Overweight children are at double the risk of being iron deficient, perhaps because of bad diet or lack of exercise, a study said on Tuesday.

Iron deficiency is a global problem most commonly found in poorer people lacking proper nutrition, but the study concluded that the rising number of obese people in the developed world should be checked and treated for it.

Too little iron in the blood can cause anemia and lead to learning and behavioral problems as well as pose limits on work and exercise.

One out of seven U.S. children is overweight, a three-fold increase in the past 30 years, and many do not get screened for iron deficiency, Yale University researcher Karen Nead wrote in the journal Pediatrics.

In her study of 10,000 children aged 2 to 16, nearly one in 10 of the overweight teenagers was iron deficient. Among 2- to 5-year-olds, 6 percent were iron deficient.

Overall, the rate of iron deficiency was double among overweight children compared to normal-weight children and was more likely the higher the children’s body mass index, a ratio of weight to height known as BMI.

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.