Estimating the global prevalence of inadequate zinc intake from national food balance sheets: effects of methodological assumptions

Background

The prevalence of inadequate zinc intake in a population can be estimated by comparing the zinc content of the food supply with the population’s theoretical requirement for zinc. However, assumptions regarding the nutrient composition of foods, zinc requirements, and zinc absorption may affect prevalence estimates. These analyses were conducted to: (1) evaluate the effect of varying methodological assumptions on country-specific estimates of the prevalence of dietary zinc inadequacy and (2) generate a model considered to provide the best estimates.

Methodology and Principal Findings

National food balance data were obtained from the Food and Agriculture Organization of the United Nations. Zinc and phytate contents of these foods were estimated from three nutrient composition databases. Zinc absorption was predicted using a mathematical model (Miller equation). Theoretical mean daily per capita physiological and dietary requirements for zinc were calculated using recommendations from the Food and Nutrition Board of the Institute of Medicine and the International Zinc Nutrition Consultative Group. The estimated global prevalence of inadequate zinc intake varied between 12–66%, depending on which methodological assumptions were applied. However, country-specific rank order of the estimated prevalence of inadequate intake was conserved across all models (r = 0.57–0.99, P<0.01). A “best-estimate” model, comprised of zinc and phytate data from a composite nutrient database and IZiNCG physiological requirements for absorbed zinc, estimated the global prevalence of inadequate zinc intake to be 17.3%.

Conclusions and Significance

Given the multiple sources of uncertainty in this method, caution must be taken in the interpretation of the estimated prevalence figures. However, the results of all models indicate that inadequate zinc intake may be fairly common globally. Inferences regarding the relative likelihood of zinc deficiency as a public health problem in different countries can be drawn based on the country-specific rank order of estimated prevalence of inadequate zinc intake.

Estimating the global prevalence of zinc deficiency: results based on zinc availability in national food supplies and the prevalence of stunting

Background

Adequate zinc nutrition is essential for adequate growth, immunocompetence and neurobehavioral development, but limited information on population zinc status hinders the expansion of interventions to control zinc deficiency. The present analyses were conducted to: (1) estimate the country-specific prevalence of inadequate zinc intake; and (2) investigate relationships between country-specific estimated prevalence of dietary zinc inadequacy and dietary patterns and stunting prevalence.

Methodology and Principal Findings

National food balance sheet data were obtained from the Food and Agriculture Organization of the United Nations. Country-specific estimated prevalence of inadequate zinc intake were calculated based on the estimated absorbable zinc content of the national food supply, International Zinc Nutrition Consultative Group estimated physiological requirements for absorbed zinc, and demographic data obtained from United Nations estimates. Stunting data were obtained from a recent systematic analysis based on World Health Organization growth standards. An estimated 17.3% of the world’s population is at risk of inadequate zinc intake. Country-specific estimated prevalence of inadequate zinc intake was negatively correlated with the total energy and zinc contents of the national food supply and the percent of zinc obtained from animal source foods, and positively correlated with the phytate: zinc molar ratio of the food supply. The estimated prevalence of inadequate zinc intake was correlated with the prevalence of stunting (low height-for-age) in children under five years of age (r = 0.48, P<0.001).

Conclusions and Significance

These results, which indicate that inadequate dietary zinc intake may be fairly common, particularly in Sub-Saharan Africa and South Asia, allow inter-country comparisons regarding the relative likelihood of zinc deficiency as a public health problem. Data from these analyses should be used to determine the need for direct biochemical and dietary assessments of population zinc status, as part of nationally representative nutritional surveys targeting countries estimated to be at high risk.

Estimating the global prevalence of zinc deficiency: results based on zinc availability in national food supplies and the prevalence of stunting

BACKGROUND

Adequate zinc nutrition is essential for adequate growth, immunocompetence and neurobehavioral development, but limited information on population zinc status hinders the expansion of interventions to control zinc deficiency. The present analyses were conducted to: (1) estimate the country-specific prevalence of inadequate zinc intake; and (2) investigate relationships between country-specific estimated prevalence of dietary zinc inadequacy and dietary patterns and stunting prevalence.

METHODOLOGY AND PRINCIPAL FINDINGS

National food balance sheet data were obtained from the Food and Agriculture Organization of the United Nations. Country-specific estimated prevalence of inadequate zinc intake were calculated based on the estimated absorbable zinc content of the national food supply, International Zinc Nutrition Consultative Group estimated physiological requirements for absorbed zinc, and demographic data obtained from United Nations estimates. Stunting data were obtained from a recent systematic analysis based on World Health Organization growth standards. An estimated 17.3% of the world's population is at risk of inadequate zinc intake. Country-specific estimated prevalence of inadequate zinc intake was negatively correlated with the total energy and zinc contents of the national food supply and the percent of zinc obtained from animal source foods, and positively correlated with the phytate: zinc molar ratio of the food supply. The estimated prevalence of inadequate zinc intake was correlated with the prevalence of stunting (low height-for-age) in children under five years of age (r = 0.48, P<0.001).

CONCLUSIONS AND SIGNIFICANCE

These results, which indicate that inadequate dietary zinc intake may be fairly common, particularly in Sub-Saharan Africa and South Asia, allow inter-country comparisons regarding the relative likelihood of zinc deficiency as a public health problem. Data from these analyses should be used to determine the need for direct biochemical and dietary assessments of population zinc status, as part of nationally representative nutritional surveys targeting countries estimated to be at high risk.

Short-term zinc supplementation with dispersible tablets or zinc sulfate solution yields similar positive effects on plasma zinc concentration of young children in Burkina Faso: a randomized controlled trial

OBJECTIVE

To assess zinc absorption from dispersible tablets by investigating the effects of short-term zinc supplementation, provided either as zinc (Zn) sulfate dispersible tablets or solution, on changes in plasma Zn concentration in young children.

STUDY DESIGN

We conducted a randomized, partially-masked, placebo-controlled trial in 451 children 6 to 23 months of age in Burkina Faso, randomly assigned to receive a dispersible tablet containing 5 mg Zn, a Zn solution containing 5 mg Zn/5 mL, or a placebo solution, daily for 3 weeks. The main outcome measure was change in plasma zinc concentration after supplementation compared with baseline.

RESULTS

The mean plus or minus SD change in plasma Zn concentration (μg/dL) was significantly greater in both Zn supplemented groups (tablets: 16.9±13.1μg/dL, liquid: 16.6±14.2 μg/dL), compared with the placebo group (0.2±10.9 μg/dL; P<.001, ANOVA). In both Zn supplemented groups, but not in the placebo group, change in plasma Zn concentration was progressively less with increasing age in months (-0.79 μg/dL/mo and -1.15 μg/dL/mo, respectively; P<.001); this effect did not differ in the Zn supplemented groups (P=.18).

CONCLUSIONS

Short-term supplementation results in a large increase in plasma Zn concentration, regardless of whether the additional Zn is provided as a dispersible tablet or solution.

Plasma zinc concentration responds rapidly to the initiation and discontinuation of short-term zinc supplementation in healthy men

To assist with the evaluation of zinc (Zn) intervention programs, information is needed on the magnitude and velocity of response of plasma Zn concentration following changes in Zn intake. Our objective in this study was to measure plasma Zn concentration of healthy adult men before and after initiation and discontinuation of 1 of 2 dosages of Zn supplements or placebo. We conducted a randomized, double-blind, placebo-controlled trial in 58 apparently healthy males aged 19-54 y. Participants received 1 of 3 liquid supplements daily for 21 d: 10 or 20 mg Zn/d, as Zn sulfate, or placebo. Fasting plasma Zn concentrations were measured on 14 occasions before, during, and after supplementation. Data were analyzed using mixed-model ANCOVA. The plasma Zn concentration was related to day of study (P < 0.0001) and study group (P < 0.0001). Controlling for baseline concentrations, plasma Zn concentrations were consistently elevated above baseline by d 5 among individuals in both of the Zn-supplemented groups compared with those receiving placebo supplements, regardless of their initial plasma Zn concentration. There were no significant group-wise differences between those who received either 10 or 20 mg/d Zn. Plasma Zn concentrations of supplemented individuals declined following withdrawal of supplementation and within 2 wk no longer differed from those of the placebo group. Change in the plasma Zn concentration is a useful indicator to monitor compliance with, and possibly effectiveness of, Zn supplementation programs. To ensure accurate interpretation of the results, samples should be collected while the intervention is still in progress.

Zinc bioavailability from zinc-fortified foods

Zinc fortification is considered a potentially useful strategy for the control of zinc deficiency, but the success of such intervention programs depends on the population's access to and consumption of zinc-fortified foods and adequate absorption of zinc from these foods. The latter issue has been assessed by a variety of studies that applied zinc isotopic tracers to assess zinc uptake from zinc-fortified foods. These studies show that the additional zinc provided by zinc fortification decreases fractional absorption of zinc, but increases total zinc absorption from these foods. Available studies show no significant difference in zinc absorption from foods fortified with either zinc oxide or zinc sulfate, which are the two cheapest chemical forms of zinc that are generally recognized as safe for human consumption. It appears that high-phytate meals depress zinc absorption from zinc-fortified foods, although total zinc absorption from such foods is still likely to be greater than if the foods were not fortified with zinc. With the possible exception of Na2EDTA, putative enhancers of zinc absorption do not seem to confer major benefits for zinc absorption from zinc-fortified foods. There is little information on the effect of fortification with other micronutrients on zinc absorption from co-fortified foods, and zinc fortification does not seem to suppress iron absorption from iron-fortified foods in most studies.