Iron deficiency is already recognised as a problem in obese adults, but this study is the first to examine the association in children, say the scientists behind the finding.
Lead author Xiaomian Tan, a doctoral researcher in the University of Leeds’ School of Food Science and Nutrition, said: “The relationship between undernutrition and critical micronutrients for childhood growth and development is well established, but less is known about the risk of deficiencies in iron, vitamin A, and zinc in children and adolescents who are overweight or obese, making this a hidden form of malnutrition.
“Our research is hugely important given the high prevalence of obesity in children. We hope it will lead to increased recognition of the problem by healthcare practitioners and improvements in clinical practice and care.”
Iron deficiency associated with both underweight and overweight children
The researchers examined thousands of medical studies from 44 countries involving people under the age of 25 where levels of iron and other vitamins and minerals had been recorded alongside weight.
They found that iron deficiency was associated with both underweight and overweight children and adolescents.
Zinc and vitamin A deficiencies were only observed in children who were undernourished, leading the team to conclude that iron deficiency in overweight children most probably occurs because of inflammation disrupting the mechanisms that regulate absorption of the nutrient.
The research, which was funded by the UK Biotechnology and Biological Sciences Research Council, was published in BMJ Global Health.
Iron deficiency, obesity and ‘hidden hunger’
Iron deficiency in children has a negative effect on brain function, including attention, concentration, and memory, and can increase the risk of conditions like autism and attention deficit hyperactivity disorder (ADHD).
Historically, the problem has been linked to malnutrition; it is a particular concern in lower- and middle-income countries (LMICs), where hunger can be the leading cause of mortality for young children.
Increasingly, however, it is being recognised that vitamin and mineral deficiencies can also occur in people who are overweight and obese, and who have a nutrient-poor but energy-dense diet – a phenomenon described as “hidden hunger”.
In high-income countries, obesity is linked to ultra-processed foods that are high in fat, sugar, salt, and energy – but in LMICs, it is associated with poverty and diets with limited choices of staples such as corn, wheat, rice, and potatoes.
The rapid increase in the global prevalence of obesity in recent decades, especially in children aged between five and 19 years, means that many LMICs are now facing a double burden of malnutrition alongside overnutrition.
Africa and Asia experiencing highest double burden of malnutrition
The research also drew attention to differences in focus between higher-income countries and LMICs; most studies in Africa and Asia focused on undernutrition, whereas those from North America and Europe focused entirely on overnutrition.
This is concerning given that Africa and Asia are experiencing the highest double burden of malnutrition due to economic growth and the transition to a Western-style high-sugar, high-fat diet.
Between 2000 and 2017, the number of overweight under-fives in Africa increased from 6.6 to 9.7 million; in Asia, that figure rose from 13.9 to 17.5 million. In Africa, there was also an increase in the number of stunted children under five – from 50.6 to 58.7 million.
Research supervisor Professor Bernadette Moore said: “These stark figures underscore the fact that the investigation of micronutrient deficiencies in relation to the double burden of malnutrition remains critically important for child health.
“By the age of 11 here in the UK, one in three children [is] living with overweight or obesity, and our data suggests that even in overweight children, inflammation leading to iron deficiency can be an issue.
"Iron status may be the canary in the coalmine, but the real issue is that prolonged inflammation leads to heart disease, diabetes, and fatty liver.”
Increasing physical activity and improving diet quality have been shown to reduce inflammation and improve iron status in children. The researchers are now calling for further studies into the effectiveness of these interventions.
