The research is important given the rising numbers of obese children around the world. More than 20 per cent of European children are overweight and 9 per cent are obese, according to Datamonitor figures. This is set to rise to 25 per cent and 11 per cent respectively in 2008.
While iron deficiency is more commonly associated with the developing world, it remains the leading nutrient deficiency in the UK. A lack of iron can in the worst cases cause anaemia but even a small deficiency can lead to learning and behavioral problems, as underlined in recent studies.
The new study, published in this month's Pediatrics (vol. 114, no. 1, pp. 104-108), analysed data from almost 10,000 children aged two to 16 years old. Among these 13.7 per cent were at risk for overweight and 10.2 per cent were overweight.
Overall, the prevalence of iron deficiency increased as body mass index increased, said the researchers, and iron deficiency was particularly common among adolescents (nearly one in 10).
In a multivariate regression analysis, children who were at risk for overweight and children who were overweight were approximately twice as likely to be iron-deficient as were those who were not overweight.
The association between iron deficiency and being overweight may be caused by lack of exercise or a diet lacking in iron-rich foods, the study said. It also said that genetics could play a role, and that overweight girls tend to grow faster than their peers, making it difficult for them to keep up with their bodies' iron requirements.