The most studied and more prevalent nutritional problems – anaemia and iron, folate, zinc, vitamin A and iodine deficiencies – are serious public health issues that particularly affect young children and women. The most common causes of micronutrient deficiencies are related to inadequate intakes, utilization or increased losses.

Anaemia is a condition in which the number of red blood cells or the haemoglobin concentration within them is lower than normal. The most common causes of anaemia include nutritional deficiencies, particularly of iron, although deficiencies in folate, vitamin B₁₂ and vitamin A are also important causes; inherited haemoglobinopathies; and infectious diseases, such as malaria, tuberculosis, HIV and parasitic infections. Anaemia is a serious global public health problem that particularly affects young children and pregnant women. WHO estimates that 40% of children aged 6–59 months and 37% of pregnant women worldwide are anaemic (4).

Low folate status in women of reproductive age can lead to adverse health consequences of public health significance, such as megaloblastic anaemia (folate deficiency) and an increased risk of pregnancies affected by neural tube defects. A review, which involved searching eight databases and the WHO Micronutrients Database, identified surveys of population prevalence of folate deficiency or insufficiency in women of reproductive age. Between 2000 and 2014, 45 relevant surveys in 39 countries were published. Prevalence of folate deficiency was >20% in many countries with lower-income economies but was typically <5% in countries with higher-income economies. Eleven surveys reported the prevalence of folate insufficiency, which was >40% in most countries (5).

Zinc deficiency is largely related to inadequate intake or absorption of zinc from the diet, although excess losses of zinc during diarrhoea may also contribute. Severe zinc deficiency was defined in the early 1900s as a condition characterized by short stature, hypogonadism, impaired immune function, skin disorders, cognitive dysfunction, and anorexia. Estimates based on food availability data indicate that zinc inadequacy (i.e. intakes that do not satisfy the nutrient requirements) affects about one third of the world’s population, with estimates ranging from 4% to 73% across subregions. Although severe zinc deficiency is rare, mild-to-moderate zinc deficiency is quite common throughout the world. At least 17% of the world’s population is at risk of inadequate zinc intake with the highest risk occurring in sub-Saharan Africa and south Asia (6). Worldwide, it is estimated that zinc deficiency is associated with approximately 16% of lower respiratory tract infections, 18% of malaria and 10% of diarrhoeal disease.

Vitamin A deficiency is the leading cause of preventable blindness in children and increases the risk of disease and death from severe infections. In pregnant women, vitamin A deficiency causes night blindness and may increase the risk of maternal mortality. Vitamin A deficiency is a public health problem in more than half of all countries, especially in Africa and south-east Asia, affecting young children and pregnant women in low-income countries the most (7).

Emerging, unexpected situations that affect health, food safety or trade have a deep impact on micronutrient status, especially of vulnerable populations such as children, women and elderly people. The COVID-19 pandemic is likely worsening the already high prevalence of micronutrient deficiencies worldwide. Lockdowns and physical distancing may lead to decreased family income and reduced access to crops, food, services, health care and social protection programmes that could result in increased rates of malnutrition and micronutrient deficiency. Modelling predicts that the COVID-19 pandemic will have a significant impact on maternal and child undernutrition and child mortality in the current generation, with large long-term negative consequences on productivity (8).

Wheat is cultivated and consumed in many parts of the world, and its domestication contributed to the development of farming and human civilization. It was first cultivated 9000 years ago in the Euphrates Valley of the Middle East. An estimated 65% of the global wheat crop is used for human consumption, 17% is used for animal feed and 12% is used in industrial applications, including biofuel production (9). China, India and the Russian Federation are the top three producers of wheat (10). Low-income countries consume 77% of wheat produced globally and are generally wheat importers, with wheat accounting for 24% of imported food commodities in these countries (11, 12). In 2019, the annual production of wheat was 765 769 635 tonnes, being the second most produced cereal after maize and before rice (12).

Wheat is a staple in many countries due to its agronomic adaptability, ease of grain storage and milling, and suitability for making edible, palatable, acceptable and satisfying foods (13). Doughs produced from wheat flour differ from those made from other cereals in their unique viscoelastic properties. Wheat varieties, including hard/soft, winter/spring, and red, white and durum, are grown at a variety of altitudes and in various types of soil throughout the world.

All types of wheat belong to the genus Triticum aestivum, subspecies vulgare. In addition, three other species are cultivated and traded: T. durum , T. compactum and T. spelta. Because of its quality, durum wheat is used by the pasta industry, and non-durum wheat is used for milling, livestock feed or ethanol production. Wheat kernels have three components: bran, germ, and endosperm. Most wheat is milled into flour through mechanical extraction of the endosperm, the core part of the kernel containing mainly carbohydrates and some proteins (14, 15). The nutrient-rich germ and bran are usually removed in refined flours and therefore the micronutrient content of these flours is lower than that of whole wheat flour.

The production of wheat flour is a multi-step process to isolate the endosperm and subsequent sifting into flour (16). The extraction rate of a flour is the extent to which it has been sifted to separate the fine-grain endosperm, with a higher extraction rate indicating higher retention of the bran and germ. Most vitamins and minerals in wheat are found in the bran or germ, and flours of 80% or lower extraction rates have a significantly reduced micronutrient content (14). However, high-extraction flour also contains higher levels of phytates, which interfere with intestinal absorption of iron and other minerals as zinc and copper (17, 18).

Fortification is the practice of deliberately increasing the content of one or more micronutrients, i.e. vitamins and minerals, in a food to improve the nutritional quality of the food supply and provide a public health benefit with minimal risk to health. Fortification of staple foods is one of the strategies used to safely and effectively prevent vitamin and mineral inadequacies and their associated deficiencies in populations (19).

Fortification of industrially processed wheat flour, when appropriately designed and implemented, can be an efficient, simple and inexpensive strategy for supplying vitamins and minerals to the diets of large segments of the population. Industrial fortification of wheat flour has been practised for many years in several countries where the flour is used in the preparation of different types of bread and national dishes. Based on data from the Food Fortification Initiative, 86 countries in 2021 had legislation on fortification of wheat flour alone or in combination with other grains. Table 1 shows the most common levels and chemical forms of micronutrient compounds included in standards for wheat flour fortification around the world.

Decisions about which nutrients to add to fortified wheat flour and how much of each nutrient to use should be based on the nutritional needs and intake gaps of the target populations; usual level of consumption of wheat flour and products made from this staple; sensory and physical effects of the fortificant on the flour and on flour products; type of wheat and the extraction rate of the grain; availability and coverage of other fortified staple foods, in addition to other commercially available fortified products; population use of vitamin and mineral supplements; costs; feasibility; and acceptability by the producers and consumers (19–21).

Wheat flour can be fortified with several micronutrients, such as iron, folic acid and other B-complex vitamins¹, vitamin A and zinc. Some micronutrients are incorporated for restitution of original nutritional contents of unrefined wheat flour, and others are used for correcting inadequacies and their associated deficiencies of public health significance. The bioavailability of the added micronutrients will depend in part on the grain type and the extraction rate of the flour.

In many cases, procedures for the fortification of wheat and maize flours have been viewed and managed similarly, and many of the conclusions on the impact of fortification programmes are based on experiences with wheat flour, or on programmes simultaneously fortifying wheat and maize flour (22). It is now recognized that there are differences and that the principles that apply to fortification of wheat flour may not necessarily apply to fortification of other flours (23).

Table 1

Contents and chemical forms of micronutrients included in wheat fortification standards.

The whole fortification process and supply chain in a given country is an intricate network of public and private entities that link farmers, collectors, traders, millers, retailers and food processors to the final consumers. Other stakeholders include transporters; companies that supply seeds, agrochemicals, and agricultural equipment; irrigation companies; inspection agencies; government departments of commerce, tax, and agriculture; and other state agencies that control the flow in this chain according to individual governmental policies (24).

Fortification programmes should include appropriate quality-assurance and quality-control programmes at mills, as well as regulatory and public health monitoring of the nutrient content of fortified foods and assessment of the nutritional and health impacts of the fortification strategies. There are also specific country or community settings to evaluate and decisions to make. For example, from a quality-control point of view, it is desirable that milling is centralized in few mills, although this is not the case in some countries.