It used to be that food was our sole source of vitamins and minerals. Today, nutrients can be obtained by consuming all kinds of supplements and a wide range of fortified foods, from cereals and juices to breads and energy bars. With all these choices at hand, it can get tricky figuring out how much of any one nutrient is enough. Many consumers feel that if a little is good, more must be better. But the truth is that consuming high levels of some nutrients can be dangerous and lead to irreversible health problems. Now, for the first time, guidelines have been issued to advise us on the safe upper limits for vitamins and minerals.
These guidelines are called Tolerable Upper Intake Levels, or ULs. The ULs are part of a bigger project, the Dietary Reference Intakes (DRIs), a new, comprehensive tiered system that determines nutrient intake levels for healthy individuals and groups (Trumbo et al. 2001). The DRI system will ultimately replace the Recommended Dietary Allowance (RDA) system in the United States and the Recommended Nutrient Intake system in Canada (Trumbo et al. 2001). The DRI project is a collaborative effort between the National Academy of Sciences (NAS) of the United States and its Canadian equivalent, Health Canada.
First published in 1941 by the NAS Food and Nutrition Board (FNB), the RDAs have served as the guidelines for adequate nutrient intake levels for decades. Based on scientific knowledge, these levels were considered adequate to meet the known nutrient needs for most healthy people. Since the RDAs were last updated in 1989, there has been a tremendous increase in research on the roles various nutrients play in promoting good health and the relationship between nutrient intakes and chronic disease. The FNB, in collaboration with Health Canada, performed a comprehensive review of the new scientific research; this review resulted in the creation of the new DRIs, which update and expand on the RDAs (NAS 1996). Like the RDAs, the DRIs are designed to meet the nutrient needs of healthy people who are free from diseases or conditions that may alter their daily nutrient needs (IOM 2000a). (Additional research still needs to be done to address the special nutrient needs of individuals with specific health issues and concerns.) Unlike the RDAs, which provided only a single reference value for a given nutrient, the DRI system now provides several values for each nutrient.
The new system represents a departure from the past in yet another way. The old RDAs focused on preventing nutrient deficiencies, whereas the DRI system instead emphasizes the benefits of eating well to optimize health and physical function (IOM 1999). Osteoporosis, cancer and cardiovascular disease are just some of the chronic conditions that may be prevented when the DRI levels are consistently met (NAS 1996). However, health problems can develop if nutrient intake is excessive, which is why ULs have been established.
The DRIs represent a new approach to nutrient intake levels in that the system is multileveled, offering guidelines for both optimum and maximum amounts. Following an exhaustive scientific review process by various FNB panels, committees and public hearings, the DRIs are being published as a series of seven reports. Each report addresses a different nutrient group. The four reports published to date focus on the nutrients related to bone health; folate and other B vitamins; antioxidants; and trace elements. Three other reports not yet published will look at macronutrients (protein, fat and carbohydrates); electrolytes and water; and other food components (e.g., fiber, phytoestrogens) (NAS 1996).
The DRIs include the following three types of reference values that apply to consumers (a 4th value applies to nutrition policy makers):
RDA. The RDA is the optimum daily intake level recommended for a particular nutrient. In the DRI system, the RDA values for some nutrients have changed only minimally since they were last updated in 1989. However, the current values are considered the “new” RDAs, because they are based on a comprehensive review of the latest scientific data.
Adequate Intake (AI). The AI is the optimum daily intake level recommended when an RDA could not be determined, due to lack of scientific data.
UL. The UL is the maximum daily intake level that should not be exceeded. Unless otherwise noted in this article, the UL refers to the total intake of a nutrient from all sources, including foods, water, fortified foods and supplements.
For more detailed descriptions of these tiered intake levels, see “The New DRI Values” on page 29.
The inclusion of ULs is the unique part of the DRIs. Simply put, the UL for a specific vitamin or mineral is the highest daily intake level that is unlikely to cause any ill health effects in the general population. While a healthy body could tolerate the UL intakes, they have not been found to provide any additional health benefits over the RDAs or AIs. It is important that consumers understand that ULs are not the recommended intake levels for nutrients. Instead, consumers should aim to consume the new RDA and AI levels set for different vitamins and minerals. (See “Daily Vitamin & Mineral Intake Levels for Adults” on pages 30 and 31.)
The UL for each nutrient was determined after a comprehensive study of toxicity data that analyzed any adverse health effects reported (IOM 2000a). Levels were then set for various amounts of the nutrient consumed. For example, if 100 milligrams (mg) was the highest level at which no adverse effects had occurred in any individuals, 100 mg would become the No Observed Adverse Effect Level (NOAEL) for that particular nutrient. If several people had begun to show some sign of toxicity at the 100 mg intake level, it would become the Lowest Observed Adverse Effect Level (LOAEL) for the nutrient. To account for variables in the data, an “uncertainty factor” was determined by a risk assessment, for safety reasons (the smaller the ascertained risk, the smaller the uncertainty factor). The NOAEL (or LOAEL if no NOAEL was available) was then divided by the uncertainty factor (IOM 2000a). So if the NOAEL had been set at 100 mg and an uncertainty factor of 2 was used, the UL for that nutrient became 50 mg (Liebman 2001).
According to Robert Russell, one of the physicians who served on the DRI panels, the ULs were based on the first side effects exhibited, not necessarily on those that were most serious (Liebman 2001). For example, when individuals consume too much niacin, the first side effect noted may be flushing, or a redness of the skin caused by blood vessels dilating. The UL for niacin was set at 35 mg per day based on the intake level at which this side effect first appeared (IOM 2000a). Yet physicians regularly prescribe niacin at doses as high as 5,000 mg daily in an effort to reduce high cholesterol levels.
Therefore, on some occasions—under a doctor’s supervision—it can be safe to take a nutrient at pharmacologic levels above the UL (Liebman 2001). The reason for this discrepancy is that the DRI panels used the most conservative values when setting the ULs, in order to protect the general population. So, even if a nutrient is consumed at the UL on a daily basis, that level should be safe for most healthy individuals. However, the higher the intake is over the UL, the greater the risk is for negative health effects—especially if the nutrient is consumed at that level on a long-term basis (Liebman 2001).
In general, it is unlikely that an individual could exceed a UL from food alone, even if the food had been fortified with a nutrient. According to Paula Trumbo, PhD, senior program officer at the FNB and director of the panel that determined the DRIs for micronutrients, “Exceeding the UL is more likely to happen when taking dietary supplements.”
Regularly consuming fortified foods while taking a daily supplement can lead to toxic levels of a given nutrient. For example, if a client takes an over-the-counter multivitamin supplement that contains 400 micrograms (mcg) of folic acid, while also eating fortified foods like cereals (400 mcg/1-ounce serving), pasta or rice (60 mcg/1 cup) and bread (20 mcg/slice), he or she could exceed the daily UL of 1,000 mcg for folic acid (IOM 2000a).
Nutrients commonly found in supplements and fortified foods include vitamins A and D, calcium, folic acid, iron and zinc.
Because nutrition is a relatively young science, not enough definitive data are currently available to set ULs for all nutrients. The sections below describe only those nutrients for which ULs have been established; unless otherwise noted, the ULs refer to the total intake from food, water, fortified foods and supplements. For the respective RDAs or AIs, good food sources and other information regarding these nutrients, see “Daily Vitamin & Mineral Intake Levels for Adults” on pages 30 and 31. The following sections describe the nutrients in the order in which the new DRI reports were released.
Calcium is best known for its role in building strong teeth and bones. It is also essential for nerve transmission, muscle contraction and blood clotting. Recommendations for this nutrient were set at levels related to maximum retention of body calcium, since calcium-rich bones are stronger and less susceptible to breaking. The new RDA for calcium for adults is 1,000 to 1,200 mg, depending on age. The UL has been set at 2,500 mg. Consuming chronically high doses of calcium above the UL can lead to renal problems, such as kidney stones, or block the absorption of other nutrients, such as iron and zinc (IOM 1999).
Unfortunately, most Americans and Canadians do not consume enough calcium-rich foods to meet the RDA. According to Edee Hogan, RD, LD, spokesperson for the American Dietetic Association in Washington, DC, “Food intake surveys indicate that women, especially postmenopausal women, don’t get enough calcium in their diet. If the RDA can’t be achieved through food, take a calcium citrate supplement. To boost absorption, look for a supplement with added vitamin D and take it with meals so the gastric juices are hard at work.”
Excellent food sources of calcium that provide approximately 300 mg per serving include low-fat milk and yogurt (1 cup); hard cheese (11/2 ounces); low-fat cottage cheese (11/4 cup); dark green leafy vegetables (1-2 cups cooked); and broccoli (2 cups cooked). Other good sources are tofu processed with calcium, canned fish with edible bones, legumes (Garrison & Somer 1995) and calcium-fortified foods, such as orange juice, sports bars, bread, crackers and cereals.
Magnesium is a major constituent of bone and is instrumental in regulating body temperature, nerve transmission and muscle contraction, while also helping to make proteins (IOM 1999). The new RDA for magnesium is 320 mg for women, 420 mg for men. The UL is 350 mg from supplements and fortified foods only; consuming more than the UL can cause diarrhea, nausea and abdominal cramping (IOM 1999). However, additional amounts can be consumed through naturally occurring foods without causing harm.
Food sources of magnesium include nuts, legumes, whole-grain cereals and breads, soybeans, seafoods and dark green vegetables. Lesser amounts are found in milk, meat, poultry and eggs (Garrison & Somer 1995).
Phosphorus is a structural component of all cells, important for the growth of bone and soft tissue (like muscle). A delicate balance exists between phosphorus intake and calcium stores in the body; excessive phosphorus levels can cause calcium to be depleted from the bones.
The new RDA is 700 mg for adults. The recommended daily intake levels are considered sufficient to support normal bone growth and metabolism at various life stages. The UL varies depending on age; for adults under age 70, the UL is 4,000 mg, whereas for those over age 70, it is 3,000 mg. Consuming more than the UL can weaken bones, increasing the risk of osteoporosis (IOM 1999).
Since phosphorus is a part of all cells, it is found abundantly in animal products, such as meats, fish, poultry, eggs and dairy products. Phosphoric acid is a preservative that is often added to processed foods (Garrison & Somer 1995). Processed and prepared foods and soft drinks can easily contribute to excessive phosphorus intake. A 12-ounce can of soda contains as much as 500 mg per serving!
Vitamin D plays a major role in bone health, regulating calcium and phosphorus absorption and deposits into bone. Vitamin D deficiency can accelerate osteoporosis and other bone problems (IOM 1999). Because vitamin D is naturally found in very few foods, the main source of this vitamin for most people is exposure to the sun. In general, individuals who spend about 15 minutes a day in sunlight (without sunscreen) do not need to consume food sources of vitamin D. For individuals who do not receive daily doses of sunshine, the new RDA varies depending on age: 200 international units (IU) for people aged 19 to 50; 400 IU for those aged 51 to 70; and 600 IU for those over age 70 (IOM 1999). The UL for vitamin D is 2,000 IU. Consuming more than this amount can elevate blood calcium levels, leading to potential kidney and heart damage (IOM 1999).
As we age, the body has a more difficult time converting vitamin D to its active form. To further compound this, the gut has fewer receptors to absorb vitamin D, leading to malabsorption. It can become difficult for older individuals to achieve the RDA for vitamin D through food sources; in consult with a nutrition expert, they may consider dietary supplements to reach the recommended intake (IOM 1999).
Food sources of vitamin D include fatty fish and fish oils, with varying amounts found in egg yolk, butter and liver. The most practical source is milk fortified with vitamin D. Strict vegetarians should consider a supplement if daily sun exposure is not possible (Garrison & Somer 1995).
Fluoride can be found naturally in some community water systems and in other areas is added to the water systems to reduce dental decay. The new AI for fluoride is 3 mg for women, 4 mg for men. These levels have been shown to reduce tooth decay without causing teeth discoloration (IOM 1999). The UL for fluoride is 10 mg. Consuming this amount on a long-term basis can cause discoloration of the teeth and bone problems (IOM 1999).
Folate works in tandem with vitamin B12 to metabolize proteins. Folate is also involved in the production of neurotransmitters (chemicals that help send messages between nerves) that regulate sleep, pain and mood (Garrison & Somer 1995). Folate is the form naturally found in foods, whereas folic acid is the synthetic version (found in supplements and fortified foods), which seems to be absorbed more easily. Because this nutrient can help reduce the risk of neural tube defects in newborns, childbearing women should be sure to consume the new RDA of 400 mcg daily. This can be obtained from fortified foods, vitamin supplements or a combination of the two. Women in their childbearing years should be sure to vary their diet so it includes some naturally occurring folate. The UL for this nutrient is 1,000 mcg, exclusive of food folate. Too much can mask or lead to a B12 deficiency, potentially causing irreversible nerve damage. Individuals most at risk are those who do not eat animal foods (IOM 2000a).
Since the term folate is derived from the word foliage, it should come as no surprise that the best natural sources of this nutrient are dark green vegetables. At least one to two servings of these folate-rich vegetables should be consumed daily. Other good food sources of folate include organ meats, kidney beans, beets, cabbage, yeast, cauliflower, orange juice, cantaloupe, sweet potatoes, wheat germ, whole-grain cereals and breads, and lima beans (Garrison & Somer 1995). Since manufacturers began fortifying grain products with folic acid, it has become easier to achieve adequate folic acid levels through diet. According to Hogan, “Intake of folic acid has increased tremendously now that it has been incorporated into flour [products].” In fact, some experts have expressed a concern that some people may be consuming an excessive amount of folic acid through fortified foods and supplements (IOM 2000a). To guard against either too much or too little folic intake, consumers need to carefully read food labels. In the case of a folate deficit, a vitamin supplement may be necessary.
Niacin is involved in more than 50 metabolic reactions, many of which help release energy from carbohydrates. Also known as vitamin B3, this nutrient plays a role in the formation of red blood cells (Garrison & Somer 1995). The new RDA for niacin is 14 mg for women, 16 mg for men. The UL is 35 mg; consuming more than this through supplementation can cause flushing of the skin (burning, tingling, itching, redness), nausea, vomiting and possibly liver damage (IOM 2000a).
The best food sources of niacin are those that contain protein—for example, meats, peanuts, poultry, legumes, milk and eggs. Moderate sources include orange juice, as well as whole-grain and enriched flours, cereals and breads (Garrison & Somer 1995).
VITAMIN B 6
This water-soluble B vitamin is essential for numerous steps in protein metabolism. Additionally, it is involved in carbohydrate, fat and cholesterol metabolism; hemoglobin production; and the proper function and growth of red blood cells (Garrison & Somer 1995). Vitamin B6 also affects the metabolism of calcium and magnesium. A powerhouse of a vitamin, B6 is primarily stored in the muscle, where it converts glycogen to glucose for energy. The new RDA for adults varies, depending on age and gender. For adults aged 19 to 50, the RDA is 1.3 mg; for women over age 50, it is 1.5 mg; and for men over age 50, it is 1.7 mg. The UL for all adults is 100 mg. Taking supplements above this amount can adversely affect the nervous system, resulting in reversible nerve damage that manifests itself in burning, tingling or shooting pain and/or numbness (IOM 2000a).
The best food sources of vitamin B6 are those that are rich in protein, such as red and organ meats, poultry, fish, egg yolk, soybeans, dried beans, peanuts and walnuts. Good sources include bananas, avocados, cabbage, cauliflower, potatoes, prunes and whole-grain cereals and breads (Garrison & Somer 1995).
Choline is a member of the B-complex group, which recent research has indicated may play a role in reducing heart disease, cancer and various mental disorders. Choline itself is involved in fat and cholesterol metabolism and the production of neurotransmitters; it can also reduce or prevent the buildup of excessive fat in the liver (IOM 2000a; Lieberman & Bruning 1997). The new AI for choline is 425 mg for women, 550 mg for men. The UL for all adults is 3,500 mg. Intakes higher than this have been associated with a fishy body and breath odor, sweating, diarrhea, low blood pressure and liver problems (IOM 2000a).
Food sources of choline include legumes, red and organ meats, milk and whole-grain cereals. Egg yolk is a particularly good source of this nutrient.
Vitamin C is one of several antioxidants that recent studies indicate may optimize health and reduce chronic diseases, such as heart disease, some forms of cancer and neurodegenerative conditions (NAS 2000b). Essentially, antioxidants help protect cells from damage caused by free radicals, which are highly reactive forms of oxygen and nitrogen that result from metabolic processes in the body and also from exposure to pollution, smoke and sunlight. In addition to its role as an antioxidant, vitamin C plays a major role in the formation of collagen (intracellular cement), which forms the basis for connective tissue (Garrison & Somer 1995). The RDA for vitamin C depends on gender and whether or not the individual is a cigarette smoker. For women, the RDA is 75 mg; for men, it is 90 mg. Smokers need to consume an additional 35 mg per day due to an increased need for antioxidant protection. The UL for vitamin C is 2,000 mg. Amounts higher than this can cause diarrhea or kidney stones, especially in persons with renal disease (IOM 2000b). Many people take vitamin C supplements when ill; research has shown that doses ranging from 500 to 1,000 mg can decrease the duration and severity of the common cold in some people (NAS 2000a).
Food sources of vitamin C are primarily fruits and vegetables, including citrus fruits, tomatoes, dark green and leafy vegetables, broccoli, cantaloupe, strawberries and potatoes (Garrison & Somer 1995).
Vitamin E acts as both a fat-soluble antioxidant and an anticoagulant (blood thinner) (NAS 2000a). While eight naturally occurring forms of vitamin E are found in food—they include four tocopherols and four tocotrienols (with alpha, beta, gamma and delta forms existing in both groups)—only the alpha-tocopherol form appears to be active in the body.
The RDA for daily vitamin E intake for adults is 15 mg, which is equivalent to 22 IU of “natural source” vitamin E or 33 IU of the synthetic form (NAS 2000b) (these numbers vary based on absorptive differences between the two forms). The UL is 1,000 mg for adults; this amount is equivalent to approximately 1,500 IU of natural source vitamin E or 1,100 IU of the synthetic form (NAS 2000b). Supplementing at an amount above this level may result in internal hemorrhaging.
The best food sources of vitamin E include nuts, seeds and their oils; vegetable oils; and leafy green vegetables. Hogan recommends regularly consuming a handful of nuts as part of a balanced diet to get the health benefits. “Tree nuts, especially almonds, are a good source of vitamin E,” he says. “Toasted almonds, paired with dried cranberries, make a nutritious and satisfying snack.”
Selenium’s role as an antioxidant begins in the body either alone or in the enzyme systems that defend against free radical damage. The RDA for adults is 55 mcg, to maximize enzyme activity. The UL is 400 mcg; at higher levels, individuals can develop a condition called selenosis (hair and nail loss) or experience gastrointestinal upset, skin rash, fatigue or garlic breath (IOM 2000b).
Food sources of selenium include seafood, liver, meat, milk and eggs. The selenium content of grains and vegetables will vary, depending on the soil conditions they were grown in (Garrison & Somer 1995).
Vitamin A is a fat-soluble vitamin that is stored in the liver and is essential for eyesight, immune function, reproduction, growth, gene expression and healthy skin (IOM 2001; Garrison & Somer 1995). The substances that form vitamin A fall into two groups: the retinoids, which are the active form used by the body and are found in animal foods; and carotenoids, which the body converts into the active form and are found in fruits and vegetables. Beta-carotene is commonly found in supplement form and is the type usually recommended as a vitamin A supplement (IOM 2001).
The new RDA for vitamin A is 700 mcg for women; for men it is 900 mcg. These levels should provide adequate stores in the body (IOM 2001). According to Trumbo, one of the main findings in the recently released DRI reports was the recognition that twice as much of the carotenoid form needs to be eaten daily as was previously thought. The UL for the retinoid form of vitamin A is 3,000 mcg (or 10,000 IU), as higher amounts can result in toxicity; no UL has been set for the carotenoid form of vitamin A or beta-carotene (IOM 2001). Many multivitamins and supplements contain more than the RDA, so reading labels is essential.
According to Trumbo, excessive vitamin A intake can cause birth defects and irreversible liver damage in adults.
The retinoid form of vitamin A is found only in animal sources, such as fish oils, liver, whole milk and milk fortified with vitamin A. The carotenoid form is found in dark green, yellow and orange fruits and vegetables like kale, spinach, apricots, carrots and cantaloupe (Lieberman & Bruning 1997). Trumbo recommends that strict vegetarians eat more dark-colored fruits and vegetables to meet their vitamin A requirements.
This trace element is involved in the development of nerve, bone, blood and connective tissue. For adults, the new RDA for copper is 900 mcg. The UL was set at 10 mg (10,000 mcg), to protect against liver damage (IOM 2001).
Food sources include whole-grain breads and cereals, seafood, nuts, organ meats, eggs, poultry, legumes and dark green leafy vegetables. Foods that contain lesser amounts include fresh and dried fruits and vegetables, milk and milk products and tea (Garrison & Somer 1995).
Iodine’s primary role is in helping produce the thyroid hormones that regulate metabolism. An iodine deficiency over several months can cause hypothyroidism, goiter (enlarged thyroid gland) or mental retardation.
The new RDA for adults is 150 mcg, to ensure that the thyroid gets sufficient iodine to perform its metabolic functions. The UL was set at 1.1 mg (1,100 mcg), to prevent overabsorption and thyroid problems (IOM 2001).
The best food sources are iodized salt and water that contains iodine. Individuals who consume a low-sodium diet may need to consult a nutrition expert to see if they are getting sufficient amounts of iodine. Other food sources, like plants and seafood, have varying iodine concentrations due to different soil and sea levels of iodine.
Iron is essential for transporting oxygen in the bloodstream. It also plays an important role in collagen synthesis, immune function and the prevention of anemia. Iron needs are higher during pregnancy (for fetal growth) and also during the premenopausal years (when iron is lost through menstruation).
The new RDA is 8 mg for men and postmenopausal women; 18 mg for premenopausal women; and 27 mg for pregnant women. Because it can be difficult for pregnant women to eat that much iron, a supplement (usually in the form of a prenatal vitamin) is typically recommended (IOM 2001). The UL for iron is 45 mg for adults. Consuming more than this amount may cause gastrointestinal upset (constipation, nausea, diarrhea), especially when iron is taken on an empty stomach. While inconclusive, some studies have linked elevated iron stores to an increased risk of heart disease and cancer (IOM 2001). The UL does not protect people who have hemochromatosis, a condition in which dangerously high levels of iron are stored in the body.
Iron is found in red meat, dried fruits, legumes, dark green leafy vegetables, prune juice, tuna, chicken, nuts and whole-grain and enriched breads and cereals (Garrison & Somer 1995). Vegetarians may have to eat twice the RDA since iron absorption from plant sources is less efficient than it is from animal sources (IOM 2001).
Manganese plays a role in bone formation and in the metabolism of protein, carbohydrate and fat. The new AI was set at 1.8 mg for women, 2.3 mg for men. The UL was set at 11 mg, to prevent the types of neurological problems seen at higher levels (IOM 2001).
Excellent food sources of manganese include lettuce, spinach, liver, kidney, muscle meats, tea, legumes, nuts and whole-grain breads and cereals (Garrison & Somer 1995).
This trace mineral plays a role in two enzyme systems and iron metabolism. The new RDA for adults is 45 mcg. The UL was set at 2 mg (2,000 mcg), based on animal studies that showed reproduction and growth problems at chronically high levels of intake.
Food sources of molybdenum include whole grains, breads, cereals, legumes, leafy vegetables and nuts (IOM 2001; Garrison & Somer 1995).
Zinc is found in all body tissue and is involved in more than 100 enzyme systems! It is essential for insulin activity, protein synthesis, bone structure, gene expression, immune system function and wound healing (IOM 2001; Garrison & Somer 1995). The RDA is 8 mg for women, 11 mg for men. The UL was set at 40 mg because higher levels can block the absorption of copper (IOM 2001).
Food sources of zinc include red meats, some seafood (like oysters), milk, egg yolk and whole-grain breads and cereals (Garrison & Somer 1995). The zinc found in plant foods is not absorbed as well as that found in animal sources. As a result, vegetarians may need to consume up to 50 percent more zinc than nonvegetarians.
Nutrition is an evolving science. The current DRI reports offer the most comprehensive review of scientific literature based on what we know now. The benefit of the new DRI tiered approach is that, as scientific understanding continues to expand, the DRIs will be updated accordingly. For healthy consumers, the DRIs can serve as a guide for nutrient intake to optimize health and energy levels. You can help your clients understand the need to assess what they are currently consuming to determine if they are meeting or exceeding the recommended amounts of essential nutrients.
Research continues to underscore the health benefits of a plant-based diet rich in fruits, vegetables and whole grains, with ample protein and healthful fats. Hogan says you can help your clients achieve this kind of diet on a regular basis by using a few practical strategies. “Suggest they do a ‘plate checkup,’” she advises. “Check the plate for color, balance (too much of one thing, too little of another) and portion size. People need to put more planning into food purchasing and have lots of convenient and readily available foods around. When in doubt, a one-a-day multivitamin that doesn’t exceed 100 percent of daily requirements is a good way to hedge your bets.”
Garrison, R., & Somer, E. 1995. The Nutrition Desk Reference. New Canaan, CT: Keats Publishing.
Institute of Medicine (IOM). 1999. Food and Nutrition Board (FNB). Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. Washington, DC: National Academy Press.
IOM. 2000a. FNB. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin and Choline. Washington, DC: National Academy Press.
IOM. 2000b. FNB. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium and Carotenoids. Washington, DC: National Academy Press.
IOM. 2001. FNB. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium and Zinc. Washington, DC: National Academy Press.
Liebman, B. 2001. Vitamins & minerals: How much is too much? Nutrition Action Healthletter (June).
Lieberman, S., & Bruning, N. 1997. The Real Vitamin & Mineral Book (2nd ed.). New York: Avery Publishing Group.
National Academy of Sciences (NAS). 1996. Frequently asked questions about the DRIs. Washington, DC: National Academies.
NAS. 2000a. Dietary Reference Intakes for vitamins C and E, selenium and carotenoids: Frequently asked questions and answers. Washington, DC: National Academies Office of News and Public Information.
NAS. 2000b. Antioxidants’ role in chronic disease prevention still uncertain; huge doses considered risky. Washington, DC: National Academies Office of News and Public Information.
Trumbo, P., et al. 2001. Dietary Reference Intakes: Vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, vanadium and zinc. Journal of the American Dietetic Association, 101 (3), 294-300.
The new DRI system employs a tiered approach, setting optimum and maximum levels for different nutrients. Here is a breakdown of the new system:
The RDA is the intake that meets the nutrient needs of almost all the healthy individuals in a life-stage (specific-age) and gender group. Consumers should use the RDA as a guide to achieve adequate nutrient intake to help reduce the risk of chronic disease.
When an RDA cannot be established due to lack of scientific evidence, an AI is set. The AI should be used as an intake goal when no RDA exists. AIs are based on fewer data and more judgment than RDAs. Each AI level set has been shown to support a desired indicator of health, such as calcium retention in bone.
The UL is
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