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The minerals (inorganic nutrients) that are relevant to human nutrition include water, sodium, potassium, chloride, calcium, phosphate, sulfate, magnesium, iron, copper, zinc, manganese, iodine, selenium, and molybdenum. Cobalt is a required mineral for human health, but it is supplied by vitamin B12. Cobalt appears to have no other function, aside from being part of this vitamin. There is some evidence that chromium, boron, and other inorganic elements play some part in human nutrition, but the evidence is indirect and not yet convincing. Fluoride seems not to be required for human life, but its presence in the diet contributes to long term dental health. Some of the minerals do not occur as single atoms, but occur as molecules. These include water, phosphate, sulfate, and selenite (a form of selenium). Sulfate contains an atom of sulfur. We do not need to eat sulfate, since the body can acquire all the sulfate it needs from protein.
The statement that various minerals, or inorganic nutrients, are required for life means that their continued supply in the diet is needed for growth, maintenance of body weight in adulthood, and for reproduction. The amount of each mineral that is needed to support growth during infancy and childhood, to maintain body weight and health, and to facilitate pregnancy and lactation, are listed in a table called the Recommended Dietary Allowances (RDA). This table was compiled by the Food and Nutrition Board, a committee that serves the United States government. All of the values listed in the RDA indicate the daily amounts that are expected to maintain health throughout most of the general population. The actual levels of each inorganic nutrient required by any given individual is likely to be less than that stated by the RDA. The RDAs are all based on studies that provided the exact, minimal requirement of each mineral needed to maintain health. However, the RDA values are actually greater than the minimal requirement, as determined by studies on small groups of healthy human subjects, in order to accomodate the variability expected among the general population.
The RDAs for adult males are 800 mg of calcium, 800 mg of phosphorus, 350 mg of magnesium, 10 mg of iron, 15 mg of zinc, 0.15 mg of iodine, and 0.07 mg of selenium. The RDA for sodium is expressed as a range (0.5-2.4 g/day). The minimal requirement for chloride is about 0.75 g/day, and the minimal requirement for potassium is 1.6-2.0 g/day, though RDA values have not been set for these nutrients. The RDAs for several other minerals has not been determined, and here the estimated safe and adequate daily dietary intake has been listed by the Food and Nutrition Board. These values are listed for copper (1.5-3.0 mg), manganese (2-5 mg), fluoride (1.5-4.0 mg), molybdenum (0.075-0.25 mg), and chromium (0.05-0.2 mg). In noting the appearance of chromium in this list, one should note that the function of chromium is essentially unknown, and evidence for its necessity exists only for animals, and not for human beings. In considering the amount of any mineral used for treating mineral deficiency, one should compare the recommended level with the RDA for that mineral. Treatment at a level that is one tenth of the RDA might not be expected to be adequate, while treatment at levels ranging from 10-1,000 times the RDA might be expected to exert a toxic effect, depending on the mineral. In this way, one can judge whether any claim of action, for a specific mineral treatment, is likely to be adequate or appropriate.
People are treated with minerals for several reasons. The primary reason is to relieve a mineral deficiency, when a deficiency has been detected. Chemical tests suitable for the detection of all mineral deficiencies are available. The diagnosis of the deficiency is often aided by tests that do not involve chemical reactions, such as the hematocrit test for the red blood cell content in blood for iron deficiency, the visual examination of the neck for iodine deficiency, or the examination of bones by densitometry for calcium deficiency. Mineral treatment is conducted after a test and diagnosis for iron-deficiency anemia, in the case of iron, and after a test and diagnosis for hypomagnesemia, in the case of magnesium, to give two examples.
A second general reason for mineral treatment is to prevent the development of a possible or expected deficiency. Here, minerals are administered when tests for possible mineral deficiency are not given. Examples include the practice of giving young infants iron supplements, and of the food industry's practice of supplementing infant formulas with iron. The purpose here is to reduce the risk for iron deficiency anemia. Another example is the practice of many women of taking calcium supplements, with the hope of reducing the risk of osteoporosis.
Most minerals are commercially available at supermarkets, drug stores, and specialty stores. There is reason to believe that the purchase and consumption of most of these minerals is beneficial to health for some, but not all, of the minerals. Potassium supplements are useful for reducing blood pressure, in cases of persons with high blood pressure. The effect of potassium varies from person to person. The consumption of calcium supplements is likely to have some effect on reducing the risk for osteoporosis. The consumption of selenium supplements is expected to be of value only for residents of Keshan Province, China, because of the established association of selenium deficiency in this region with "Keshan disease."
During emergency treatment of sodium deficiency (hyponatremia), potassium deficiency (hypokalemia), and calcium deficiency (hypocalcemia) with intravenous injections, extreme caution must be taken to avoid producing toxic levels of each of these minerals (hypernatremia, hyperkalemia, and hypercalcemia), as mineral toxicity can be life-threatening in some instances. The latter three conditions can be life threatening. Selenium is distinguished among most of the nutrients in that dietary intakes at levels only ten times that of the RDA can be toxic. Hence, one must guard against any overdose of selenium. Calcium and zinc supplements, when taken orally, are distinguished among most of the other minerals in that their toxicity is relatively uncommon.
Minerals are used in treatments by three methods, namely, by replacing a poor diet with a diet that supplies the RDA, by consuming oral supplements, or by injections or infusions. Injections are especially useful for infants, for mentally disabled persons, or where the physician wants to be totally sure of compliance. Infusions, as well as injections, are essential for medical emergencies, as during mineral deficiency situations like hyponatremia, hypokalemia, hypocalcemia, and hypomagnesemia. Oral mineral supplements are especially useful for mentally alert persons who otherwise cannot or will not consume food that is a good mineral source, such as meat. For example, a vegetarian who will not consume meat may be encouraged to consume oral supplements of iron, as well as supplements of vitamin B12.
Iron treatment is used for young infants, given as supplements of 7 mg of iron per day to prevent anemia. Iron is also supplied to infants via the food industry's practice of including iron at 12 mg/L in cow milk-based infant formulas, as well as adding powdered iron at levels of 50 mg iron per 100 g dry infant cereal.
Calcium supplements, along with estrogen and calcitonin therapy, are commonly used in the prevention and treatment of osteoporosis. Estrogen and calcitonin are naturally occurring hormones. Bone loss occurs with diets supplying under 400 mg Ca/day. Bone loss can be minimized with the consumption of the RDA for calcium. There is some thought that all postmenopausal women should consume 1,000-1,500 mg of calcium per day. These levels are higher than the RDA. There is some evidence that such supplementation can reduce bone losses in some bones, such as the elbow (ulna), but not in other bones. Calcium absorption by the intestines decreases with aging, especially after the age of 70. The regulatory mechanisms of the intestines that allow absorption of adequate calcium (500 mg Ca/day or less) may be impaired in the elderly. Because of these changes, there is much interest in increasing the RDA for calcium for older women.
Fluoride has been proven to reduce the rate of tooth decay. When fluoride occurs in the diet, it is incorporated into the structure of the teeth, and other bones. The optimal range of fluoride in drinking water is 0.7-1.2 mg/L. This level results in a reduction in the rate of tooth decay by about 50%. The American Dental Association recommends that persons living in areas lacking fluoridated water take fluoride supplements. The recommendation is 0.25 mg F/day from the ages of 0-2 years, 0.5 mg F/day for 2-3 years, and 1.0 mg F/day for ages 3-13 years.
Magnesium is often used to treat a dangerous condition, called eclampsia, that occasionally occurs during pregnancy. In this case, magnesium is used as a drug, and not to relieve a deficiency. High blood pressure is a fairly common disorder during pregnancy, affecting 1-5% of pregnant mothers. Hypertension during pregnancy can result in increased release of protein in the urine. In pregnancy, the combination of hypertension with increased urinary protein is called preeclampsia. Preeclampsia is a concern during pregnancies as it may lead to eclampsia. Eclampsia involves convulsions and possibly death to the mother. Magnesium sulfate is the drug of choice for preventing the convulsions of eclampsia.
Treatment with cobalt, in the form of vitamin B12, is used for relieving the symptoms of pernicious anemia. Pernicious anemia is a relatively common disease which tends to occur in persons older than 40 years. Free cobalt is never used for the treatment of any disease.
Evaluation of a patient's mineral levels requires a blood sample, and the preparation of plasma or serum from the blood sample. An overnight fast is usually recommended as preparation prior to drawing the blood and chemical analysis. The reason for this is that any mineral present in the food consumed at breakfast may artificially boost the plasma mineral content beyond the normal fasting level, and thereby mask a mineral deficiency. In some cases, red blood cells are used for the mineral status assay.
The healthcare provider assesses the patient's response to mineral treatment. A positive response confirms that the diagnosis was correct. Lack of response indicates that the diagnosis was incorrect, that the patient had failed to take the mineral supplement, or that a higher dose of mineral was needed. The response to mineral treatment can be monitored by chemical tests, by an examination of red blood cells or white blood cells, or by physiological tests, depending on the exact mineral deficiency.
There are few risks associated with mineral treatment. In treating emergency cases of hyponatremia, hypokalemia, or hypocalcemia by intravenous injections, there exists a very real risk that giving too much sodium, potassium, or calcium, can result in hypernatremia, hyperkalemia, or hypercalcemia, respectively. Risk for toxicity is rare where treatment is by dietary means. This is because the intestines act as a barrier, and absorption of any mineral supplement is gradual. The gradual passage of any mineral through the intestines, especially when the mineral supplement is taken with food, allows the various organs of the body to acquire the mineral. Gradual passage of the mineral into the bloodstream also allows the kidneys to excrete the mineral in the urine, should levels of the mineral rise to toxic levels in the blood.
Brody, Tom. Nutritional Biochemistry. San Diego: Academic Press, 1998.
mineralsChemical elements required in the diet, usually in small amounts, to maintain health. Apart from iron and calcium, deficiency is comparatively rare. The essential minerals are calcium, iron, magnesium, copper, selenium, phosphorus, fluorine, potassium, sodium and zinc.
mineralsinorganic substances which are obtained in a well-balanced diet. The substances required in the largest amounts (sometimes known as macrominerals) are sodium, potassium, calcium, phosphorus and magnesium, and many others are essential in smaller amounts. Minerals are essential in all metabolic processes, from maintenance of cell volume and structure to muscle contraction and relaxation, regulation of acid-base equilibrium, protection from oxidative stress, bone metabolism, immune function and haemoglobin synthesis. No mineral supplements should be required for athletes who are consuming a well-balanced diet but they frequently take them, especially iron, magnesium and chromium. See Table 1.
|Name and chemical symbol||Reference nutrient intake (adults, per day)||Sources||Functions||Deficiency||Excess|
|Calcium Ca||700 mg||Milk and milk products, green vegetables, soya beans, white bread, hard water||Calcium deposits in soft tissue can occur, but probably not related to high intake|
|Chlorine Cl||3.4 g (as chloride)||Salt-containing foods||Unlikely with normal diet||As NaCl, risk factor for high blood pressure|
|Chromium Cr||25 μg||Vegetables, cereals, meats, vegetable oils, whole grains||Co-factor for some enzymes involved in glucose and energy metabolism|
|Copper Cu||900 μg||Meat, drinking water||Co-factor for some enzymes; intermediate in electron transfer during oxidative phosphorylation||Low activity of antioxidant enzymes||Very high intake can cause liver damage|
|Iodine I||140 μg||Seafood, iodized salt, milk and milk products, meat and eggs||Synthesis of thyroid hormones||Thyroid swelling (goitre) with hypothyroidism: low BMR, lethargy||Rarely any effect; may exacerbate some skin diseases|
|Iron Fe||Liver, kidney, red meat, egg yolk, wholegrains, pulses, dark green vegetables, dried fruit, treacle, cocoa, molasses||Component of haemoglobin, myoglobin and many enzymes||Can be toxic if very excessive. (from blood transfusions rather than from diet); gastrointestinal upset; may promote vascular disease|
|Fluoride F||3-4 mg||Drinking water, mostly as calcium fluoride; tea, seafood||May be important in maintenance of bone structure||Increased risk of tooth decay||Unlikely from dietary sources|
|Magnesium Mg||Cereals, milk, nuts, seeds, and green vegetables||Co-factor for enzymes essential in metabolism; role in calcium homeostasis; skeletal development; neuromuscular function||Uncommon; can occur with malabsorption or in chronic renal failure, when it accompanies hypocalcaemia||Unlikely from dietary sources|
|Phosphorus-P||550 mg (as phosphate)||Milk, cheese, yogurt, meat, poultry, grains, fish||Adenosine phosphate compounds vital in energy metabolism. With Ca in bones and teeth||Only in severe malnutrition; muscle weakness, bone pain, rickets, anorexia, anaemia||In treatment of osteoporosis or bone cancer with biphosphonates|
|Potassium K||3.5 g||Fruit, vegetables, meat, wholegrains||High ECF [K+] (hyperkalaemia) causes cardiac arrest|
|Selenium Se||Seafood, meat, grains, wheat flour||Key component in the endogenous antioxidant, glutathione peroxidase||Health implications of low intake in UK currently under DoH review. May cause abnormality of heart muscle||Excessive supplements: hair loss, skin rash, neurological disorder|
|Sodium Na||1.6 g||Mainly as salt: table salt, and in milk, meat, vegetables, sauces, pickles, processed foods, snacks, cheese||Major extracellular cation; linked to ECF volume, hence to blood volume and blood pressure. Component of bone mineral||Loss in sweat and diarrhoea; dilution in body fluids due to excess water intake. Weakness, cramp; faintness, confusion||Oedema, hypertension|
|Zinc Zn||Red meat, dairy products, eggs, wholegrains, peas, beans, nuts, lentils|