Zinc

Zinc is in every cell in the body. It is a cofactor (a substance that binds with an enzyme and allows the enzyme to do its job) for nearly 100 enzymes. Zinc is involved in:

• Wound healing
• Bone formation
• DNA synthesis
• Protein, carbohydrate, and fat metabolism
• Development of sexual organs
• General tissue growth and maintenance
• Taste perception
• Acid-base balance
• Vitamin A activity
• Protection of cell membranes from free-radical attacks
• Storage and release of insulin

The effect of zinc treatments on the severity or duration of cold symptoms is inconclusive. 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. Additional research is needed to determine whether zinc compounds have any effect on the common cold.

Protein-containing foods are all good sources of zinc, particularly shellfish (especially oysters), meat, and poultry (see Table 7-7). Legumes, dairy foods, whole grains, and fortified cereals are good sources as well. Zinc is much more readily available, or absorbed better, from animal foods. Like iron, zinc is more likely to be absorbed when animal sources are eaten and when the body needs it. Only about 40 percent of the zinc we eat is absorbed into the body. Phytates, which are found in whole-grain breads, cereals, legumes, and other foods, can decrease zinc absorption.

Deficiencies are more likely to show up in pregnant women, the young, and the elderly. Adults deficient in zinc may have symptoms such as poor appetite, diarrhea, skin rash, and hair loss. Signs of severe deficiency in children include growth retardation, delayed sexual maturation, decreased sense of taste, poor appetite, delayed wound healing, and immune deficiencies. Marginal deficiencies do occur in the United States.

Zinc toxicity has been shown in both acute and chronic forms. Intakes of 150 to 450 milligrams 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). The Tolerable Upper Intake Level for adults is 40 milligrams. Since zinc supplements can be fatal at lower levels than many of the other trace minerals, zinc supplements should be avoided unless a physician prescribes them.

Food Sources of Zinc 

Food	Milligrams	% Daily Value
Oysters, battered, fried, 6 pieces	15.0	100
Breakfast cereal, fortified with 100% of the DV for zinc per serving, 3/4 cup	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	45
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
Breakfast cereal, fortified with 25% of the DV for zinc, 3/4 cup	3.7	25
Breakfast cereal, complete wheat bran flakes, 3/4 cup	3.7	25
Chicken leg, meat only, roasted, 1 leg	2.7	0
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 cup	2.2	15
Baked beans, 1/2 cup	1.7	10
Cashews, dry-roasted without salt, 1 oz.	1.6	10
Yogurt, fruit, low fat, 1 cup	1.6	10
Pecans, dry-roasted without salt, 1 oz.	1.4	10
Raisin bran, 3/4 cup	1.3	8
Chickpeas, canned, 1/2 cup	1.3	8
Mixed nuts, dry-roasted with peanuts, no salt, 1 oz.	1.1	8
Cheese, Swiss, 1 oz.	1.1	8
Almonds, dry-roasted, without salt, 1 oz.	1.0	6
Walnuts, black, dried, 1 oz.	1.0	6
Milk, fluid, any kind, 1 cup	1.0	6
Chicken breast, meat only, roasted, 1/2 breast	0.9	6
Cheese, cheddar, 1 oz.	0.9	6
Cheese, mozzarella, part-skim, low-moisture, 1 oz.	0.9	6
Beans, kidney, cooked, 1/2 cup	0.8	6
Peas, green, frozen, boiled, 1/2 cup	0.8	6
Oatmeal, instant, low-sodium, 1 packet	0.8	6
Flounder/sole, cooked, 3 oz,	0.5	4
Source: Facts About Dietary Supplements. Office of Dietary Supplements, National Institutes of Health. 2001.