Global estimation of dietary micronutrient inadequacies: a modeling analysis

Original Source: The Lancet Global Health website.

Summary

Background

Inadequate micronutrient intakes and related deficiencies are a major challenge to global public health. Analyses over the past 10 years have assessed global micronutrient deficiencies and inadequate nutrient supplies, but there have been no global estimates of inadequate micronutrient intakes. We aimed to estimate the global prevalence of inadequate micronutrient intakes for 15 essential micronutrients and to identify dietary nutrient gaps in specific demographic groups and countries.

Methods

In this modelling analysis, we adopted a novel approach to estimating micronutrient intake, which accounts for the shape of a population's nutrient intake distribution and is based on dietary intake data from 31 countries. Using a globally harmonised set of age-specific and sex-specific nutrient requirements, we then applied these distributions to publicly available data from the Global Dietary Database on modelled median intakes of 15 micronutrients for 34 age–sex groups from 185 countries, to estimate the prevalence of inadequate nutrient intakes for 99·3% of the global population.

Findings

On the basis of estimates of nutrient intake from food (excluding fortification and supplementation), more than 5 billion people do not consume enough iodine (68% of the global population), vitamin E (67%), and calcium (66%). More than 4 billion people do not consume enough iron (65%), riboflavin (55%), folate (54%), and vitamin C (53%). Within the same country and age groups, estimated inadequate intakes were higher for women than for men for iodine, vitamin B12, iron, and selenium and higher for men than for women for magnesium, vitamin B6, zinc, vitamin C, vitamin A, thiamin, and niacin.

Interpretation

To our knowledge, this analysis provides the first global estimates of inadequate micronutrient intakes using dietary intake data, highlighting highly prevalent gaps across nutrients and variability by sex. These results can be used by public health practitioners to target populations in need of intervention.

Funding

The National Institutes of Health and the Dutch Ministry of Foreign Affairs.

Introduction

Micronutrient deficiencies are among the most common forms of malnutrition globally.1,2 A key pathway to micronutrient deficiencies is through inadequate intake of essential nutrients such as iron, zinc, vitamin A, iodine, and folate, among others, with deficiency in each nutrient having its own public health consequences. Iron deficiency is the most common cause of anaemia, leading to impaired cognition and adverse pregnancy outcomes.3 Vitamin A deficiency is the leading cause of preventable blindness globally, affecting mostly children and pregnant women.4 Both vitamin A and zinc have a crucial role in immunity, especially for populations facing a high burden of infectious diseases.5,6 Folate is needed early in pregnancy to reduce the risk of stillbirths and neural tube defects, and iodine is essential for pregnant and breastfeeding women because of its role in fetal and child cognitive development.7

Deficiencies in these and other micronutrients collectively contribute to a large burden of morbidity and mortality, but the scale and demographic specificities of the problem are unknown because of insufficient data.1,8 Clinical nutritional biomarkers have been used to estimate the global prevalence of micronutrient deficiencies for selected populations and micronutrients;1,4 however, substantial data gaps persist for various micronutrients, specific population groups (especially males), and many geographies. Existing data are also often outdated. The global prevalence of inadequate micronutrient supplies has been estimated using food availability data, highlighting inadequacies in food supply.9,10 Owing to scarce quantitative dietary intake data and no suitable approach with which to accurately model nutrient intake distributions, to our knowledge there have been no global estimates of inadequate micronutrient intakes. Estimates of micronutrient deficiencies, inadequate micronutrient intakes, and inadequate micronutrient supplies are all required for a comprehensive understanding of the burden of micronutrient malnutrition.

To tackle such a large-scale public health crisis, we require estimates to identify which nutrients pose the greatest risk, where, and to whom.11 Although micronutrient deficiencies are presumably widespread, data for women and children are scarce. A pooled global analysis of biomarker data found that more than one in two children younger than 5 years are deficient in either iron, zinc, or vitamin A and two in three women aged 15–49 years are deficient in either iron, zinc, or folate.1 However, we know of no global, population-wide estimates of nutrient deficiencies for a wider range of micronutrients.

Research in context

Evidence before this study

Analyses over the past 10 years have assessed global micronutrient deficiencies and global inadequate nutrient supply, but large data gaps remain for many micronutrients and population groups. Owing to limited availability of dietary intake data and a scarcity of accurate nutrient distribution data, there have been no global estimates of inadequate micronutrient intakes.

Added value of this study

This analysis provides, to our knowledge, the first global estimates to date of inadequate global micronutrient intakes using dietary intake estimates, including for specific age and sex groups and incorporating population-specific distribution data. We estimate intake inadequacies for 15 micronutrients, adding more precision than previous estimates by specifying the shape of a population's intake distribution. This study also uses publicly available data and provides all code to make these results accessible to researchers, practitioners, and the public.

Implications of all the available evidence

These findings show empirically that most of the global population has inadequate intake of at least one micronutrient. In combination with existing data on micronutrient deficiencies and supplies, estimates of inadequate global micronutrient intakes can help public health researchers and practitioners to identify which age and sex groups in which countries might be in greatest need of intervention for a wide range of micronutrients.

The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) examines the burden of micronutrient malnutrition in 195 countries using a modelling approach that combines clinical outcomes (eg, goitre), biomarkers of micronutrient status (eg, serum retinol) and anaemia (eg, haemoglobin concentration), and inadequacy in the food supply (eg, zinc inadequacy).12 These studies include estimates of disease for only four micronutrients (iodine, iron, zinc, and vitamin A) owing to scarce data;12 however, 29 micronutrients are known to be essential.13 Although GBD models might be generated using the best available methods and data, the gaps in micronutrient status biomarkers and dietary intake data hinder the ability to comprehensively model micronutrient malnutrition. Furthermore, the GBD approach to modelling micronutrient malnutrition is not replicable because the data, methods, code, and assumed nutrient distribution shapes are not publicly available.14

Although nutritional biomarkers provide the best indication of nutritional deficiencies, these deficiencies can be caused by many factors including inadequate dietary nutrient intake, infectious diseases, or absorption issues. Therefore, the best way to identify populations at risk of diet-related malnutrition is to estimate inadequate nutrient intakes. Previous studies have estimated micronutrient adequacy of the food supply.9,10,15–17 Some of these studies have used terminology to imply that these estimates reflect nutrient intakes, including “estimated prevalence of inadequate intakes”,10 “risk of inadequate intake”,10 and “apparent consumption”.18 Such terminology could have inadvertently led to confusion that global estimates of inadequate nutrient intakes already exist. However, nutrient adequacy estimates relying on food supplies do not always fully account for household food waste, food service waste, small-scale food production, or wild harvest, and they have no information on how food is allocated across each country's population (ie, there is no information for specific demographic groups, such as sex or age groups). Owing to these limitations, supply-based estimates are inaccurate, tending to underestimate inadequacy in high-income countries and overestimate inadequacy in many low-income and middle-income countries.19

In contrast to studies that rely primarily on food supplies, the Global Dietary Database (GDD) provides the only estimates of micronutrient intakes, using data from individual dietary intake surveys, household surveys, and national food supplies.20,21 The GDD standardises and compiles individual-level dietary datasets from 185 countries for more than 50 foods, beverages, and nutrients,21 providing the best available data to understand the amount of nutrients actually consumed by individuals rather than supplied. However, the GDD does not estimate micronutrient intake distributions or micronutrient requirements, which are needed to accurately estimate the prevalence of inadequate micronutrient intakes.

This Article provides a novel and reproducible approach to estimating the global prevalence of inadequate micronutrient intakes by accounting for the shapes of nutrient intake distributions and using globally harmonised nutrient reference values. We aimed to identify dietary nutrient gaps in specific demographic groups and countries, as well as estimate the total global burden of dietary micronutrient inadequacies for 15 essential micronutrients.

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