Zinc deficiency is a significant public health problem in many low- and middle-income countries (LMICs), affecting various physiological groups. Large-scale food fortification (LSFF), the addition of micronutrients to processed foods, offers a cost-effective, safe, and scalable solution to improve zinc intake and status. While 82 LMICs have mandatory LSFF standards for at least one nutrient in cereal grains, zinc is only mandated in 33. The International Zinc Nutrition Consultative Group (IZINCG) identified 35 countries with zinc deficiency as a public health problem, based on high risk of inadequate zinc intake and high stunting prevalence among children under 5 or high prevalence of low plasma/serum zinc concentration (PZC) in preschool children or women of reproductive age. This research aimed to (1) estimate country-specific prevalences of inadequate zinc intake, (2) estimate prevalences accounting for current LSFF programs, and (3) model the potential effects of improved zinc fortification programs on reducing inadequate zinc intake in countries where deficiency is a public health problem. The study utilized food balance sheet data from the Food and Agriculture Organization of the United Nations (FAO) and considered various scenarios, including full compliance with existing standards, aligning standards with current guidelines, and implementing new standards with full compliance.

The researchers reviewed existing literature on zinc deficiency in LMICs, highlighting the prevalence of low PZC in many of these nations. They also cited previous meta-analyses showing the significant impact of zinc fortification on reducing zinc deficiency. The cost-effectiveness, safety, and feasibility of LSFF through existing food systems are emphasized, contrasting it with approaches that require dietary changes or behavioral modifications. The current state of LSFF implementation globally and the variation in zinc fortification standards across countries were also reviewed. Studies on the effectiveness and barriers of zinc fortification programs in LMICs were also discussed.

The study employed a novel approach using FAO's 2018 food balance sheet data to estimate country-specific prevalences of inadequate zinc intake. These data were supplemented with information from the Global Fortification Data Exchange (GFDx) on existing LSFF programs, including fortification standards, industrial processing rates, and compliance levels. The analysis incorporated several scenarios: (1) a baseline scenario with no LSFF; (2) a 'current program' scenario reflecting existing programs and compliance; (3) a 'full compliance' scenario with 100% compliance with existing standards; (4) an 'aligned standards' scenario aligning existing standards with current international guidelines; and (5) a 'new/aligned standards with full compliance' scenario implementing new standards aligned with international guidelines and 100% compliance. The study used a composite nutrient composition database, IZINCG physiological requirements, the Miller equation for zinc absorption estimation, and a 25% inter-individual variation in zinc intake. Zinc deficiency was considered a public health problem based on the prevalence of inadequate zinc intake (>25%), stunting among children under 5 (>20%), or low PZC (>20%). Regional and global estimates were weighted by national population size. Statistical analyses were performed using SAS software.

Globally, without considering current LSFF programs, 16.4% of the population had inadequate zinc intake. This updated analysis identified 40 countries with zinc deficiency as a public health problem, primarily in South and Southeast Asia and sub-Saharan Africa. Considering current LSFF programs, the global prevalence dropped to 15% (1.13 billion individuals), with South Asia bearing the highest burden (43%). Among the 40 high-risk countries, 29 had mandatory LSFF programs, but only 17 included zinc. In these 17 countries, the existing zinc fortification programs reduced the prevalence of inadequate zinc intake by more than 10 percentage points compared to the baseline in 6 countries. However, approximately 736 million individuals in these countries still had inadequate intake. Modeling scenarios showed that: 'full compliance' with existing standards could reduce prevalence by >25% in 9 of the 17 countries; 'aligned standards' led to a >25% relative reduction in 20 of 29 countries; and 'new/aligned standards with full compliance' reduced prevalence by 78% in the 40 high-risk countries (from 736 million to 164 million), decreasing the global prevalence by approximately 50% (from 15% to 7.4%). Even with 85% compliance in the latter scenario, the reduction remained substantial (to 7.8%). Fortifying wheat flour, maize flour or rice individually demonstrated varying effectiveness by country, with wheat flour being the most effective vehicle for zinc fortification in most cases.

The findings highlight the potential of LSFF to significantly improve zinc intake in countries with public health problems. Although LSFF is a cost-effective intervention, its current implementation is suboptimal in many countries due to low compliance, inadequate zinc standards, and limited monitoring. The study provides evidence for the potential impact of improving existing programs or implementing new ones. Even incremental improvements in current programs, such as increasing compliance or aligning standards, could yield notable reductions in inadequate zinc intake. The results underscore the need for country-specific approaches, considering factors like the availability of fortifiable foods and the prevalence of at-risk populations. The model's 'ideal' scenario serves as a benchmark to inform future program design and implementation.

This study demonstrates the significant potential of large-scale food fortification programs to reduce the global prevalence of inadequate zinc intake. While various limitations exist, including uncertainties in data and modeling assumptions, the findings strongly support investments in strengthening and expanding LSFF programs that include zinc as a fortificant. Future research should focus on addressing the identified limitations, refining the models, and conducting further investigations into country-specific program implementation strategies. The study highlights the need for a multi-faceted approach to combat zinc deficiency, combining LSFF with other interventions to ensure equitable access to and benefit from fortification programs.

The study acknowledges several limitations: methodological assumptions regarding nutrient composition, zinc requirements, and absorption can influence estimates; food balance sheets might underestimate the true extent of zinc deficiency; they don't reflect actual dietary intake or intra-household disparities; the models assume 100% reach of fortifiable foods and equal consumption across all groups; the 'new/aligned standards with full compliance' scenario presents an ideal situation, potentially leading to excess zinc intake in some; and country-specific factors regarding governance and political commitment are not fully accounted for.