More people are short on iron than any other nutrient. Iron deficiency can cause anemia, a shortage of the molecules that carry oxygen in the blood. A few small studies have found that overweight children are more likely to be low on iron than normal-weight children, so researchers at the University of Rochester looked for that trend in a data set that represents the whole country.

What the researchers wanted to know: Is there any link between obesity and iron deficiency in children?

What they did: The researchers used data from NHANES III, a study of the health of Americans run by the Centers for Disease Control and Prevention between 1988 and 1994. Anyone can use the data, which comprise a 40,000-person representative sample of the U.S. population ages 2 and over. For this study, they used the data on 9,698 children and adolescents between 2 and 16 years for whom there was data on iron.

What they found: Children with higher body mass index were twice as likely as normal-weight children to be deficient in iron. Almost 10 percent of overweight 12- to 16-year-olds were iron-deficient.

What it means to you: Maybe overweight children should be watched more closely for iron deficiency.

Caveats: Because the data comes from a survey, the researchers can't say whether being overweight causes iron deficiency or whether they're both related to some other factor.

Find out more: Iron-deficiency anemia from the National Library of Medicine: http://www.nlm.nih.gov/

Read the article: Nead, K.G., et al. "Overweight Children and Adolescents: A Risk Group for Iron Deficiency." Pediatrics. July 2004, Vol. 114, No. 1, pp. 104-108.

Abstract online: http://pediatrics.aappublications.org