Second to iron, zinc is the most abundant trace element in the body. Zinc is found mainly in hair, bones, teeth, liver, skin, muscle, white blood cells, and the testes.
Zinc is involved in hundreds of metabolic processes; its ubiquitous role in catalyzing enzymatic reactions makes it one of the most important micronutrients in the human diet.
Worldwide, zinc deficiency due to malnutrition is relatively common; inadequate dietary zinc is the 11th major risk factor in the global distribution of disease burden. (World Health Organization. The World Health Report, 2002: Reducing Risks, Promoting Healthy Life. Geneva, Switzerland. WHO 2002)
Dietary zinc deficiency is less problematic in industrialized countries, but secondary deficiency due to impaired absorption or poor retention of zinc is relatively common.
Since measurement of serum zinc does not accurately reflect total body stores, a diagnosis of zinc deficiency is usually based upon the presence of other signs of malnutrition (low body weight, hypoalbuminemia, etc.) or of conditions commonly associated with zinc deficiency. Low tissue levels (i.e., in blood cells, hair, saliva, or nails) can aid in making the diagnosis.
Signs of Zinc Deficiency
- Growth retardation or failure to thrive in children
- Delayed puberty
- Erectile dysfunction
- Chronic diarrhea
- Hair loss
- Poor appetite
- Dermatitis
- Night blindness
- Anemia
- Impaired wound healing
- Lethargy
- Glossitis
- Nail abnormalities
- Male hypogonadism
- Decreased immune response
- Maternal deficiency may contribute to low birth weight, fetal malformations, and premature delivery
Diseases and Conditions Associated with Zinc Deficiency
- Crohn’s disease
- Chronic diarrhea
- Ulcerative colitis
- Diabetes mellitus
- Anorexia nervosa
- Celiac disease
- Chronic alcoholism
- Sickle cell disease
- Cirrhosis
- Acrodermatitis enteropathica (a rare genetic disorder that causes zinc malabsorption)
- Prior intestinal surgery (gastric bypass, small bowel resection, etc.)
- Short-bowel syndrome
- Pregnancy and lactation
- Strict vegan diet
- Prolonged intravenous feeding
(From King J, Cousins R. Zinc. In: Shils M, et al, eds. Modern Nutrition in Health and Disease. 10th ed. Baltimore: Lippincott Williams & Wilkins; 2006:271-285 and The Merck Manual, 18th Edition. Zinc. 2006:55-56)
Supplementation with Zinc
Much of the benefit that is attributed to routine zinc supplementation may be due to repletion of subclinical deficiencies, rather than any independent effect of zinc. However, when a bona fide deficiency exists—and for some specific conditions—zinc supplementation is necessary or “possibly helpful”:
- Mild zinc deficiency is treated with two to three times the recommended daily allowance (RDA), while more severe deficiencies are treated with four to five times the RDA for up to six months.
- Malnourished children with acute diarrhea benefit from up to 20 mg of zinc daily.
- Age-related macular degeneration may be slowed by a combination of 80 mg zinc, 2 mg copper, 500 mg vitamin C, 400 IU vitamin E, and 15 mg beta-carotene daily.
Under conditions of adequate nutrition, the RDA for zinc varies with age:
- 0-6 months: 2 mg
- 7 months to three years: 3 mg
- Four to eight years: 5 mg
- Nine to 13 years: 8 mg
- Over 14 years: 11 mg (men); 8 mg (women)
- During pregnancy and lactation, the RDA for zinc is 11 mg and 12 mg, respectively.
Ongoing supplementation up to the tolerable upper intake level (40 mg daily in adults) is safe, but chronic ingestion of high doses can lead to copper deficiency, anemia, impaired immunity, GI side effects, an increased risk of advanced prostate cancer in men, and other complications.
Iron and phytates (found in grains and legumes) interfere with zinc absorption and should be ingested at least two hours apart from zinc supplements.
(From Saper R, Rash R. Zinc: an essential micronutrient. Am Fam Phys. 2009;79(9):768-772)
