. On further investigation, the researchers discovered that the reduction in diarrhea occurred only in children who were very malnourished. For children who were not starving, vitamin A supplementation actually increased the risk of diarrhea compared with the placebo group. The vitamin A-supplemented children also had a 67% increased risk of coughing and rapid breathing, signs of further lung infection, although this problem did not appear in children infected with AIDS. These findings should be of concern to American parents, whose children are not usually infected with AIDS or severely malnourished. Such relatively healthy children fared poorly in the African trial in terms of both the risk of diarrhea and the risk of continued lung problems. Vitamin A provided no benefit to the well-nourished kids. Therefore, it makes sense to not give vitamin A supplements to children unless there is a special reason to do so, such as the presence of a condition causing malabsorption (e.g., celiac disease).

In a study of people with retinitis pigmentosa (a degenerative condition of the eye), participants received 15,000 IU of vitamin A per day for 12 years with no signs of adverse effects or toxicity.11 For other adults, intake above 25,000 IU (7,500 mcg) per day can-in rare cases-cause headaches, dry skin, hair loss, fatigue, bone problems, and liver damage. At higher levels (for example 100,000 IU per day) these problems become more common.

A controlled clinical trial showed that people who took 25,000 IU of vitamin A per day for a median of 3.8 years had an 11% increase in triglycerides, a 3% increase in total cholesterol and a 1% decrease in HDL cholesterol compared to those who did not take vitamin A. Although the significance of these findings is not clear, people at risk for cardiovascular disease should use caution when considering long-term vitamin A supplementation.

One study found that increasing the intake of vitamin A in the diet was associated with bone loss and risk of hip fracture, possibly due to a vitamin A-induced stimulation of cells that break down bone. In this study, a vitamin A intake greater than 5,000 IU per day, when compared to a lower intake, was associated with a reduction in bone mineral density that approximately doubles the risk of hip fracture. Beta-carotene (which can be used by the body to make vitamin A) has not been linked to reduced bone mass. Until more is known, people concerned about osteoporosis may consider taking beta-carotene supplements rather than supplementing with vitamin A.

Data from test tube, animal, and human studies show that excessive vitamin A intake can accelerate bone loss and inhibit formation of new bone, increasing the risk of osteoporosis. In humans, small studies have found these effects at about 85,000-125,000 IU per day.

Taking vitamin A and iron together helps overcome iron deficiency more effectively than iron supplementation alone. Supplementation with zinc, iron, or the combination has been found to improve vitamin A status among children at high risk for deficiency of the three nutrients.

Very little is known about the role of several trace minerals in human nutrition, but animal research has revealed a possible role for some of them. As of this writing, there is no reason to supplement any of these minerals on a regular basis.

Cadmium stimulates many enzyme systems, but none of them rely on cadmium alone: they are also stimulated by other minerals. Cadmium toxicity has been reported in industrial workers exposed to cadmium dust. They developed a disease called itai-itai, which causes breathing difficulties.

Cobalt has been identified with human deficiency symptoms. The deficiency symptoms are related to its role as a component of vitamin B12. Cobalt toxicity can lead to thyroid overgrowth in infants.

Nickel may interact with iron, but its exact function is not known.

Silicon may play a role in the function of our connective tissue. This is where it is most common in the body, but its exact role is not known.

Vanadium is thought to play a role in the metabolism of our bones and teeth. Many claims have been made for vanadium, but none have been proven.

The functions of tin and arsenic in human nutrition are not known.

What is the most important information I should know about vitamin A?

Do not take more vitamin A than is prescribed for you or than is recommended on the package. Too much vitamin A can be dangerous.

What is vitamin A?

Vitamin A is found in food from animal sources and it is also produced synthetically. Vitamin A is important for the eyes and skin, and for normal growth.

Vitamin A is used to treat vitamin A deficiency.

Who should not take vitamin A?

Before taking vitamin A, talk to your doctor, pharmacist, or health care professional if you have any other medical conditions, allergies, or if you take other medicines or other herbal/health supplements.

Do not take a vitamin A supplement without first talking to your doctor if you are pregnant.

Although some vitamin A is necessary for the normal development of a baby, doses in excess of the U.S. recommended dietary allowance (RDA) of 5,000 USP units per day may cause birth defects.

Do not take a vitamin A supplement without first talking to your doctor if you are breast-feeding a baby.

How should I take vitamin A?

Take vitamin A exactly as directed by your doctor or as directed on the package. If you do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.

Take each dose with a full glass of water.

Measure the liquid forms of vitamin A with the dropper provided.

Do not take more vitamin A than is prescribed for you or than is recommended on the package.

Too much vitamin A can be dangerous.

Store vitamin A at room temperature away from light, moisture, and heat.

What happens if I miss a dose?

Take the missed dose as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and take only the next regularly scheduled dose. Do not take a double dose of vitamin A.

What happens if I overdose?

Seek emergency medical attention.

Symptoms of a vitamin A overdose include tiredness, discomfort, lethargy, upset stomach, decreased appetite, vomiting, slow or decreased growth, joint soreness, irritability, headache, drying and cracking of the lips and skin, hair loss, and yellowing of the skin.

What should I avoid while taking vitamin A?

Avoid prolonged use of mineral oil while taking vitamin A.

There are no other restrictions on food, beverages, or activities while you are taking vitamin A unless otherwise directed by your health care provider.

What are the possible side effects of vitamin A?

Stop taking vitamin A and seek emergency medical attention if you experience an allergic reaction (difficulty breathing; closing of your throat; swelling of your lips, tongue, or face; or hives).

Other, less serious side effects may occur with large doses or prolonged use of vitamin A. Notify your doctor if you experience

tiredness;
nausea, vomiting, or decreased appetite;
irritability;
headache;
dryness or cracking of the lips or skin; or
hair loss.

Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

What other drugs will affect vitamin A?

Before taking vitamin A, tell your doctor if you are taking any of the following medicines:

oral birth control pills,
cholestyramine (Questran), or
mineral oil.

You may not be able to take vitamin A, or you may require a dosage adjustment or special monitoring during your treatment if you are taking any of the medicines listed above.

Drugs other than those listed here may also interact with vitamin A. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines or herbal/health supplements.

Where can I get more information?

Your doctor, pharmacist, or health care provider may have more information about vitamin A.

Selenium may be very important in human nutrition because mineral may aid in preventing some cancers.

Function

Selenium is a component of one form of an important enzyme called glutathione peroxidase. This enzyme exists in fluid in and around all body cells and it inactivates substances called peroxides, which contain high levels of oxygen. Since excess oxygen can be toxic to body cells and cause tissue destruction, peroxides pose a threat to vital tissues and membranes, causing cancer or even death.

Glutathione peroxidase is thought to be our first line of defense against peroxidase damage. Vitamin E, located inside cell membranes, is a second line of defense against peroxide. Thus, selenium and vitamin E go hand in hand in their protective role for body tissues.

Dietary Sources

Human selenium requirements are not known with certainty. An estimated safe and adequate daily selenium intake is between 50 and 200 mcg. Since our daily requirement is not known and many vitamin/mineral supplements do not contain selenium, we are faced with a difficult challenge when it comes to choosing a selenium supplement. Because of possible toxicity concerns, you should keep your daily intake below 100 mcg. This, together with the selenium in your food, should be ample.

Dietary Sources

The selenium content of food is highly variable because of the wide variability in selenium concentrations in the soil in which foods are grown. Seafood, organ meats, and whole grains are considered to be good sources of selenium. Fruits and vegetables are considered to be selenium-poor. Food-refining processes, cooking, and discarding the water in which foods are cooked all contribute to our difficulty in getting enough selenium in our diet.

Dietary surveys indicate that daily average intake varies from 50 to150 mcg a day.

DEFICIENCIES

Selenium deficiency has been well documented and studied in livestock and lab animals. Animal deficiencies cause a variety of serious and life-threatening conditions, including infertility, muscular dystrophy, exudative diathesis in fowl, pancreatic fibrosis in chicks, hepatosis in pigs, and unthriftiness or sickliness in cattle and sheep. These deficient states are much the same as those associated with vitamin E deficiency, and large doses of selenium will cure most, but not all, vitamin E deficiency symptoms. Since both selenium and vitamin E play a role in protecting against oxidative damage, it is not surprising that one can sometimes be substituted for the other.

Human selenium deficiency is almost unknown, even in areas of the country where livestock suffer selenium deficiency. Selenium deficiency has, however, been seen in a few people with alcoholic cirrhosis and a few people receiving long-term intravenous feeding without added selenium. They suffered from heart problems that responded to selenium supplements. There is also speculation that Keshan’s disease, a fatal heart disease seen in children living in certain sections of China, may be related to selenium deficiency.

TOXICITY

Selenium toxicity in animals can lead to blindness, excess salivation, paralysis, and difficulty breathing. Interestingly, human selenium poisoning has not been reported to come from foods grown in the same areas where livestock are being poisoned by selenium. Selenium poisoning has, however, been reported in several Chinese villages where drought forced villagers to eat vegetables high in selenium. In these villages, daily intakes were found to be 3,000 to 7.000 mcg a day. Villagers suffered hair and nail loss and nervous system problems.

Epidemiological studies have also demonstrated a relationship between high selenium concentrations in water and dental cavities.

Therapeutic Uses

Animal studies have conclusively demonstrated that selenium deficiencies increase the number and growth rate of tumors when cancer-causing chemicals are administered. High selenium intake seems to exert a protective effect in these studies. Since the selenium-dependent enzyme glutathione peroxidase protects against cellular peroxidase damage, as discussed under “Function,” it seems reasonable to assume peroxidase damage is somehow related to cancer.

The only evidence that selenium may protect against tumors in man is obtained from broad-based epidemiological studies. If one compares the selenium content of drinking water with cancer death rates in various parts of the country, or even between countries, one finds the following relationship: Higher selenium levels are associated with a lower cancer rate. Other factors obviously enter into this and cancer is still a problem in high-selenium areas. It has been estimated that the risk for some cancers is twice as high in low-selenium areas than in high-selenium areas. High selenium concentrations can be found in parts of Wyoming, Alaska, Arkansas, Mississippi, South Dakota, and Colorado. Low selenium concentrations can be found in California, Ohio, Washington, Oregon, Pennsylvania, Indiana, and New York. Breast, colon, and lung cancers, our biggest killers, seem to be affected by selenium intake.

Zinc, cadmium, and copper counteract the effects of selenium in the body, and high intakes of these minerals may even counter the cancer-protective effects of selenium, though there no human studies to support this claim. We believe it is better to take a mineral mixture balanced by Mother Nature—that is, the kind found in whole grains and seafood—than to fool with potent mineral supplements, at least until more is known.

The association of selenium deficiency with heart problems in humans has created interest in the therapeutic benefit of selenium supplements in heart disease. The answer to this proposition is not yet in.

SUBSTANTIATED CLAIMS

Selenium, like manganese, has been erroneously promoted for an antiaging effect because of its role in controlling oxygen levels. Other unsubstantiated claims include detoxifying heavy metals, drugs, alcohol, and cigarette smoke; improving skin problems; increasing male potency and sex drive; and arthritis treatment.

AVAILABILFTY

Some vitamin/mineral supplement formulas contain selenium and it is also available in tablet form.