The prevalence of chronic health conditions among children in the U.S. doubled between 1994 and 2006, according to a study published in the February 17 issue of JAMA The Journal of the American Medical Association.

Harvard scientists Jeanne Van Cleave, Steven Gortmaker and James Perrin, analyzed data from the Child Cohort of the National Longitudinal Survey of Youth. Three cohorts (ranging in size from 905 to 2,337) of children ages two to eight (with an average age of four) were followed for six years each—between 1988 and 1994, 1994 and 2000, and 2000 and 2006. The prevalence of chronic conditions including obesity, asthma, behavioral and learning problems (such as attention deficit disorder and mental retardation) and physical conditions (such as heart trouble or orthopedic handicap) increased progressively over time, with end-of-study prevalence rates rising from 11.2 percent in 1994, to 25.1 percent in 2000 to 26.6 percent in 2006.

But only a small proportion of children who entered the study with a chronic condition (7.4 percent) still had it when the study finished. "Chronic conditions in childhood are common and dynamic, underscoring the benefits of continuous, comprehensive health services for all children to adjust treatment of chronic conditions, promote remission, and prevent onset of new conditions," the researchers report.

The team cites environmental changes, better survival for premature babies and the "late effects" of certain cancer treatments in mothers as possible factors contributing to the rising incidence. The prevalence was highest among male, Hispanic and black children. Maternal obesity was associated with having any chronic condition, with the strongest link to childhood obesity.

Although the results suggest that certain conditions might respond well to treatment or even resolve naturally over the course of development, having a chronic condition in childhood is a risk factor for having the same condition later, the authors report. Chronic diseases are among the "most common, costly, and preventable of all health problems in the U.S.," according to the U.S. Centers for Disease Control.

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