Zinc Zinc
NIH—Office of Dietary Supplements

Zinc Introduction

Zinc is an essential mineral that is naturally present in some foods, added to others, and available as a dietary supplement. Zinc is also found in many cold lozenges and some over-the-counter drugs sold as cold remedies.

Zinc is involved in numerous aspects of cellular metabolism. It is required for the catalytic activity of approximately 100 enzymes [1,2] and it plays a role in immune function [3,4], protein synthesis [4], wound healing [5], DNA synthesis [2,4], and cell division [4]. Zinc also supports normal growth and development during pregnancy, childhood, and adolescence [6-8] and is required for proper sense of taste and smell [9]. A daily intake of zinc is required to maintain a steady state because the body has no specialized zinc storage system [10].

Recommended Intakes

Intake recommendations for zinc and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences) [2]. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender [2], include the following:

Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals. Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy. Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects [2].

The current RDAs for zinc are listed in Table 1 [2]. For infants aged 0 to 6 months, the FNB established an AI for zinc that is equivalent to the mean intake of zinc in healthy, breastfed infants.

Table 1: Recommended Dietary Allowances (RDAs) for Zinc [2] Age Male Female Pregnancy Lactation 0–6 months 2 mg* 2 mg* 7–12 months 3 mg 3 mg 1–3 years 3 mg 3 mg 4–8 years 5 mg 5 mg 9–13 years 8 mg 8 mg 14–18 years 11 mg 9 mg 12 mg 13 mg 19+ years 11 mg 8 mg 11 mg 12 mg

* Adequate Intake (AI)

Sources of Zinc

Food
A wide variety of foods contain zinc (Table 2) [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 types of seafood (such as crab and lobster), whole grains, fortified breakfast cereals, and dairy products [2,11].

Phytates—which are present in whole-grain breads, cereals, legumes, and other foods—bind zinc and inhibit its absorption [2,12,13]. Thus, the bioavailability of zinc from grains and plant foods is lower than that from animal foods, although many grain- and plant-based foods are still good sources of zinc [2].

Table 2: Selected Food Sources of Zinc [11] Food Milligrams (mg)
per serving Percent DV* Oysters, cooked, breaded and fried, 3 ounces 74.0 493 Beef chuck roast, braised, 3 ounces 7.0 47 Crab, Alaska king, cooked, 3 ounces 6.5 43 Beef patty, broiled, 3 ounces 5.3 35 Breakfast cereal, fortified with 25% of the DV for zinc, ¾ cup serving 3.8 25 Lobster, cooked, 3 ounces 3.4 23 Pork chop, loin, cooked, 3 ounces 2.9 19 Baked beans, canned, plain or vegetarian, ½ cup 2.9 19 Chicken, dark meat, cooked, 3 ounces 2.4 16 Yogurt, fruit, low fat, 8 ounces 1.7 11 Cashews, dry roasted, 1 ounce 1.6 11 Chickpeas, cooked, ½ cup 1.3 9 Cheese, Swiss, 1 ounce 1.2 8 Oatmeal, instant, plain, prepared with water, 1 packet 1.1 7 Milk, low-fat or non fat, 1 cup 1.0 7 Almonds, dry roasted, 1 ounce 0.9 6 Kidney beans, cooked, ½ cup 0.9 6 Chicken breast, roasted, skin removed, ½ breast 0.9 6 Cheese, cheddar or mozzarella, 1 ounce 0.9 6 Peas, green, frozen, cooked, ½ cup 0.5 3 Flounder or sole, cooked, 3 ounces 0.3 2

* DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration to help consumers compare the nutrient contents of products within the context of a total diet. The DV for zinc is 15 mg for adults and children age 4 and older. Food labels, however, are not required to list zinc content unless a food has been fortified with this nutrient. Foods providing 20% or more of the DV are considered to be high sources of a nutrient.

The U.S. Department of Agriculture’s Nutrient Database Web site [11] lists the nutrient content of many foods and provides a comprehensive list of foods containing zinc.

Dietary supplements
Supplements contain several forms of zinc, including zinc gluconate, zinc sulfate, and zinc acetate. The percentage of elemental zinc varies by form. For example, approximately 23% of zinc sulfate consists of elemental zinc; thus, 220 mg of zinc sulfate contains 50 mg of elemental zinc. The elemental zinc content appears in the Supplement Facts panel on the supplement container. Research has not determined whether differences exist among forms of zinc in absorption, bioavailability, or tolerability.

In addition to standard tablets and capsules, some zinc-containing cold lozenges are labeled as dietary supplements.

Other sources
Zinc is present in several products, including some labeled as homeopathic medications, sold over the counter for the treatment and prevention of colds. Numerous case reports of anosmia (loss of the sense of smell), in some cases long-lasting or permanent, have been associated with the use of zinc-containing nasal gels or sprays [14,15]. In June 2009, the FDA warned consumers to stop using three zinc-containing intranasal products because they might cause anosmia [16]. The manufacturer recalled these products from the marketplace. Currently, these safety concerns have not been found to be associated with cold lozenges containing zinc.

Zinc is also present in some denture adhesive creams at levels ranging from 17–34 mg/g [17]. While use of these products as directed (0.5–1.5 g/day) is not of concern, chronic, excessive use can lead to zinc toxicity, resulting in copper deficiency and neurologic disease. Such toxicity has been reported in individuals who used 2 or more standard 2.4 oz tubes of denture cream per week [17,18]. Many denture creams have now been reformulated to eliminate zinc.

Zinc Intakes and Status

Most infants (especially those who are formula fed), children, and adults in the United States consume recommended amounts of zinc according to two national surveys, the 1988–1991 National Health and Nutrition Examination Survey (NHANES III) [19] and the 1994 Continuing Survey of Food Intakes of Individuals (CSFII) [20].

However, some evidence suggests that zinc intakes among older adults might be marginal. An analysis of NHANES III data found that 35%–45% of adults aged 60 years or older had zinc intakes below the estimated average requirement of 6.8 mg/day for elderly females and 9.4 mg/day for elderly males. When the investigators considered intakes from both food and dietary supplements, they found that 20%–25% of older adults still had inadequate zinc intakes [21].

Zinc intakes might also be low in older adults from the 2%–4% of U.S. households that are food insufficient (sometimes or often not having enough food) [22]. Data from NHANES III indicate that adults aged 60 years or older from food-insufficient families had lower intakes of zinc and several other nutrients and were more likely to have zinc intakes below 50% of the RDA on a given day than those from food-sufficient families [23].

Zinc Deficiency

Zinc deficiency is characterized by growth retardation, loss of appetite, and impaired immune function. In more severe cases, zinc deficiency causes hair loss, diarrhea, delayed sexual maturation, impotence, hypogonadism in males, and eye and skin lesions [2,8,24,25]. Weight loss, delayed healing of wounds, taste abnormalities, and mental lethargy can also occur [5,8,26-30]. Many of these symptoms are non-specific and often associated with other health conditions; therefore, a medical examination is necessary to ascertain whether a zinc deficiency is present.

Zinc nutritional status is difficult to measure adequately using laboratory tests [2,31,32] due to its distribution throughout the body as a component of various proteins and nucleic acids [33]. Plasma or serum zinc levels are the most commonly used indices for evaluating zinc deficiency, but these levels do not necessarily reflect cellular zinc status due to tight homeostatic control mechanisms [8]. Clinical effects of zinc deficiency can be present in the absence of abnormal laboratory indices [8]. Clinicians consider risk factors (such as inadequate caloric intake, alcoholism, and digestive diseases) and symptoms of zinc deficiency (such as impaired growth in infants and children) when determining the need for zinc supplementation [2].