Establishing A Suggested Optimal Nutrient Allowance (SONA)
The Weakness of the RDAs
In May of 1941, a committee of the National Academy of Sciences suggested for the first time a "Recommended Daily Dietary Allowance" of nutrients. These guidelines were developed in the hope of reducing the incidence of nutritional deficiency diseases such as scurvy (deficiency of vitamin C), pellagra (deficiency of niacin) and beri-beri (deficiency of B-1) in the general population. Since then, nutritionists, dieticians and physicians have relied on this reference standard and its many revisions commonly referred to by its abbreviation, the RDA.
The RDAs (Council, 1980 544) (Council 1989 1201) were intended:
Point two is important since it is a common fallacy to use the RDAs to evaluate the adequacy of an individuals diet by comparison to these population guidelines.
It is and even graver error to associate the RDAs with levels of nutrient intake able to insure the maintenance of health over a life-time. Only recently has it become apparent that "healthy normal people" are an ideal rather than a practical concept. Among Americans aged 60 and over, more than 80 percent suffer from at least one chronic disease, such as cancer, atherosclerosis, osteoporosis, macular degeneration of the eye, or diabetes.
Since at least 1951, critics of the RDAs (Proudit, 1951 1203, p.176) have pointed out that the RDAs lack the ability to recommend levels of nutrients sufficient to maintain health for one's whole life span. Studies to determine the level of any nutrient sufficient to prevent a nutritional deficiency were conducted for periods of up to 6 to 9 months, or about 1 percent of the average human life span. Nutritional studies with animals have shown again and again that the amounts of some nutrients sufficient to provide health and the prevention of a deficiency disease for short periods of time may be totally inadequate in maintaining the health of the animal over its entire life span. This may be one reason that these minimal dietary standards are incapable of providing the levels of nutrients essential to prevent many chronic diseases.
Even earlier editions of the RDAs published in the 1940's clearly stated that the RDAs "vary greatly in disease." (Council, 1948 1202) In spite of this realization the RDAs continued to focus only on the prevention of nutritional deficiencies in population groups. That was until 1989, when the 10th edition of the RDAs was released by the National Academy of Sciences (Council, 1989 1201). This newest edition acknowledged for the first time that levels of a nutrient, specifically vitamin C, may need to be higher than the RDA for groups at risk of developing chronic diseases, particularly smokers. This welcome recommendation by the National Academy of Sciences has opened the door for the use of an entirely different approach in determining the optimal levels of nutrients needed to minimize the risk of developing chronic diseases in various population groups. Even the RDA’s noble attempt to suggest higher levels of vitamin C intake for smokers is inadequate. Studies of smokers have found that their blood levels of vitamins and minerals are also low in beta-carotene, zinc, vitamin B-6 and vitamin E. Increasing evidence suggests that the reduced levels of these nutrients along with vitamin C may contribute to common health risks associated with smoking.
Yet the RDA fails to address the regular use of alcohol which is another example of an addiction that increases nutrient requirements. Individuals who chronically consume alcohol have been found to have lower levels of folate, vitamin B-1, vitamin B-6, vitamin A, beta-carotene, zinc and vitamin C.
Life styles of individuals are also neglected in the RDAs. Dieters, for example, are a population who have frequently been found to have low nutrient status. Studies have shown that is extremely difficult if not impossible to meet all the RDAs for nutrients, let alone maintain health, when consuming less than 1200 calories per day. Analysis of 11 major reducing diets showed that none could provide 100 percent of the RDAs for vitamins.
In summary, individuals may have habits or life styles that require nutrient levels far in excess of that recommended by the RDAs. Chronic consumption of alcohol and a host of other habits, life style and environmental risks (e.g. carbon monoxide, lead, mercury) associated with our complex society, may at some point have to be addressed in future revisions of the RDAs.
The Need for a Guideline to Optimal Levels of Nutrients
Of even greater significance is a growing body of evidence that indicates that intakes of certain vitamins and minerals above the RDAs may be necessary to protect against the development of certain chronic diseases. For example, antioxidants, such as vitamin C, beta-carotene, and vitamin E, may prevent the damage to vascular endothelial cells by free radicals associated with a common form of cardiovascular disease, atherosclerosis. These vitamins may be required in much higher amounts than the RDA to prevent atherosclerosis than needed to prevent deficiency symptoms. Unless, of course, the development of atherosclerosis is a deficiency symptom of these vitamins. The same might be true of many cancers, heart disease, or eye diseases (e.g. macular degeneration or cataracts).
There is also no claim by the National Academy of Sciences that the RDAs are intended as "ideal" daily intakes for the maintenance of optimal health. Many people would like to know what the "optimum" intake of various nutrients should be to maintain long term good health, or prevent the progression of a chronic disease.
Through the effort of a 15-year study it is now possible to extrapolate suggested optimum daily nutrients allowances, or SONA’s. These SONA’s are levels of nutrients found in a study of 13,500 male and female subjects living in six regions of the United States conducted by senior investigators, Drs. Emanuel Cheraskin and W. M. Ringsdorf Jr. of the University of Alabama School of Medicine. The results of their two million dollar study are contained in 49,000 bound pages found in 153 volumes, whose results have been published in over 100 papers during the 1970's and 1980's.
In this university study, each subject had completed:
This study attempted to find a truly "ideal" daily consumption of nutrients, carbohydrates, protein, and fat, on the logical hypothesis that relatively symptomless and sign-free persons are healthier than those with clinical symptoms and signs of disease. Simply, the study of dietary and supplemental intakes of symptomless and sign-less groups provides the basis for determining what should be the "ideal" daily nutrient level.
This approach consistently revealed that the healthiest individuals, meaning those with the least clinical symptoms and signs of disease had consumed supplements and eaten a diet rich in nutrients relative to calories.
Using this method, for example, it was discovered that the "healthiest" subjects had a mean vitamin C intake of 410 milligrams (mg) a day. What is particularly noteworthy about this level of vitamin C is that in a study of the diet of primitive man, published in the New England Journal of Medicine, it was found that our remote ancestors consumed 392 mg of vitamin C a day. The finding of 410 mg of vitamin C in "healthy" modern man, and 392 mg in primitive man, is only a difference of 4 percent! Further evidence to date suggests that the incidence of cancer and other chronic diseases of modern civilization was rare in primitive man. Could the higher intake of vitamin C and other nutrients in primitive diets and their lower incidence of chronic degenerative diseases be related?
Epidemiologic evidence of a protective effect of vitamin C for non-hormone-dependant cancers is strong, according to a 1991 National Cancer Institute report published in the American Journal of Clinical Nutrition. (Block, 1991 1208) Of the 46 studies in which dietary vitamin C was calculated, 33 found statistically significant protection against cancer, with the highest intakes above the RDA conferring the highest protection. Of 29 additional studies that assessed fruit intake, 21 found significant protection. For cancers of the esophagus, larynx, oral cavity, and pancreas, evidence for a protective effect of vitamin C or some component in fruit (i.e. bioflavonoids, carotenoids) is strong and consistent. For cancers of the stomach, rectum, breast and cervix there is also strong evidence of a protective effect against cancer. Several recent lung cancer studies also found significant protective effects of vitamin C, therefore, the concept of an "ideal" or suggested optimum daily nutrient allowance (SONA) of 410 milligrams of vitamin C seems reasonable, even though it is several fold above the RDA level for vitamin C suggested to prevent scurvy.
At present, the RDAs represent the nutritional equivalent of the minimum wage. Just like the minimum wage, they offer little hope of significantly improving the quality of your life. Clearly, there is a profound need for SONA’s to supplement the outmoded RDAs. SONA’s represent the first nutritional guidelines designed to maintain health over a lifetime.
Survey questions for SONA’s:
Long Term Benefits of Regular SONA Consumption
The researchers summarized the long term benefits that the average person could expect if they were to consistently ingest vitamins and minerals at levels as established in the SONA study, along with practising healthy living habits.
Vitamin A is required for reproduction, the maintenance of epithelial tissue (i.e. skin, lung, vagina, uterus, gastrointestinal tract), and for vision. It may be important in cancer prevention and treatment of precancerous conditions. Beta-carotene is an ideal source for vitamin A, since it is the most nutritionally active vitamin A precursor among carotenoids and very safe. Beta-carotene is also referred to as a "provitamin" since it converts to vitamin A in the body. Of nearly 600 carotenoids from natural sources, less than 50 are vitamin A precursors such as beta-carotene. Beta-carotene and its related carotenoids can enhance immunity directly as an antimutagen and anticarcinogen, reducing cell damage, and protecting against various cancers developing in tissues. In particular, increased beta-carotene levels seem to decrease the chance of developing lung cancer, important information to cigarette smokers or those regularly exposed to side-steam smoke. Individuals with low intakes of beta-carotene have a 30 to 220 per cent higher risk of developing lung cancer than people with high intake of this nutrient. Beta-carotene also has non-vitamin A functions based on its ability to act as an antioxidant by scavenging free radicals. For example, carotenoids protect against excessive ultraviolet exposure that can lead to UV-related tissue damage and skin cancer. Vitamin A toxicity in adults is uncommon at doses below 100,000 IU per day, and when they develop, disappear within a short period of time. Since several cases of birth defects have been attributed to high doses of vitamin A, suggesting it may be teratogenic or embryotoxic at high doses, caution should be shown by pregnant women or women expecting to bear a child who are considering supplementation. Animal studies, however, have shown that beta-carotene is not mutagenic, teratogenic, embryotoxic, or carcinogenic, nor causes hypervitaminosis A (Vitamin A toxicity).
Vitamin A/Beta Carotene References:
Vitamin D is a prohormone classified as a vitamin. It is important for bone maintenance, metabolism and absorption of phosphorous and calcium, while also contributing to the functioning of the reproductive system, the digestive system and the immune system. Vegetarians, the elderly, and individuals receiving limited exposure to sunlight ultraviolet, may be at risk of inadequate vitamin D levels. There is epidemiological evidence, including one very large study of U.S. Navy personnel, that adequate vitamin D levels may decrease the chance of developing certain skin melanomas (skin cancers) in adults with occupations and life styles that prevent regular exposure to sunlight for up to 15 minutes a day. Good vitamin D status may be associated with reduced risk of hypertension while also playing a role in regulating blood pressure. The elderly may be at particular risk of poor vitamin D status due to decreased exposure to sunlight, decreased absorption of the nutrient in the gastrointestinal tract, and decreased caloric intake. The skin of elderly individuals also produce approximately half the vitamin D after exposure to the sun as produced by a much younger person. There is some evidence that vitamin D may play a role in reducing some types of cancer, such as colorectal cancer. Vitamin D can be toxic at prolonged (several months) high intakes. No adverse effects, however, have been found in healthy adults who have consumed up to 62 times the RDA of this nutrient. Since vitamin D has been shown to be teratogenic in animals, pregnant women, or a woman potentially bearing a child, should approach vitamin D supplementation with caution. Since sunlight ultraviolet exposure on the skin promotes vitamin D production, it is important to note that this process is self limiting and will not cause vitamin D toxicity (hypervitaminosis D) in healthy people.
Vitamin D References:
Vitamin E (Tocopherols and tocotrienols)
Vitamin E is essential to all mammals. Any deficiency of this vitamin may effect the lifespan of red blood cells, platelet activity, and can lead to neuromuscular problems. One of the most important functions of vitamin E is to protect cell membranes from damage by oxygen, known as "oxidative damage". Vitamin E plays a role in preventing mutagenesis, in the repair of membranes and DNA, and in maintenance of immunocompetence. A repeated number of studies have found that the incidence of various cancers are higher in individuals with low levels of vitamin E. This suggests that there may be an association between low vitamin E status and subsequent risk of developing some cancers. This is particularly important for smokers or those exposed to cigarette smoke, since vitamin E is a respiratory tract antioxidant. There is evidence that vitamin E inhibits platelet aggregation, a condition associated with blood clots that can potentially lead to myocardial infarcts or stroke. Vitamin E levels decline with age, suggesting increased intake of this nutrient with age. Both immunity and infection are enhanced by vitamin E supplementation in elderly people. Adequate vitamin E levels may also protect against cataract development. In one study, vitamin E supplementation reduced the risk of cataracts by more than half compared to those unsupplemented. The benefit of vitamin E supplementation is unclear for both recreational exercisers and high exercise-induced muscle injury. In general, high intake of vitamin E seems very safe. Very few side effects have been reported in any scientifically controlled studies, with intakes as high as 3,200 milligrams (3,200 I.U.) of vitamin E supplementation, is not, however, recommended for individuals receiving anticoagulant therapy who may also be vitamin K deficient. The suggested optimal levels are for natural Vitamin E (d-alpha tocopherol or d-alpha tocopheryl acetate or d-alpha tocopheryl succinate). All forms of natural vitamin E become active antioxidants (free radical scavengers) inside the body. The synthetic forms of vitamin E have the dl-designations in front of the form provided. If natural vitamin E is desired, be sure the label states that the source is 100% natural and that the potency has been independently assayed.
Vitamin E References:
Vitamin C (Ascorbic Acid)
Adequate vitamin C (Ascorbic Acid) intake is necessary for immunity, maintenance of bones, formation of collagen, and a broad range of other biologic functions. In a study of 1,038 doctors and their wives, studied for their vitamin C intake, the subjects with the least signs and symptoms of illness or degerative diseases consumed an average of 410 milligrams of vitamin C a day, about nine times that of the RDA for this essential nutrient. To achieve even this level of vitamin C intake requires supplementation. Individuals need to also consider the following information. Scientific evidence suggests that vitamin C may decrease the risk of developing cataracts, cancers of the gastrointestinal tract, while also reducing the risk of developing cardiovascular disease. Cigarette smoking is associated with a significant decrease in vitamin C levels. For a typical smoker to attain the same vitamin C level as a non-smoker requires twice the same vitamin C intake. Alcoholics also have low vitamin C status, and may require considerably more vitamin C owing to their physical condition. The elderly may especially benefit from vitamin C supplementation. Increased lipid (fat) peroxidation has been associated with accelerated ageing and degeneration. One study has demonstrated that much higher than RDA levels of vitamin C by supplementation over a one year period significantly decreased lipid peroxide levels in elderly subjects. The interest in vitamin C in the treatment of cancer is partially based on studies significantly reduced levels of the vitamin in patients with malignancies. Most evidence suggests that larger than RDA doses of vitamin C may be beneficial in reducing the risk of developing various cancers, rather than treating them. This may be due to the higher levels of vitamin C improving certain indices of immune competence and response that boost disease resistance. Studies have also shown reductions in healing time of wounds with high dose of vitamin C supplementation. Vitamin C may reduce the risk of cardiovascular mortality at levels well above the RDA, possibly by influencing cholesterol levels, platelets, and even blood pressure. Since the levels of vitamin C decline with age after mid-life, there is evidence that sub-optimal levels of vitamin C may increase the risk of cataracts. Those individuals who consume the lowest levels of vitamin C seem to have the highest incidence of cataractous lenses. One study has even shown that those subjects who supplemented with vitamin C significantly lowered their risk of developing cataracts. Vitamin C markedly increases nonheme iron absorption. In some diets, only 3% of nonheme iron is absorbed compared to as much as 23% of the heme in iron form. The addition of 50 to 100 milligrams of vitamin C with meals can double or triple nonheme iron absorption. Two grams (2,000 mg) of vitamin C taken throughout the day with meals increases the absorption of nonheme iron fivefold. Bone density and vitamin C status declines after age 35 and thereafter. One of the important nutrients involved in bone metabolism is vitamin C, especially in the synthesis of collagen which forms the structural framework of bones. A number of studies show that vitamin C supplementation results in improved maintenance of bone mineral density in postmenopausal women.
Vitamin C References:
Vitamin K is fat-soluble. The vitamin is found in food and also created by bacteria in our intestines. Its primary function is in the production of blood clotters or coagulators. There is also growing evidence that it plays a role in bone development. A normal mixed diet contains between 300 to 500 micrograms of vitamin K per day, well in excess of the RDA. There is insufficient evidence to suggest supplementation intake of vitamin K beyond that found in most diets.
Vitamin K References:
Thiamin (Vitamin B-1)
There is insufficient evidence to suggest intakes of thiamin above 8 times the RDA in healthy persons. However, individuals regularly consuming high intakes of refined carbohydrates (i.e. refined sugar-sucrose, wheat flour products made with unfortified 70% extraction flour) may require supplemental intake of thiamin in the range of 5 to 15 milligrams a day until such time as the diet improves. In a study of 1,009 dentists and their wives evaluated for daily thiamin intake, those subjects having the very least number of signs or symptoms associated with illness of degenerative diseases had been consuming an average of 9 milligrams of thiamin a day, approximately eightfold the RDA for this nutrient. To date, thiamin, when taken orally, has been reported harmless in humans.
Thiamin (Vitamin B-1) References:
Riboflavin (Vitamin B-2)
The need for riboflavin varies with energy requirements, explaining why riboflavin deficient people tire and have a poor appetite. Riboflavin is especially important for tissue repair, vision, and blood. There is growing evidence that riboflavin may be important in preventing the development of cataracts, commonly associated with aging. There is equivocal evidence that riboflavin supplementation may be required in those exercising regularly. This may be more of a consideration if the exerciser is on a calorie-restrictive diet. Riboflavin has no known toxicity. There is insufficient evidence to support riboflavin supplementation in healthy adults above twice the RDA.
Riboflavin (Vitamin B-2) References:
Niacin - nicotinic acid, nicotinamide (niacinamide)
Niacin is critical in many biochemical processes, particularly those involving energy metabolism and lipid metabolism. Much interest is due to its use as a drug-like agent that lowers LDL-VLDL-cholesterol and triglycerides, while increasing HDL cholesterol. There is also interest in its notorious, but not harmful, vasodilatory or "flushing" effect in increasing blood flow to the extremites in certain circulatory disorders. This effect comes only from the nicotinic acid form not the amide. There is no evidence that levels above twice the RDA for niacin in healthy persons prevents disorders associated with high cholesterol (hypercholesterolemia) or other hyperlipidemias. Because nicotinic acid can increase blood sugar levels, nicotinic acid supplementation is contraindicated in diabetics. Also large intakes of nicotinic acid (>1,000mg) has been associated with stomach pain, diarrhea, cardiac arrhythmias, itching, and nausea. The only evidence for a significantly higher intake of niacin above the RDA comes from a study of 1,053 dentists and wives. In this study it was found that in those individuals with the least number of signs and symptoms associated with physical illness or degeneration were consuming an average of 115 mg of niacin a day approximately six or seven times the RDA. Whether this single study should suggest this amount as optimal remains too speculative until additional studies are reported. Important note: Niacin is a vitamin whose requirements in humans is met in part by conversion of the essential amino acid tryptophan to niacin. Several studies have calculated that from 39 to 86 mg of tryptophan produce the same levels of niacin metabolites as 1 mg of niacin as equivalent to 60 mg of tryptophan.
Vitamin B-6 (pyridoxine, pyridoxal, pyridoxamine, and corresponding phosphorylated forms)
Vitamin B-6 is required for growth and maintenance of almost every bodily function, amino acid metabolism, and production of neurotransmitters derived from amino acids. It also plays a role in glycogen breakdown, fatty acid metabolism, hormone metabolism, heme biosynthesis and purine biosynthesis. Supplementation of vitamin B-6 has been used in treating carpal tunnel syndrome, premenstrual syndrome, cardiovascular disorders and diabetic neuropathy. Elderly people may have an increased requirement for vitamin B-6 to maintain health, particularly for their immune system. In one study, healthy elderly people were given either 50 mg/day of vitamin B-6 or placebo. Those supplemented had significant improvement in immunocompetence, especially lymphocytic activity. There is also preliminary evidence that inadequate vitamin B-6 status may contribute to the development of coronary heart disease by increasing plasma homocysteine. Homocysteine has been found to be highly atherogenic in animals and may contribute to atherosclerosis in humans. The added evidence that vitamin B-6 might be important in preventing cardiovascular diseases comes from experimental studies in animals. When these animals are given vitamin B-6 deficient diets they develop atherosclerotic lesions similar to those found in human atherosclerosis. Very high doses of vitamin B-6 have been associated with sensory and motor impairment. Daily intakes up to 500 mg ad day, which is 250 times the RDA, for up to six months appear to be safe. While there is increasing evidence for a role of vitamin B-6 supplementation it is in preventing some kinds of cardiovascular diseases and for enhancing immunity; optimal levels in healthy individuals need not exceed twelve to fifteen times the RDA, even in the elderly.
Vitamin B-6 (Pyridoxine) References:
Folic Acid (Pteroylglutamic acid)
Folic acid is required in the metabolism of some amino acids, for the synthesis of nucleic acids, and in a number of enzyme cofactors. Certain population groups are at particular risk in developing folate deficiency, especially pregnant women and adolescent females. Like newborn infants, which are also at risk, these groups experience considerable growth, confirming the importance of folic acid in protein synthesis and the DNA and RNA replication required in cell growth. Inadequate folic acid is also seen in the elderly, where it is less well absorbed. Since folic acid deficiency has been well documentation as a cause of birth defects in animals, numerous studies have looked at its role in such human congential malformations as neural tube defects, cleft palate, and cleft lip. Folic acid and multivitamin supplementation have been demonstrated in numerous studies to decrease or eliminate the recurrence of neural tube defects or cleft palate and cleft lip in human offspring. Folic acid may also reduce a risk factor associated with atherosclerosis. Folic acid is required for the conversion of homocysteine (homocystinemia), which is a risk factor for atherosclerosis. Normal subjects given 5 mg/day of folic acid for two weeks had significant decreases in homocysteine levels, especially in those whose initial homocysteine levels were high. Folic acid supplementation can mask clinical sign of pernicious anemia, which, if left untreated can lead to permanent nerve damage. There is also some continuing controversy about whether folic acid supplementation of 400 mcg or more reduces zinc absorption. To be on the safe side, until additional studies are completed, and optimal level of zinc intake is suggested.
Folic Acid References:
Vitamin B-12 is essential for the functioning of a number of enzymes involved in amino acid, nucleic acid, and fatty acid metabolism. It is also necessary in the metabolism of folic acid (folate). At least one study has found that some individuals with gastric disease have poor absorption of vitamin B-12 if it is in food, but not if in a crystalline supplemental form. Vitamin B-12 deficiency is rather common among the elderly, due to lack of gastric intrinsic factor, which causes vitamin B-12 malabsorption from food. When this condition occurs it is often seen as neurological, cerebral, or psychiatric abnormalities. In such cases an injectable form of vitamin B-12 has proven repeatedly to be a superior to any oral vitamin B-12 supplement. There is increasing evidence that vitamin B-12 may play a role in the prevention of some types of cancers. Smokers, for example, have been found to have significantly decreased levels of precancerous bronchial squamous metaplasia when given vitamin B-12 (500 mcg/day) and folic acid supplements than those receiving placebo. Although there is increasing evidence that vitamin B-12 may reduce one risk factor for arteriosclerosis, namely, an accumulation of homocysteine (homocysteinemia), too few studies exist examining this role to confirm its benefit in reducing this risk. Vitamin B-12 has not been found to be carcinogenic, teratogenic, or mutagenic. It is considered safe even at levels of 1000 times the RDA. Vitamin B-12 deficiency is more likely in very strict vegetarians, since the best sources of vitamin B-12 are meat and meat products and, to a lesser extent, milk and milk products, some seafood's, and egg yolk. There is insufficient evidence to advocate an intake of vitamin B-12 above the RDA in any population group, except in the elderly.
Vitamin B-12 References:
An adequate supply of zinc is essential for growth and physical development, especially as it relates to proteins, fats and carbohydrates. Most aspects of reproduction in both males and females requires zinc. This mineral is also vitally important to the immune system. Zinc is antagonistic to such toxic elements as cadmium, mercury and lead. Virtually every enzyme reaction in the brain involves zinc, and its essentiality in the development and continuous function of the central nervous system and brain is uncontested. Impairments of taste, vision, smell, and appetite are often early signs of inadequate zinc status. The typical intake of zinc in Western diets is around 10 milligrams, two-thirds the RDA. Some individuals seem to be poor absorbers, so need more zinc in their diet than the average person. There is a simple test for zinc status (zinc status, Ethical Nutrients, San Clemente, CA) that evaluates the ability to test a pre-mixed soulution of zinc. Individuals unable to taste this solution have been found to be zinc deficient, in some cases despite being asymptomatic. Insufficient zinc has multiple effects on the immune system, particularly T-lymphocytes, depression in number an activity of killer cells, and impaired antibody production. This association is particularly important in the elderly, who often consume less than half the RDA for zinc. As in the elderly, most cases of zinc deficiency whether chronic or marginal are self-inflicted. This may result from slimming diets, vegetarianism, or other lifestyle habits (i.e.- alcoholism, excessive exercise). However, in some cases, relative zinc deficiences are induced by inadvertent exposure to toxic metals, such as cadmium from cigarette smoke; or excess copper from copper water pipes. There is increasing evidence that zinc levels decline following physical stress or injury. Zinc is one of the few minerals lost more rapidly in the urine following acute or chronic psychological stress. In time this can lead to inadequate zinc status, despite RDA intake. The highest concentrations of zinc are in the ear and eye. Disorders associated with impairment of either organ may benefit from continuous optimal intakes of zinc over a lifetime. Zinc supplementation is generally safe if maintained at levels within two to eight times the RDA. Symptoms of zinc toxicity include gastrointestinal irritation, vomiting, adverse changes in HDL/LDL cholesterol ratios, and impaired immunity. The latter develops when levels above 180 mg/day are consumed for more than several weeks. Excessive intake of zinc may either lower copper levels or aggravate an existing marginal copper deficiency. There is insufficient evidence to suggest a zinc intake twice the RDA for zinc. However, since repeated studies of Westernized diets indicate the most populations consume less than the RDA if this essential mineral, it seems prudent that some supplementation of zinc or increase zinc-rich foods be considered a part of maintaining an optimal level of this nutrient over a lifetime.