The study is the first to discover a link between obesity and low iron levels in preschoolers. Iron deficiency can cause mental and behavioral delays, so the findings underscore the importance of healthy eating habits in children ages 1 to 3.
The researchers found that 20 percent of obese toddlers have iron deficiency, compared to 7 percent of normal-weight toddlers. Lack of iron reduces the amount of oxygen carried through the body by the blood and can cause anemia.
Experts blamed parents who let toddlers drink cow's milk and juice from a bottle, instead of weaning them and introducing iron-rich foods such as meat, beans, eggs, spinach and fortified breads.
Toddlers still fed from bottles tend to drink too much milk and juice, which are low in iron, and don't get enough solid food, said Dr. Jane Brotanek of the University of Texas Southwestern Medical Center in Dallas, a study co-author.
"What you put in your baby's bottle can affect your child's future," she said.
The researchers also found that children who attend day care centers are about 50 percent less likely to have iron deficiency than children who aren't in day care. Day care providers may pay more attention to nutrition, Brotanek speculated.
Hispanic toddlers were more likely than white and black toddlers to be obese and not in day care, possibly explaining their increased risk of iron deficiency, Brotanek said. Twelve percent of Hispanic toddlers were iron deficient, compared to 6 percent of white children and 6 percent of black children.
The study appears in the September issue of the journal Pediatrics.