Deficiency of one or more micronutrients, particularly iron, vitamin A, zinc, and iodine, remains an intractable global health problem. Micronutrient deficiencies occur when the quantity or quality of food is chronically insufficient to meet a person’s needs.
For reasons of ethics and efficiency, it is critically important to be able to identify groups at high risk of deficiency and dietary inadequacies to effectively design health and nutrition programs that meet the needs of an affected population. However, the assessment of nutritional status and dietary intake patterns largely rely on national or small area surveys that commonly use proxy measures (e.g., anemia for iron deficiency, stunting for zinc deficiency, and dietary diversity scores for micronutrient intake), rather than the gold standard biochemical measures and multiple pass 24-hour dietary recall surveys.
While these proxy measures have been validated in many studies, large variations exist between and within countries and there is a need for more sensitive and specific data to accurately detect and estimate the extent of the nutritional problem in order to more effectively target interventions and correct deficiencies.
A new study in Plos One takes a closer look at the causes of micronutrient deficiencies among women and their children in the Democratic Republic of Congo (DRC) by estimating usual dietary intake of iron, vitamin A, and zinc, and evaluating their adequacy in relation to nutrient reference levels. Dietary intake was assessed using a multi-pass 24-hour dietary recall survey with repeat recalls in a random subsample collected among 744 Congolese mother and child pairs living in two provinces, South Kivu and Kongo Central. The overall aim of this survey was to inform the potential impact of a biofortification program in the DRC to improve micronutrient intake.
This study supports our previous biochemical findings of high levels of zinc deficiency and little to no vitamin A deficiency in this population. We observed a high prevalence of inadequate zinc intake in both provinces, ranging from 79%-86% in women and 56%-91% in children, and very low levels of vitamin A inadequacy (18% in South Kivu and 1% in Kongo Central).
Poor intake of micronutrients over time can lead to deficiencies, which can have severe and irreversible consequences for women and children. Deficiencies of iron, vitamin A and zinc contribute to high maternal and infant mortality, impaired immune and cognitive function, and stunted growth in infants and young children.
The current study is the latest in a series based on a comprehensive micronutrient survey conducted in 2014 in the DRC in which we assessed biochemical nutrition indicators, identified common inherited blood disorders associated with anemia, and estimated usual dietary patterns of women of reproductive age and their children under the age of 5.
In contrast to the zinc and vitamin A findings, our previously reported biochemical measures of iron status conflict with the dietary data: While biochemical data showed low levels of iron deficiency anemia in women and children, dietary data indicated moderate to high levels of iron inadequacy (i.e., insufficient iron intake), depending on the region and age of the child. Dietary iron inadequacy was highest in children aged 6-11 months living in South Kivu at 82%, compared to 20% among children aged 1-3 years living in Kongo Central.
These inconsistencies may be explained by the use of absorption values for iron that may not be appropriate for the Congolese diet in these two provinces. Our data shows that their diet is likely low in inhibitory factors, such as phytate and polyphenols, because of their dependency on roots and tubers as their staple foods rather than grains.
Given the low levels of iron and vitamin A deficiency, our study also explored common food sources of these nutrients. Importantly, red palm oil was identified as the primary source of vitamin A, contributing more than 70% of total vitamin A intakes in both groups and regions. This is a worrying finding, particularly given the current food system crisis in the wake of the COVID-19 pandemic. Any disruption in the supply of red palm oil could have a devastating impact on this population’s food and nutrition security and put vulnerable people at increased risk for vitamin A deficiency and morbidity. This highlights the need to diversify food sources of nutrients with other staples and non-staples rich in provitamin A carotenoids (and other essential micronutrients) such as biofortified cassava and orange sweet potato to be able to sustain nutrition and health.
Likewise, in areas in which a large proportion of the population has demonstrable risk of zinc deficiency, providing more staples and non-staples rich in zinc should be high priority. Multiple sources of minerals weave a strong safety net for rural agricultural populations. Introducing high-zinc biofortified maize into these local food systems, along with high-iron and -zinc beans and other zinc-rich crops that are culturally accepted and sustainable, should be an urgent and important priority for national agricultural research systems in similar contexts. Combining maize and beans in the correct proportions can make significant contributions to a more nutrient-dense diet—even more so if these staples are biofortified. The bioavailability of iron and zinc from beans can be enhanced through breeding the low phytate trait into local lines as well.
HarvestPlus is working with CGIAR collaborators to enhance the zinc levels in maize and to develop low phytic acid (lpa) and high-iron bean varieties for rural African and Latin American populations.
This research from the DRC demonstrates (again) that in places where anemia is not caused by iron deficiency, the scientific community must continue to insist on the need to implement more efficient surveys using nutrient-specific and accurate biomarkers.
In 2016, we reported a high prevalence of zinc deficiency and a low prevalence of biochemical iron deficiency anemia and vitamin A deficiency. In 2017, we showed that there is a high level of glucose-6 phosphatase dehydrogenase (G6PD) deficiency in Congolese children—a common inherited blood disorder in Sub-Saharan Africa can cause acute anemia—and that a commonly used biomarker for assessing anemia is not an accurate tool for detecting iron deficiency in a population with high levels of this disorder.
But many challenges exist to obtaining detailed assessments that can provide a full picture of the problem and the results of interventions. For example, to date there is no sensitive and accurate biomarker for assessment of the effect of food-based zinc interventions. Plasma or serum zinc is much more reliable as a measure of impact from medicinal or supplemental zinc interventions, particularly at the population level. Ongoing research on zinc biomarkers points to a small battery of biochemical compounds as a more sensitive option, and its validation in different age groups is also underway. In the meantime, policy makers may remain hesitant to invest in zinc interventions for which the sustainability potential is promising but the measurement of impact is less reliable.
Known epidemiological factors should also be considered for correct interpretation of biochemical results. The hemolytic anemia caused by the genetic disorder G6PD, for example, occurs almost exclusively in males; thus anemia results skewed toward males may be indicative of this or other causes at play and require specific solutions beyond iron, food, or medicine. Concurrent infections may also spuriously lead to overestimation of zinc deficiency and vitamin A deficiency (when using serum or circulating zinc and retinol levels, respectively) and underestimation of iron deficiency (when using serum or circulating ferritin) levels. Any serious evaluation of national micronutrient programs must always control for the inflammation and infection effect on these biomarkers.
Kristina Michaux is a Consultant, Nutrition Research and Knowledge Translation at HarvestPlus; Erick Boy is HarvestPlus Head of Nutrition.
Funding for this research was provided by the Bill & Melinda Gates Foundation.
