The number of overweight adolescents has doubled in the United States in the last three decades, and according to a new study there is a link between poverty and being overweight which is more discernable in the 15- to 17-year-old age group.

Study author Richard A. Miech from Johns Hopkins University in Baltimore, examined trends in adolescent overweight from 1971 to 2004 by family poverty status, as well as trends in eating and physical activity behaviors.

He says it was found that 23 percent of 15- to 17-year-olds from poor families were overweight, compared with 14 percent of non-poor in that age group, regardless of race or gender.

The figures, based on four National Health and Nutrition Examination Surveys carried out from 1971 to 2004, found the proportion of poor and non-poor children who were overweight was about the same among 12- to 14-year-olds.

Miech says that overweight children have higher risks of diabetes, high blood pressure and potentially fatal illnesses when they reach adulthood, and the fact that older children are more autonomous and free to choose what they eat and do, may explain the disparity.

The research shows that the trends of increasing overweight showed a greater impact in families living below the poverty line among older (15-17 years) adolescents.

Poorer children were significantly more likely to get more calories from soft drinks than non-poor children, were more likely to skip breakfast and less likely to engage in less physical activity.

The study is published in the Journal of the American Medical Association.