Mandatory large-scale food fortification programmes can reduce the estimated prevalence of inadequate zinc intake by up to 50% globally

Many low- and middle-income countries (LMICs) face substantial risk of zinc deficiency, with national surveys indicating high prevalence of low plasma/serum zinc concentrations (PZC) in multiple settings. Large-scale food fortification (LSFF)—the post-harvest addition of micronutrients to industrially processed foods—has been shown to improve zinc intake and status and is cost-effective, safe, and leverages existing food systems. Despite 82 LMICs having mandatory LSFF standards for at least one cereal grain as of August 2022, zinc is mandated in only 33. The International Zinc Nutrition Consultative Group (IZINCG) identified countries where zinc deficiency is a public health problem based on dietary supply risks, stunting levels, and PZC data. This study aimed to: (1) estimate country-specific prevalences of inadequate zinc intake using FAO food balance sheet data without accounting for LSFF (baseline), (2) estimate prevalences accounting for current LSFF implementations, and (3) model potential impacts of improving existing LSFF programmes or establishing new ones—including adding zinc, aligning standards with international guidelines, and increasing compliance—on inadequate zinc intake in countries where zinc deficiency is a public health problem.

Prior evidence indicates LSFF improves micronutrient intake and status in LMICs. A meta-analysis reported zinc fortification reduces zinc deficiency by 24–55%. LSFF is generally cost-effective and safe, deliverable via existing food systems, and does not require behavior change. However, zinc is frequently absent from national LSFF standards, and existing zinc standards often fall below international guidelines. Monitoring and compliance are common challenges, and limited population zinc status data hinder programme design and implementation.

Data sources and estimation approach: The analysis used 2018 FAO food balance sheets (FBS) for average daily per capita availability of food commodities (kcal per capita per day), a composite nutrient composition database for zinc and phytate contents (accounting for processing/extraction), IZINCG physiological requirements to compute mean per capita absorbed zinc requirements by age–sex structure, and the Miller saturation model to estimate absorbable zinc from dietary zinc and phytate. An inter-individual coefficient of variation of 25% was assumed to estimate the prevalence of inadequate intake using an Estimated Average Requirement cut-point-like method. LSFF programme data: The Global Fortification Data Exchange (GFDx) provided country-level presence/absence of mandatory or voluntary fortification for wheat flour, maize flour, and rice; whether zinc is included and at what standard (mg/kg); the percentage of each staple that is industrially processed; and current compliance. Zinc standards (mg/kg) were converted to mg/kcal for compatibility with FBS-based caloric availability. Where compliance data were missing for mandatory programmes, median compliance for countries on the same continent with mandatory standards for the commodity was used; compliance for voluntary standards without data was assumed zero. Calculation of LSFF zinc contribution: Additional extrinsic zinc from LSFF was computed as per-capita caloric availability (kcal/d) of each fortified commodity × zinc standard (mg/kcal) × percent industrial processing × percent compliance. Total daily zinc and phytate supplies were updated accordingly before absorption modeling. Identification of public health problem countries: LMICs were classified as having zinc deficiency as a public health problem if either (1) baseline prevalence of inadequate zinc intake >25% and under-5 stunting >20%, or (2) nationally representative PZC prevalence ≥20% in preschool children or women of reproductive age. Modeled scenarios (Table 1): - Baseline: No current LSFF considered; used to identify problem countries. - Current programme: Existing country-specific standards and compliance incorporated. - Full compliance: Current standards retained; compliance raised to 100% where mandatory standards exist; otherwise same as current. - Aligned standards: In countries with mandatory standards, add zinc if absent or align zinc levels to current guidelines based on per-capita consumption and extraction rates; compliance unchanged. Others same as current. - New/aligned standards with full compliance: Apply guideline-consistent zinc standards to wheat flour, maize flour, and rice (modeled separately and combined) with 100% compliance in all problem countries; also a sensitivity analysis at 85% compliance. Regional/global estimates applied modeled scenarios only to problem countries; elsewhere the current programme scenario was used. Analyses used population-weighted estimates across 174 countries (SAS 9.4).

- Global baseline (no LSFF): 16.4% of the world population estimated to have inadequate zinc intake. - Current programmes: Accounting for existing LSFF implementation, 15.0% globally (1.13 billion people) have inadequate zinc intake; 43% of these reside in South Asia. Regional current prevalence ranges from 6% in southern and tropical Latin America to 27% in South Asia. - Countries identified: 40 countries met public health problem criteria—18 by dietary supply plus stunting, 18 by PZC ≥20% in children or women, and 4 by all three indicators. - Existing zinc fortification: 29/40 countries have mandatory LSFF for at least one cereal; only 17 include zinc. Zinc standards vary widely (7.5–101.3 mg/kg), often below guidelines. Median industrial processing among these 17: wheat flour 100% (IQR 71.5–100%), maize flour 35% (IQR 7.5–42.5%). Median compliance: wheat 71.2% (IQR 20.0–86.0%), maize 40.0% (IQR 5.5–77.5%). - Impact of current zinc programmes: In 6 of the 17 countries with mandatory zinc fortification, current implementation reduced inadequate intake by >10 percentage points from baseline; only 4/17 remained >25% inadequate intake; by contrast, 13/23 countries without mandatory zinc standards remained >25%. - Full compliance scenario: Median compliance across programmes was 65% (IQR 9.3–84%). Raising to 100% yielded >25% relative reductions vs current in 9 countries; only Burundi and Guatemala remained >25%. However, global prevalence fell only from 15.0% to 14.5%, with ~698 million still inadequate in the 40 problem countries. - Aligned standards scenario: Adding zinc where absent or aligning levels to guidelines (compliance unchanged) produced >25% relative reductions in 20 of 29 countries with existing programmes; only Burundi and Chad remained >25%. About 646 million in problem countries would still be inadequate; global prevalence ~13.8%. - New/aligned standards with full compliance (all three staples): In the 40 problem countries, inadequate intake fell 78% from 736 million to 164 million; only Chad remained >25%. Global prevalence dropped by about half, from 15.0% to 7.4% (85% compliance sensitivity: 7.8%). - Single-vehicle full compliance (guideline levels): If only one staple per country were fortified, only two countries would remain >25%; the most effective vehicle would be wheat flour in 14 countries, maize flour in 13, and rice in 13.

The study demonstrates that LSFF, particularly when zinc is included at guideline-aligned levels with high compliance, can substantially reduce the estimated prevalence of inadequate zinc intake. Despite expansion of LSFF in LMICs, global risk has changed little in the past decade; strengthening programmes to include zinc, align standards with international guidance, and ensure compliance could halve global inadequacy. Country-specific impacts vary with the proportion of industrially processed staples and per-capita availability of fortifiable vehicles. Barriers include limited zinc status data, absence of national policies or regional standards including zinc, suboptimal zinc levels in standards, and weak monitoring/compliance systems. Even without full redesign, immediate opportunities exist: for countries already fortifying, improving compliance or aligning standards can reduce inadequacy by roughly 30%; adding zinc where mandated programmes exclude it could reduce inadequacy by ~65% without changing compliance. LSFF should be complemented by other strategies (supplementation, home fortification, biofortification) where industrially processed cereal reach is low or for vulnerable groups. Governance, regulatory monitoring, and processor capacity are essential to realize LSFF’s potential.

Using publicly available national food supply data integrated with fortification programme parameters, the study quantifies that comprehensive, high-quality mandatory LSFF of wheat flour, maize flour, and rice with zinc at guideline levels and high compliance could reduce the global prevalence of inadequate zinc intake by up to 50% and decrease inadequacy by 78% in the 40 highest-risk countries. Immediate, pragmatic steps—adding zinc to existing standards, aligning zinc levels with guidelines, and strengthening compliance—offer substantial, near-term benefits. Future priorities include expanding nationally representative zinc status (PZC) surveillance to refine targeting, ensuring equitable coverage among vulnerable groups, optimizing vehicle choice and fortification levels to local consumption patterns, and integrating LSFF with complementary interventions. Continued investment in governance, regulatory monitoring, and technical capacity will be critical to maximize impact and sustainability.

- Methodological assumptions: Estimates depend on nutrient composition databases, zinc requirement values, and absorption modeling (Miller equation); different assumptions yield divergent prevalence estimates. - Data sources identify different countries: FBS-based inadequacy, stunting, and PZC surveys do not always converge; FBS likely underestimates true zinc deficiency relative to biochemical surveys. - FBS reflect availability, not intake: They do not capture individual-level consumption, intra-/inter-household variation, or subnational disparities. - Coverage assumptions: Models assume 100% reach among consumers of industrially processed staples, ignoring inequities in access and consumption; vulnerable groups may be underreached by LSFF. - Programme feasibility: The ‘new/aligned with full compliance’ scenario is an idealized upper bound; may be infeasible or not cost-effective everywhere and could risk excessive intake in some subgroups, though current zinc ULs are debated. - Compliance data gaps: Missing compliance values were imputed using medians; voluntary programme compliance assumed zero, introducing uncertainty.