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

Abstract

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.

Figure 1. Associations between the national prevalence of inadequate zinc intake as estimated by different nutrient composition databases.

Estimates are based on the Composite, WorldFood System International Mini-list (IML) and Nutrition Data System for Research (NDSR) nutrient composition databases. Physiological requirements developed by the International Zinc Nutrition Consultative Group (IZiNCG), the Miller equation for absorbed zinc and a 25% inter-individual CV in intake are constant across estimates. The dashed lines represent the linear regression lines and the solid line represents the line of identity (intercept = 0, slope = 1). N = 188 countries.

Figure 2. Associations between the (A) national prevalence and (B) country-specific rank order by prevalence of inadequate zinc intake as estimated by different physiological requirements.

Estimates are based on the physiological requirements developed by the International Zinc Nutrition Consultative Group (IZiNCG) and the Food and Nutrition Board of the Institute of Medicine (FNB/IOM). The composite nutrient database, the Miller equation for absorbed zinc and a 25% inter-individual CV in intake are used for all estimates. The solid line represents the line of identity (intercept = 0, slope = 1). N = 188 countries. Country rank orders were assigned in descending order, with the country with the highest estimated prevalence of inadequate zinc intake having the lowest rank.

Figure 3. Associations between the (A) national prevalence and (B) country-specific rank order by prevalence of inadequate zinc intake as estimated by different IZiNCG Zn requirements.

Estimates are based on physiological and dietary zinc requirements developed by the International Zinc Nutrition Consultative Group. The composite nutrient database and a 25% inter-individual CV in intake are used for all estimates. The solid line represents the line of identity (intercept = 0, slope = 1). N = 188 countries. Country rank orders were assigned in descending order, with the country with the highest estimated prevalence of inadequate zinc intake having the lowest rank.

Figure 4. Associations between the (A) national prevalence and (B) country-specific rank order by prevalence of inadequate zinc intake as estimated by different FNB/IOM Zn requirements.

Estimates are based on physiological and dietary zinc requirements developed by the Food and Nutrition Board of the Institute of Medicine. The composite nutrient database and a 25% inter-individual CV in intake are used for all estimates. The solid line represents the line of identity (intercept = 0, slope = 1). N = 188 countries. Country rank orders were assigned in descending order, with the country with the highest estimated prevalence of inadequate zinc intake having the lowest rank.