Study finds higher body mass index (BMI) is a risk factor for iron deficiency in children one to three years of age

New research from The Hospital for Sick Children (SickKids) has shown a higher body mass index (BMI) is a risk factor for iron deficiency in children one to three years of age. The study concludes that young children with a high BMI, indicating they are overweight or obese, should be considered for targeted screening for iron deficiency.

Iron deficiency and obesity during early childhood are common nutrition-related disorders and are linked with adverse health outcomes later in life. Since early childhood is a sensitive time for brain development and maturation, iron deficiency may lead to serious effects on the brain and subsequent developmental delays. Obesity in childhood, which may continue into adulthood, is associated with adverse cardiometabolic outcomes. This is why detecting iron deficiency is critical during the early childhood years – the peak prevalence of iron deficiency.

The association between obesity and iron deficiency has been studied before; however, there are few studies that looked at patients less than five years of age. Drs. Cory Borkhoff, Clinical Epidemiologist, Division of Paediatric Medicine at SickKids and Patricia Parkin, Research Director, Paediatric Outcomes Research Team, Division of Paediatric Medicine at SickKids, confirmed findings from a previous U.S. study using National Health and Nutrition Examination Survey (NHANES) data of children aged one to three years.

Drs. Borkhoff and Parkin and their team have studied iron deficiency in children for several years. In separate studies, they identified several risk factors for iron deficiency including the consumption of cow’s milk over 500 mL per day, breastfeeding beyond 12 to 15 months without iron supplementation, and consumption of meat or meat alternatives less than twice per day. While studying these other risk factors for iron deficiency, higher BMI was consistently identified as a statistically significant variable. This led their team to further explore the relationship between BMI and iron deficiency.

Currently, there is no iron deficiency screening recommendation in Canada. In the United States, the American Academy of Pediatrics recommends universal screening of all children at 12 months of age using a blood test that measures hemoglobin to screen for iron deficiency anemia. This is problematic because the blood test for hemoglobin detects anemia — a late stage of iron deficiency.

“As there is no screening recommendation in Canada, most Canadian children do not have any blood tests at their routine health supervision visits,” says Dr. Borkhoff, who is also an Assistant Professor in the Institute of Health Policy, Management and Evaluation, at the University of Toronto. “We are developing a clinical decision rule to help primary care physicians identify young children at risk for iron deficiency and know which children to screen for iron deficiency using a ferritin blood test.”

The team has completed derivation of a clinical decision rule, a decision-making tool that can be used to estimate the risk of iron deficiency among children aged one to three years during their regularly scheduled visit with their primary care physician. Their next step in the development of the clinical decision rule is external validation of the rule in a prospective sample of children one to three years of age.

Borkhoff and Parkin propose a two-step targeted screening process. Using a clinical decision rule that combines known risk factors to estimate the risk of iron deficiency for an individual child, health-care providers can rule out iron deficiency in young children and therefore take no further action for these low-risk children. Step two would be for those children not identified as low risk to have their iron status confirmed by a ferritin blood test. A blood test for ferritin is a test that is available in most labs, relatively non-invasive, and highly sensitive and specific in its early identification of iron deficiency. If the child’s ferritin is low, parents can discuss strategies with their child’s physician to increase iron in the diet and whether oral iron supplements may be needed.

This study was conducted within the primary care practice-based research network called The Applied Research Group for Kids (TARGet Kids!). A partnership between primary care physicians in the community and child health researchers at SickKids, St. Michael’s Hospital and McMaster University, TARGet Kids! is the only research network embedded in primary care physician offices in community settings in Canada. When young children come for their regularly scheduled visits with their paediatrician or family physician, they are invited to participate. The network recently enrolled their 10,000th child.

This work was supported by a grant from the Canadian Institutes of Health Research. Funding to support TARGet Kids! was provided by multiple sources including the Canadian Institutes for Health Research (CIHR), the SickKids Foundation and the St. Michael's Hospital Foundation.

It is an example of how SickKids is making Ontario Healthier, Wealthier and Smarter (www.healthierwealthiersmarter.com).

The study was published on Jan. 7, 2019 in the Journal of Pediatrics.