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What is the Recommended Dietary Allowance for zinc for infants, children, and adults?
Table 1: Recommended Dietary Allowance for zinc for infants over 7 months, children and adults
When can zinc deficiency occur?
What are some current issues and controversies about zinc?
Zinc, infections, and wound healing
Zinc and the common cold
Zinc and iron absorption
What is the health risk of too much zinc?
Table 2: Upper Levels for Zinc for Infants, Children, and Adults
Zinc: What
is it?
Zinc is an essential mineral that is found
in almost every cell. It stimulates the activity of approximately 100 enzymes,
which are substances that promote biochemical reactions in your body (1,2).
Zinc supports a healthy immune system (3,4), is needed for wound healing (5),
helps maintain your sense of taste and smell (6), and is needed for DNA synthesis
(2). Zinc also supports normal growth and development during pregnancy, childhood,
and adolescence (7, 8).
What foods provide zinc?
Zinc is found in a wide variety of foods (2).
Oysters contain more zinc per serving than any other food, but red meat and
poultry provide the majority of zinc in the American diet. Other good food sources
include beans, nuts, certain seafood, whole grains, fortified breakfast cereals,
and dairy products (2,9). Zinc absorption is greater from a diet high in animal
protein than a diet rich in plant proteins (2). Phytates, which are found in
whole grain breads, cereals, legumes and other products, can decrease zinc absorption
(2, 10, 11).(Refer to Table 1: Selected Food Sources of Zinc lists a variety
of dietary sources of zinc.)
What is the Recommended Dietary Allowance
for zinc?
The latest recommendations for zinc intake are given in the new Dietary
Reference Intakes developed by the Institute of Medicine. Dietary Reference
Intakes (DRIs) is the umbrella term for a group of reference values used for
planning and assessing nutrient intake for healthy people. The Recommended Dietary
Allowance (RDA), one of the DRIs, is the average daily dietary intake level
that is sufficient to meet the nutrient requirements of nearly all (97-98%)
healthy individuals (2). For infants 0 to 6 months, the DRI is in the form of
an Adequate Intake (AI), which is the mean intake of zinc in healthy, breastfed
infants. The AI for zinc for infants from 0 through 6 months is 2.0 milligrams
(mg) per day. The 2001 RDAs for zinc (2) for infants 7 through 12 months, children
and adults in mg per day are:
Table 1: Recommended
Dietary Allowances for Zinc for
Infants over 7 months, Children, and Adults
Age
|
Infants and Children
|
Males
|
Females
|
Pregnancy
|
Lactation
|
7 months to 3 years
|
3 mg
|
|
|
|
|
4 to 8 years
|
5 mg
|
|
|
|
|
9 to 13 years
|
8 mg
|
|
|
|
|
14 to 18 years
|
|
11 mg
|
9 mg
|
13 mg
|
14 mg
|
19+
|
|
11 mg
|
8 mg
|
11 mg
|
12 mg
|
Results of two national surveys, the National Health and Nutrition Examination Survey (NHANES III 1988-91) (12) and the Continuing Survey of Food Intakes of Individuals (1994 CSFII) (13) indicated that most infants, children, and adults consume recommended amounts of zinc. |
When can zinc deficiency
occur?
Zinc deficiency most often occurs when zinc
intake is inadequate or poorly absorbed, when there are increased losses of
zinc from the body, or when the bodys requirement for zinc increases (14-16).
Signs of zinc deficiency include growth retardation,
hair loss, diarrhea, delayed sexual maturation and impotence, eye and skin lesions,
and loss of appetite (2). There is also evidence that weight loss, delayed healing
of wounds, taste abnormalities, and mental lethargy can occur (5, 15-19). Since
many of these symptoms are general and are associated with other medical conditions,
do not assume they are due to a zinc deficiency. It is important to consult
with a medical doctor about medical symptoms so that appropriate care can be
given.
Who
may need extra zinc?
There is no single laboratory test that
adequately measures zinc nutritional status (2,20). Medical doctors who suspect
a zinc deficiency will consider risk factors such as inadequate caloric intake,
alcoholism, digestive diseases, and symptoms such as impaired growth in infants
and children when determining a need for zinc supplementation (2). Vegetarians
may need as much as 50% more zinc than non-vegetarians because of the lower
absorption of zinc from plant foods, so it is very important for vegetarians
to include good sources of zinc in their diet (2, 21).
Maternal zinc deficiency can slow fetal growth (7). Zinc supplementation has improved growth rate in some children who demonstrate mild to moderate growth failure and who also have a zinc deficiency (22). Human milk does not provide recommended amounts of zinc for older infants between the ages of 7 months and 12 months, so breast-fed infants of this age should also consume age-appropriate foods containing zinc or be given formula containing zinc (2). Alternately, pediatricians may recommend supplemental zinc in this situation. Breastfeeding also may deplete maternal zinc stores because of the greater need for zinc during lactation (23). It is important for mothers who breast-feed to include good sources of zinc in their daily diet and for pregnant women to follow their doctors advice about taking vitamin and mineral supplements.
Low zinc status has been observed in 30% to 50% of alcoholics. Alcohol decreases the absorption of zinc and increases loss of zinc in urine. In addition, many alcoholics do not eat an acceptable variety or amount of food, so their dietary intake of zinc may be inadequate (2, 24, 25).
Diarrhea results in a loss of zinc. Individuals who have had gastrointestinal surgery or who have digestive disorders that result in malabsorption, including sprue, Crohns disease and short bowel syndrome, are at greater risk of a zinc deficiency (2, 15, 26). Individuals who experience chronic diarrhea should make sure they include sources of zinc in their daily diet (see selected table of food sources of zinc) and may benefit from zinc supplementation. A medical doctor can evaluate the need for a zinc supplement if diet alone fails to maintain normal zinc levels in these circumstances.
What are some current issues and controversies about zinc?
Zinc, infections, and wound healing
The immune system is adversely affected by even moderate degrees of zinc
deficiency. Severe zinc deficiency depresses immune function (27). Zinc is required
for the development and activation of T-lymphocytes, a kind of white blood cell
that helps fight infection (2, 28). When zinc supplements are given to individuals
with low zinc levels, the numbers of T-cell lymphocytes circulating in the blood
increase and the ability of lymphocytes to fight infection improves. Studies
show that poor, malnourished children in India, Africa, South America, and Southeast
Asia experience shorter courses of infectious diarrhea after taking zinc supplements
(29). Amounts of zinc provided in these studies ranged from 4 mg a day up to
40 mg per day and were provided in a variety of forms (zinc acetate, zinc gluconate,
or zinc sulfate) (29). Zinc supplements are often given to help heal skin ulcers
or bed sores (30), but they do not increase rates of wound healing when zinc
levels are normal.
Zinc and the common cold
The effect of zinc treatments on the severity or duration of cold symptoms
is controversial. A study of over 100 employees of the Cleveland Clinic indicated
that zinc lozenges decreased the duration of colds by one-half, although no
differences were seen in how long fevers lasted or the level of muscle aches
(31). Other researchers examined the effect of zinc supplements on cold duration
and severity in over 400 randomized subjects. In their first study, a virus
was used to induce cold symptoms. The duration of illness was significantly
lower in the group receiving zinc gluconate lozenges (providing 13.3 mg zinc)
but not in the group receiving zinc acetate lozenges (providing 5 or 11.5 mg
zinc). None of the zinc preparations affected the severity of cold symptoms
in the first 3 days of treatment. In the second study, which examined the effects
of zinc supplements on duration and severity of natural colds, no differences
were seen between individuals receiving zinc and those receiving a placebo (sugar
pill) (32). Recent research suggests that the effect of zinc may be influenced
by the ability of the specific supplement formula to deliver zinc ions to the
oral mucosa (32). Additional research is needed to determine whether zinc compounds
have any effect on the common cold.
Zinc and iron absorption
Iron deficiency anemia is considered a serious public health problem in
the world today. Iron fortification programs were developed to prevent this
deficiency, and they have been credited with improving the iron status of millions
of women, infants, and children. Some researchers have questioned the effect
of iron fortification on absorption of other nutrients, including zinc. Fortification
of foods with iron does not significantly affect zinc absorption. However, large
amounts of iron in supplements (greater than 25 mg) may decrease zinc absorption,
as can iron in solutions (2, 33). Taking iron supplements between meals will
help decrease its effect on zinc absorption (33).
What
is the health risk of too much zinc?
Zinc toxicity has been seen in both acute and
chronic forms. Intakes of 150 to 450 mg of zinc per day have been associated
with low copper status, altered iron function, reduced immune function, and
reduced levels of high-density lipoproteins (the good cholesterol) (34). One
case report cited severe nausea and vomiting within 30 minutes after the person
ingested four grams of zinc gluconate (570 mg elemental zinc) (35). In 2001
the National Academy of Sciences established tolerable upper levels (UL), the
highest intake associated with no adverse health effects, for zinc for infants,
children, and adults (2). The ULs do not apply to individuals who are receiving
zinc for medical treatment, but it is important for such individuals to be under
the care of a medical doctor who will monitor for adverse health effects. The
2001 Upper Levels for infants, children and adults are (2):
Table 2: Upper Levels for Zinc for Infants, Children, and Adults
Age
|
Infants and Children
|
Males and Females
|
Pregnancy and Lactation
|
||
0 to 6 months
|
4 mg
|
|
|
||
7 to 12 months
|
5 mg
|
|
|
||
1 to 3 years
|
7 mg
|
|
|
||
4 to 8 years
|
12 mg
|
|
|
||
9 to 13 years
|
23 mg
|
|
|
||
14 to 18 years
|
34 mg
|
|
34 mg
|
||
Ages 19+
|
|
40 mg
|
40 mg
|
Selected Food Sources
of Zinc
The 2000 Dietary Guidelines for Americans state,
Different foods contain different nutrients and other healthful substances.
No single food can supply all the nutrients in the amounts you need (36).
The following table suggests a variety of dietary sources of zinc and lists
the milligrams (mg) and percent Daily Value (%DV*) per portion. As the table
indicates, red meat, poultry, fortified breakfast cereal, some seafood, whole
grains, dry beans, and nuts provide zinc. Fortified foods including breakfast
cereals make it easier to consume the RDA for zinc, however they also make it
easier to consume too much zinc, especially if supplemental zinc is being taken.
Anyone considering taking a zinc supplement should first consider whether their
needs could be met by dietary zinc sources and from fortified foods.
If you want more information about building a healthful diet, refer to:
Dietary Guidelines for Americans
Table 3: Selected Food Sources of Zinc (9)
Search the food composition database online
at:
http://www.nal.usda.gov/fnic/etext/000020.html
Food |
Milligrams
|
%DV*
|
Oysters, battered and fried, 6 medium | 16.0 | 100 |
Ready-to-Eat (RTE) Breakfast cereal, fortified with 100% of the DV for zinc per serving, 3/4 c serving | 15.0 | 100 |
Beef shank, lean only, cooked 3 oz | 8.9 | 60 |
Beef chuck, arm pot roast, lean only, cooked, 3 oz | 7.4 | 50 |
Beef tenderloin, lean only, cooked, 3 oz | 4.8 | 30 |
Pork shoulder, arm picnic, lean only, cooked, 3 oz | 4.2 | 30 |
Beef, eye of round, lean only, cooked, 3 oz | 4.0 | 25 |
RTE Breakfast cereal, fortified with 25% of the DV for zinc per serving, 3/4 c | 3.8 | 25 |
RTE Breakfast cereal, complete wheat bran flakes, 3/4 c serving | 3.7 | 25 |
Chicken leg, meat only, roasted, 1 leg |
2.7 |
20 |
Pork tenderloin, lean only, cooked, 3 oz | 2.5 | 15 |
Pork loin, sirloin roast, lean only, cooked, 3 oz | 2.2 | 15 |
Yogurt, plain, low fat, 1 c | 2.2 | 15 |
Baked beans, canned, with pork, 1/2 c | 1.8 | 10 |
Baked beans, canned, plain or vegetarian, 1/2 c | 1.7 | 10 |
Cashews, dry roasted w/out salt, 1 oz | 1.6 | 10 |
Yogurt, fruit, low fat, 1 c | 1.6 | 10 |
Pecans, dry roasted w/out salt, 1 oz | 1.4 | 10 |
Raisin bran, 3/4 c | 1.3 | 8 |
Chickpeas, mature seeds, canned, 1/2 c | 1.3 | 8 |
Mixed nuts, dry roasted w/peanuts, w/out salt, 1 oz | 1.1 | 8 |
Cheese, Swiss, 1 oz | 1.1 | 8 |
Almonds, dry roasted, w/out salt, 1 oz | 1.0 | 6 |
Walnuts, black, dried, 1 oz | 1.0 | 6 |
Milk, fluid, any kind, 1 c | .9 | 6 |
Chicken breast, meat only, roasted, 1/2 breast with bone and skin removed | 0.9 | 6 |
Cheese, cheddar, 1 oz | 0.9 | 6 |
Cheese, mozzarella, part skim, low moisture, 1 oz | 0.9 | 6 |
Beans, kidney, California red, cooked, 1/2 c |
0.8 | 6 |
Peas, green, frozen, boiled, 1/2 c | 0.8 | 6 |
Oatmeal, instant, low sodium, 1 packet | 0.8 | 6 |
Flounder/sole, cooked, 3 oz | 0.5 | 4 |
* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains very much of a specific nutrient. The DV for zinc is 15 milligrams (mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided in one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet. |
Updated 12/9/02
Index
of dietary supplement fact sheets
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