About 4 billion people globally suffer from vitamin and mineral deficiencies, or ‘hidden hunger’. Micronutrient deficiencies (MNDs) are especially prevalent in sub-Saharan Africa (SSA) where women and children are at the greatest risk (1–3). Even mild to moderate MNDs lead to impaired physical and cognitive development, increased morbidity from infectious diseases in infants and young children, and decreased work productivity in adulthood (4). Mineral micronutrient deficiencies (MMNDs) responsible for the largest public health burdens include iron, iodine, and zinc (5). Selenium  deficiency is emerging as a growing public health problem.

Magnitude of selenium deficiency 

Selenium is a component of enzymes that play a key role in the regulation of thyroid hormone metabolism, antioxidant defense systems, and oxidative metabolism (6). However, up to one in seven people worldwide are estimated to have low dietary selenium intake (7), and approximately 0.5 to 1 billion people are selenium deficient (8).

The situation is particularly dire in SSA (9), and has been implicated as a potential causal factor of growth faltering in children (10), and fertility impairments in women (6). Zimbabwe has a high prevalence of MNDs affecting more than 50 % of the population (11). A pilot study in three rural districts in Zimbabwe indicates that 96 % of children aged 6-59 months and 70 % of women of reproductive age have sub-optimal selenium levels (12). The high and widespread selenium deficiency among women and children in these districts is alarming and potentially of public health concern. 

Dietary selenium supply

‘Populations are what they eat’. Selenium is found mostly in diets rich in meat and meat products (13).  Across SSA, diets are predominantly crop-based and it is these sources that provide the majority of dietary selenium (14).  In many parts of Africa, staples are crops and rural diets are frequently monotonous, consisting mainly of starchy foods such as grains, tubers, and roots but with limited or negligible intake of animal-source foods (15), mainly because of economic, cultural, and religious constraints. In Zimbabwe, maize is the staple crop with an estimated production of over two million metric tonnes (16). While maize provides sustenance for many, it contributes to MNDs, including selenium deficiency (17). Maize production for consumption increases the risk of selenium deficiency in women of reproductive age in rural Zimbabwe (18). Agronomic biofortification of staple crops like maize with selenium has the potential to increase selenium concentration. Supplementation during food processing could also help close the gap.

Agriculture and selenium supply

‘Agricultural produce can only be as good as the soil it is derived from’. Selenium is consumed primarily from plant and animal sources, and since both plants and animals derive their selenium from soils; soil types are a primary driver of human selenium levels (19). Unfortunately, many soils in Zimbabwe have sub-optimal selenium concentrations (20) which is due to the prevalence of acidic soils that exhibit poor nutrient retention (21). Selenium deficiency is widespread in rural Zimbabwe where a large proportion of dietary intake is met through subsistence production and locally based food purchases. This low soil selenium translates directly into poor nutrition for the population. 

The Murewa district in rural Zimbabwe, whose dominant source of livelihood is crop production, is marred with poor selenium levels in both children and women (18). Boosting selenium levels through diverse agricultural practices is considered a means to enhance food diversity at the household level, particularly in developing countries where subsistence farming is common (22).

The distribution of selenium deficiency

Selenium deficiency isn’t evenly spread across the globe, or even within a country. The selenium levels of populations vary with geological, geochemical, and climatic factors.  All things are related, but near things are more related than distant things. Selenium concentrations of human biomarkers in rural Zimbabwe are  homogenous within districts and showed greater variation between districts.  Selenium deficiency and toxicity can occur in areas a short distance apart (7). Knowledge of the prevalence and distribution of selenium deficiency is key in determining selenium-related health risks. Selenium deficiency risk in children 6-59 months and women of reproductive age in three rural districts of  Zimbabwe was high and showed strong geographic dependency within short-range distances of approximately 12km (12). Hot spot analysis and mapping of nutrient deficiencies is essential for geographically targeted health interventions particularly; important in resource-limited settings like Zimbabwe. Spot maps are also useful in tracing the geospatial variations in Se status. 

Equity and selenium status

‘Standing on even ground’. Disparities exist in the selenium levels of males and females owing to sexual dimorphic regulation of selenium metabolism. Selenium is concentrated in male gonads (23). In rural Zimbabwe female children had an increased risk of selenium deficiency to male children (18). Addressing this disparity might require a gender-sensitive approaching selenium supplementation, as seen in growth monitoring, where growth charts target individual sexes. Multiple micronutrient powders targeted for girls can be formulated to contain higher selenium concentrations relative to boys.

Intergenerational transmission of selenium deficiency

‘The apple does not fall far from the tree’. Maternal selenium deficiency was positively associated with childhood selenium deficiency in rural Zimbabwe. Selenium is vital  for female reproductive health and its deficiency during pregnancy and lactation influences nutrition outcomes in children (24). Zimbabwe’s high breastfeeding rates exceed the global average. A lower prevalence of selenium deficiency in younger children and a higher prevalence in older children among selenium-deficient mothers validated the protective effect of breastfeeding in rural Zimbabwe (18).

The next steps 

Future research should take a holistic examination of soil, crop, dietary selenium concentrations, and human selenium levels to clearly define the agriculture, nutrition, and health linkages at scale. 

About the research

“Translating GeoNutrition (TGN): Reducing mineral micronutrient deficiencies (MMNDs) in Zimbabwe. A research collaboration between the University of Zimbabwe and the University of Nottingham with funding from the UK Research and Innovation (UKRI) Global Challenges Research Fund (GCRF) [grant number EP/T015667/1 and supported in part by Bill & Melinda Gates Foundation grant INV-009129 through the GeoNutrition project.

About the author

Dr. Beaula Mutonhodza is a researcher and lecturer within the Department of Nutrition, Dietetics and Food Sciences, University of Zimbabwe. Passionate about public health nutrition with vast experience in nutrition programming within the humanitarian sector.

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