What is it?
Zinc has been known
for more than 50 years to be an essential mineral. It is found in almost every
cell in the body and is contained within more than 200 enzymes, substances needed
for biochemical reactions. Zinc is important for a healthy immune system , for
healing cuts and wounds , and for maintaining your sense of taste and smell. Zinc
also supports normal growth and development during pregnancy, childhood, and adolescence.
foods provide zinc?
poultry provide the majority of zinc in the American diet. Other
food sources include beans, nuts, and dairy products. Oysters
are the food containing the most zinc by weight, but beef is a
more common source in the U.S. diet. The zinc found in meat and
oysters is easily absorbed by the body. Dietary phytates, which
are found in whole grain cereals and unleavened bread, may significantly
decrease the body's absorption of zinc. The table
of food sources of zinc suggests many dietary sources
is the Recommended Dietary Allowance for zinc?
Recommended Dietary Allowance (RDA) is the average daily dietary
intake level that is sufficient to meet the nutrient requirements
of nearly all (97 - 98%) individuals in each life-stage and gender
group." The 1989 RDAs for zinc for adults, in milligrams
of two national surveys, the National Health and Nutrition Examination
Survey (NHANES III 1988-91) and the Continuing Survey of Food
Intakes of Individuals (1994 CSFII) indicated that the diets of
many adults, especially older Americans and women, do not provide
the recommended amounts of zinc.
16 mg (second
can zinc deficiency occur?
can occur when zinc intake is inadequate, when there are increased
losses of zinc from the body, or when the body's requirement for
zinc increases. There is no specific deficiency disease associated
with zinc. Instead, many general signs of zinc deficiency
can appear, including poor appetite, weight loss, delayed healing
of wounds, taste abnormalities, and mental lethargy. As body stores
of zinc decline, these symptoms worsen and are accompanied by
diarrhea, hair loss, recurrent infection, and a form of dermatitis,
a skin disorder. Zinc deficiency has also been linked to poor
growth in childhood.
may need extra zinc?
no single laboratory test available to determine zinc nutritional
status. Instead, dietary intake is typically used to estimate
the risk of a zinc deficiency. People who may benefit from a zinc
supplement include those who do not consume enough calories, vegetarians,
the elderly, pregnant and lactating women, and people who suffer
from alcoholism or digestive diseases that cause diarrhea.
a low caloric intake is at higher risk for having a low zinc intake
and for developing a zinc deficiency. Vegetarians who consume
a variety of legumes and nuts will probably meet their zinc requirement,
but otherwise a vegetarian diet may be inadequate in zinc. Since
the zinc from plant sources is absorbed less readily, this increases
the concern about zinc status in vegetarians who do not consume
legumes and nuts.
surveys suggest that many Americans aged 51 and older, pregnant
women and breastfeeding mothers do not consume recommended amounts
to decrease their risk for developing a zinc deficiency, it is
important for individuals in these groups to include sources of
zinc in their daily diet (see table of food sources
of zinc. Zinc supplementation has been found to improve the
growth rate in children with mild zinc deficiency and mild to
moderate growth failure. Maternal zinc deficiency can delay fetal
growth, and mothers who give birth to small for gestational age
babies have been found to have lower zinc intakes during pregnancy.
Breastfeeding increases the risk of depleting nutritional zinc
status when dietary zinc intake is chronically low because of
the greater need for zinc during lactation.
is frequently associated with alcoholism, which is often due to
a lower intake of food. The need for a supplement as part of an
overall treatment plan is usually evaluated by a physician in
causes a loss of zinc. Therefore, digestive diseases or gastrointestinal
surgery that result in diarrhea are often associated with zinc
deficiency. Individuals who experience chronic diarrhea should
make sure they include sources of zinc in their daily diet (see
table of food sources of zinc). A medical
doctor can evaluate the need for a zinc supplement if diet alone
fails to maintain normal zinc levels in the body.
are some current issues and controversies about zinc?
infections, and wound healing
immune system is adversely affected by even moderate degrees of
zinc deficiency. People who are zinc-deficient have a more difficult
time resisting infections. T-cell lymphocytes, white blood cells
that help fight infection, do not function efficiently when zinc
stores are low. 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.
Zinc supplements are often used to treat skin ulcers or bed sores
, but they do not increase rates of wound healing when zinc levels
and the common cold
study of over 100 employees of the Cleveland Clinic indicated
that zinc lozenges decreased the duration of colds by one-half.
Some of the participants reported fewer days of congestion and
nasal drainage, but no differences were seen in how long their
fevers lasted or in the level of muscle aches they experienced.
However, this study has been criticized by some researchers who
believe that since zinc lozenges often have a bad taste, the participants
may have known the difference between the supplement and placebo,
which would compromise the results. Also, since other studies
have shown no benefit the debate continues on the true value of
zinc supplements for cold symptoms.
and iron absorption
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, however, have raised concern about the effects of
iron fortification on other nutrients, including zinc. Iron taken
in solution can inhibit the absorption of zinc, but foods fortified
with iron do not.
is the health risk of too much zinc?
health risk of taking too much zinc is moderate to high. 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).
One case report cited severe nausea and vomiting within 30 minutes
after the person ingested four grams of zinc gluconate (570 mg
elemental zinc). The 1989 RDA committee stated that "chronic
ingestion of zinc supplements exceeding 15 mg/day is not recommended
without adequate medical supervision." The National Academy
of Sciences is currently reviewing recent research and considering
new recommendations on zinc intake and risk.
of Food Sources of Zinc (7)
shank, lean only, cooked 3 oz
chuck, lean only, cooked, 3 oz
tenderloin, lean only, cooked, 3 oz
shoulder, lean only, cooked, 3 oz
tenderloin, lean only, cooked, 3 oz
leg, cooked, 3 oz
beans, canned, 1/2 c
dry roasted w/out salt, 1 oz
dry roasted w/out salt, 1 oz
bran, 1 oz
dry roasted, unblanched,
w/out salt, 1 oz
mature seeds, canned, 1/2 c
nuts, dry roasted w/peanuts, w/out
salt, 1 oz
breast, cooked, 3 oz
muffin, 1 medium
black, dried, 1 oz
beans, 1/2 c cooked
cheddar, 1 oz
green, boiled, 1/2 c
instant, 1 packet
cooked, 3 oz
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 magnesium 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 by one serving. Even foods that provide lower percentages of the
DV will contribute to a healthful diet.