Type of Papers: Reports completed by expert consultations and published by the World Health Organization jointly with the Food and Agriculture Organization of the United Nations (FAO).
Note: Two WHO reports were summarized together as they contain much of the same information. See references below.
- Zinc is a component of numerous enzymes which have a variety of functions. In particular, zinc is important for enzymes involved in cell division, protein synthesis, and growth. Zinc is particularly important in the immune system and gastro-intestinal tract.
Prevalence of Deficiency:
- There is very little data on the prevalence worldwide. This is partly due to the fact that there are no reliable and widely used indicators of zinc status.
- The World Health Organization estimates that the prevalence is moderate to high in developing countries. It is estimated that 20% of the world’s population is zinc deficient (using estimates of zinc intake and bioavailability).
- Zinc deficiency is estimated to be quite common, especially in infants and children, due to the following factors:
- In several populations that have been studied, a high prevalence of low plasma zinc was found.
- Several randomized-controlled studies have found that zinc supplementation improved growth in stunted children, suggesting that these groups were zinc deficient.
- Based on the analysis of diets in children living in Kenya, Malawi, Mexico, Ghana, Guatemala, or Papua New Guinea, it was estimated that 68-94% were at risk for deficiency.
- Higher rates of zinc deficiency are found in South-East Asia (particularly Bangladesh and India), Africa, and the Western Pacific.
- It is likely that the prevalence of zinc deficiency tracks with iron deficiency as both minerals are found in the same foods (e.g., meat, poultry, and fish), and the absorption of both are affected by the presence of phytates in the diet. Iron is the most common nutrient deficiency in the world.
Risk Factors for Deficiency:
- Dietary factors:
- Low intake of animal products
- High phytate intake (phytates are found in some cereals and legumes)
- Malabsorption disorders including infection with intestinal parasites
- Diarrhea (especially persistent diarrhea)
- Genetic disorders of zinc metabolism
- There is not a clear sensitive measure for assessing zinc status. Static measures including zinc concentrations in plasma, blood cells, hair, and urine are reduced in severe zinc deficiency.
- There are limitations to each of these indicators. Concentrations may be affected by factors other than zinc status (e.g., food intake, stress and fever, and infection), and there are no clear cutoffs for all of these indicators except for plasma zinc.
- Plasma zinc concentrations may not be sufficient in detecting marginal zinc deficiencies because plasma zinc concentrations may be maintained within normal limits during a marginal deficiency.
Dietary Sources and Bioavailability:
- Best Dietary Sources:
- Lean red meat is the best source.
- Whole-grain cereals, pulses, and legumes are also good sources.
- Enhancers of zinc absorption:
- Dietary proteins reduce the negative effects of phytates (see below) on zinc absorption, thus improving zinc absorption. Animal proteins are the most effective type of protein in improving zinc absorption. Some legume-based diets (e.g., white beans, lupin proteins) are almost as effective as animal proteins in improving zinc absorption.
- Non-vegetarian/high meat diets: Approximately twice the amount of zinc is absorbed from a high meat diet compared to a diet based on rice and wheat flour.
- Inhibitors of zinc absorption:
- Phytates are chemicals found in whole grain cereals and legumes. Phytates bind zinc making it unavailable for absorption.
- Other dietary minerals such as copper, iron, or calcium have the potential to interfere with zinc absorption; however, levels of these minerals that are found in a typical diet are not high enough to affect zinc absorption. This is mainly a concern when these other minerals are consumed in large amounts such as in supplements.
- There is some evidence that high dietary calcium may further increase the negative effect of phytates, decreasing zinc absorption.
- Infant formulas: Infant formulas made from whey-adjusted cow’s milk have moderate bioavailability of zinc. Formulas made from phytate-rich vegetable proteins, such as soy, have low bioavailability (note: soy-based formulas with phytates removed can improve the bioavailability of zinc).
Recommended Nutrient Intakes (mg/day): The following are the Recommended Nutrient Intakes (RNI) as defined by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization. The RNI depends on the bioavailability of zinc (i.e., the enhancers and inhibitors of zinc absorption that are present in the diet).
(phytate-rich vegetable formula)
Upper Limits: The tolerable upper limit (UL) for zinc in children ages 1-3 years is 7 mg/day.
- Methods to improve zinc absorption:
- Reduce phytate intake in adults (it is not known if the effects of reducing phytates are the same in infants and children). The following reduces phyates in the diet:
- Use germinated cereals and legumes.
- Use fermentation (i.e., yeast) in dough for making bread.
- Include sources of animal protein (meats and fish are best, but milks also improve zinc availability).
- One study in Chinese women found that adding animal source foods to a diet based on rice and wheat approximately doubled the amount of zinc absorbed.
- Use infant formula made from whey-adjusted cow’s milk (rather than formula made from phytate-rich vegetable protein, such as soy).
- Zinc fortification:
- There is little data available on the efficacy of zinc fortification of foods. A few examples of zinc fortification include:
- In the U.S., infant formulas (with zinc sulfate), complementary foods, and ready-to eat cereals have been fortified.
- Breakfast cereals fortified with zinc oxide increased plasma zinc concentrations in children in the U.S.
- Zinc fortification of bread in Turkey improved growth rates in children who had low plasma zinc prior to fortification.
Health Consequences of Deficiency and Benefits of Intervention:
- Health Consequences of Deficiency:
- Severe zinc deficiency is associated with:
- Growth restriction (height and weight), delayed sexual and bone maturation, impaired immune functioning with recurrent infections, dermatitis and skin lesions, diarrhea, alopecia, impaired appetite (anorexia), and mental disturbance.
- The effects of mild to moderate zinc deficiency are less clear but include:
- Impaired immune functioning and reduced growth rate.
- Possibly impaired taste and wound healing.
- Infants and children are especially at risk to suffer from inadequate zinc due to zinc’s role in growth.
- Health Outcomes Associated with Interventions in Zinc Deficient Children Include:
- Improved growth in height and weight in stunted children.
- Improved immune functioning:
- Lower incidence of severe infectious diseases including malaria and acute lower respiratory tract infections.
- Lower rates of diarrhea and pneumonia (the two leading causes of child death).
- Shorter and less severe diarrhea episodes.
- A review of randomized controlled trials of zinc supplementation found:
- 18% reduction in diarrhea incidence
- 41% reduction in pneumonia incidence
Zinc. Vitamin and mineral requirements in human nutrition. Report of a joint FAO/WHO expert consultation on human vitamin and mineral requirements, Bangkok, Thailand, 21–30 September 1998. 2nd ed. Geneva: World Health Organization, 2004:230-245.