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Facts About Zinc
Zinc,
infections, and wound healing
Zinc and the
common cold
Zinc and iron
absorption
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 body’s 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 doctor’s 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, Crohn’s 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
Food
Guide Pyramid
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.
|
| Who provides
this information? |
| The
Warren Grant Magnuson Clinical Center and Office of Dietary Supplements
are components of the National Institutes of Health. The Clinical Center
is the clinical research hospital for NIH. Through clinical research,
physicians and scientists translate laboratory discoveries into better
treatments, therapies and interventions to improve the nation's
health.The mission of Office of Dietary Supplements is to strengthen
knowledge and understanding of dietary supplements by evaluating
scientific information, stimulating and supporting research,
disseminating research results, and educating the public to foster an
enhanced quality of life and health for the U.S. population. |
| |
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