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Vitamins, Minerals
and the RDA


Minerals and the RDA
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Minerals are inorganic substances derived from soil and water and incorporated into our diet. Those that are required in large amounts in the diet are called macro-minerals and include calcium, magnesium, and phosphorus. The Recommended Dietary Allowances for calcium and phosphorus in adults are between 800 and 1200 mg per day. Magnesium requirements range between 270 and 400 mg per day in adults. Magnesium and phosphorus are found in all plant and animal foods since they are both major intracellular ions. Deficiency is rare except in malnourished alcoholics. Calcium supplementation is required in many women who fail to ingest adequate calcium in their diet.

There are also a number of trace minerals which serve critical roles in body metabolism but are required in much smaller amounts. These trace minerals and their roles include:

Iron is needed for red cell formation and is also a pro-oxidant used in catalase and other peroxidase-type enzymes. The use of oral iron cannot lead to overload but parenteral iron can be toxic. Iron is commonly deficient in menstruating females, and should be replaced when anemia is identified, or as a preventive in individuals with low range hematocrits. The Recommended Dietary Allowance for iron is between 10 and 15 mg per day.

This is a structural component of enzymes including glutathione peroxidase and type I iodothyronine monodeiodinase. The Recommended Dietary Allowance is between 40 and 70 micrograms per day in adults.

Zinc is an essential component of many different enzymes and is necessary for a variety of metabolic processes. Zinc deficiency was first observed in adolescent boys in Egypt who were eating unleavened whole grain bread containing phytate which bound to zinc in the intestinal tract preventing its absorption. The boys demonstrated growth retardation and delayed puberty. Zinc supplements have been marketed as a cure for impotence without any substantiation of that claim. The daily requirements are comparable to those for iron and range between 12 and 15 mg per day in adults. The major sites of potential losses are in semen and from the gastrointestinal tract with severe diarrhea or fistula. Zinc should not be administered in the absence of any copper and should not be consumed as a separate supplement except in individuals with a demonstrated zinc deficiency.

The elevation of serum copper seen in Wilson's Disease is due to a deficiency of ceruloplasmin, the copper-binding protein. This leads to a syndrome of hepatolenticular degeneration. As mentioned above a copper deficiency can be induced with megadoses of zinc. There is no Recommended Dietary Allowance for copper but an Estimated Safe and Adequate Dietary Daily Intake of 3 mg per day in adults was issued by the National Research Council of the National Academy of Sciences in 1980.

The only major role of iodine is to serve as an essential part of the basic structure of thyroid hormones. Iodine deficiency in areas away from sea water (e.g. highlands around Mexico City, inland areas of Southeast Asia) can lead to goiter formation. Since the late 1950's iodine has been used as a bleaching agent for white flour and iodine deficiency in this country is rare. It is not unusual for individuals immigrating to the U.S. to develop thyroid disease due to the increase in dietary iodine compared to their country of origin. Iodine supplementation in areas that are normally iodine deficient has led to an increase in various types of thyroid diseases including Grave's Disease, Hashimoto's Thyroiditis, and thyroid nodules. It is possible for susceptible individuals to develop thyroid nodules after taking kelp tablets which are rich in iodine.

Chromium is also called glucose tolerance factor, but its effectiveness in enhancing glucose tolerance is unproven. A recent study demonstrated enhanced lifespan in small number of rats given chromium picolinate. The increased interest in this trace mineral based on this small study is probably not justified. A natural source of chromium is brewer's yeast. There is no evidence that it enhances muscle building or fat loss in humans. There is no Recommended Dietary Allowance for humans.

Many other trace minerals including arsenic, cobalt, manganese, molybdenum, nickel, silicon, tin, and vanadium have a variety of metabolic functions. Some of these are not yet well understood. Fortunately, most foods in a varied diet will provide adequate amounts of these trace minerals without the necessity for supplementation. In fact, supplementation in the absence of additional knowledge may be dangerous. For example, in trace amounts arsenic is a required trace mineral, but it is a well-known poison at higher doses.


Nutritional Adequacy
Despite the epidemic of overnutrition in the United States today, there are still some groups at risk for nutritional deficiencies. These groups include: 1) pregnant women 2) the elderly, 3) individuals who smoke, drink excess amounts of alcohol, or abuse drugs. The laboratory assessment of possible deficiencies in these groups is summarized in Table 2.

Nutritional Optimization - Future Directions
While classical vitamin deficiency diseases are rare today in the U.S. except in certain high risk groups (e.g. alcoholics, pregnant teenagers, institutionalized elderly), there are a variety of individuals whose dietary intake is inadequate to maintain optimal health. For instance, it is recommended that Americans eat 25 grams of fiber per day, but the average intake is only about 10 grams. In California, only about one in five people consumes five servings a day of fruits and vegetables as recommended by the US Department of Agriculture. As a result there are a number of micronutrient vitamins and minerals which are deficient but not at levels that would cause disease. Examples include: carotenoids, vitamin E, vitamin C, folate, and selenium. While it is established what nutrient levels constitute deficiency, there is little information on what is suboptimal or what types of responses can be expected following nutritional intervention. It is also unclear why there are individual variations in the absorption of a beta-carotene oral load, the effects of dietary fiber eaten at the same time, or the effects of various fats in the diet on absorption.

Many of the micronutrients contribute to antioxidant effects. For the measurement of the host response to oxidant stress, there are a number of markers including: the measurement of lipid oxidation products such as malondialdehyde or thiobarbituric acid reactive substances (TBARS) in blood or urine; modified DNA bases and/or DNA adducts in peripheral blood cells or urine; vitamin E or vitamin C levels in blood fractions; catalase or superoxide dismutase levels in blood fractions; lipid peroxides in blood; volatile gases such as ethane and pentane in expired breath; total peroxyl radical trapping antioxidant power of serum (TRAP assay); autoxidative (non-cyclooxygenase-derived) eicosanoids in plasma; and the in vitro oxidation of blood fractions such as LDL. The usefulness of such measurements in assessing and managing micronutrient deficiencies is not yet clear. Elevated oxidative stress is found in a number of disease states. For example, hospitalized patients with myocardial infarction have higher oxidative stress than hospitalized controls. Hydrogen peroxide is increased in expired breath from patients with adult respiratory distress syndrome. Micronutrient nutrition also has implications for the prevention and treatment of cardiovascular diseases where oxidized forms of LDL are implicated in the cellular basis for atherosclerosis. It is likely that the amounts of antioxidants that can be derived from the diet and/or supplements will be potent in reducing the formation of oxidized species of LDL. However, it remains unclear what the ultimate impact of increased micronutrient intake will be on the overall health and longevity of the U.S. population.



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