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BALTIMORE -- Children with attention deficit-hyperactivity disorder (ADHD) had a higher chance of having a short stature by the fourth grade, especially if they were on medication, researchers said here.

From kindergarten to fourth grade, kids with diagnosed ADHD had almost four times the odds of having a short stature (height <3rd percentile) versus kids without ADHD (odds ratio 3.88, 95% CI 1.69-8.88, P<0.01) after adjusting for sex, parental education, and family income, reported Ladan Davallow Ghajar, MD, of the University of Virginia in Charlottesville, and colleagues.

Compared with children without ADHD, those who did have the disorder demonstrated significantly lower height-for-age z scores (HAZ) from kindergarten to fourth grade (difference 0.26, 95% CI 0.08-0.44, P<0.01) and lower BMI z scores (BMIZ) across the same period (difference 0.28, 95% CI 0.07-0.50, P<0.01), Ghajar said at the Pediatric Academic Societies (PAS) annual meeting.

"Given the negative effect of ADHD and its treatment on growth, we should ensure we educate parents about the risk of poor growth in children with ADHD with or without treatment," she said.

Among the 699 children with ADHD in this study, a longer duration of ADHD medication use was also associated with lower HAZ (β -0.187, P<0.0001) and BMIZ (β -0.154, P<0.0001), compared to children who were not on medication, Ghajar reported.

It remains unclear whether the poor growth observed in this study was an isolated childhood event, or whether it persisted in adulthood, as the children in this cohort have not been followed-up past early adolescence, noted PAS session moderator Lisa Swartz Topor, MD, of Brown University, in Providence, Rhode Island.

"But it does tell us that we need to study our ADHD children, with and without treatment, and look at their growth trajectories to see how tall they are as adults," Swartz Topor told MedPage Today, adding that the findings are particularly relevant because of the large numbers in the adolescent population diagnosed with ADHD.

A 1998 study suggested that ADHD may be associated with in height gain through mid-adolescence that may normalize by late adolescence, and that they appeared to be mediated by ADHD and not by its treatment.

Ghajar highlighted a that found neither ADHD, nor ADHD stimulant treatment, were associated with a child's final adult height. However, this study did find a positive correlation in males between a longer duration of stimulant use before peak height velocity and the age at which they reached their peak height velocity, which could be explained by a "maturational lag," researchers said.

"The mechanism by which ADHD itself affects growth is not known, but one hypothesis is ... maturational lag, where it's hypothesized that children with ADHD have delays in development, but then have improved symptoms over time due to maturational catch up with increasing age," she said.

Ghajar said the link between ADHD medication use and increased risk for poor growth could be explained by symptoms of the medication, such as a diminished appetite. Stimulant medications such as Adderall or Ritalin have also been shown to increase synaptic dopamine, which inhibits the growth hormone, she said.

The current study used data from the cohort, in which children's growth charts were evaluated in kindergarten, second grade, and fourth grade for changes in HAZ and BMIZ. Researchers conducted telephone interviews with parents to determine if their child had been diagnosed with ADHD, and if they responded affirmatively, they were asked whether they were taking medication for ADHD.

Of the 7,603 children evaluated, 3% had been diagnosed with ADHD in kindergarten, 3.7% in second grade, and 4.2% in fourth grade. By fourth grade, 77% of kids were on medication for their ADHD, as were 79% of children in second grade, and 12% of kindergarteners.

Overall, Ghajar noted that the difference in HAZ scores between children with and without ADHD was equivalent to about a 1.5-cm (less than 1 in) height difference, whereas the difference in BMIZ equated to about a 11 percentile points difference.

Lastly, children who were diagnosed with ADHD by kindergarten grew at a slower rate from kindergarten through fourth grade than other children who were diagnosed later, with lower HAZ scores (β=0.23, 95% CI 0.04-0.42, P<0.05), and less BMI gain (β=0.16, 95% CI 0.03-0.29, P<0.05), Ghajar reported.

Study limitations include the fact that the researchers were unable to collect information on the number or type of medication (stimulant vs non-stimulant) used by children diagnosed with ADHD, and the lack of information on hormone levels and parental height data in the study sample.

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