The researchers found that preschool and school-age children who were born in August had an increased risk of being diagnosed with ADHD and receiving medication for it compared to their classmates who were born in September. Using the Taiwanese annual cut-off birthdate of August 31 for school enrollment, the researchers compared the youngest children in a grade (those born in August) with the oldest (those born in September) and assessed whether age was associated with being diagnosed with ADHD and/or being medicated. A child's age relative to his or her classmates in the same grade may have a significant impact on the diagnosis of ADHD and the prescription of ADHD medications, said Dr. Mu-Hong Chen, the study's lead author and a child and adolescent psychiatrist at Taipei Veterans General Hospital in Taiwan. Previous research on ADHD in the United States and Canada has suggested that age within a grade can make a difference in a child's risk of being diagnosed with and receiving medication for ADHD. The evidence from this new study in Taiwan showed findings that are similar to the results seen in Western countries, Chen told Live Science. When looking at the database as a whole, children born in August were more likely to be diagnosed with ADHD and/or receive ADHD medication than those born in September. Relative age within a grade may have more of an impact on younger children than on adolescents, because as age and maturity levels increase during the teenage years, the difference in neurocognitive development within a grade may decrease, he said. These findings emphasize how important it is for doctors to consider the age of a child within a grade level when they are diagnosing and prescribing medication for ADHD, Chen said.
– One's birthdate has already been linked to such things as temperament. Now researchers in Taiwan report in the Journal of Pediatrics that we can add ADHD to the list. When looking at 378,881 children ages 4 to 17 at some point between 1997 to 2011, they found that preschool and elementary school-age children born in August were 1.65 times more likely to be diagnosed with ADHD and 1.73 times more likely to be put on medication than kids born in September—who, because of school cutoff dates similar to those in the US, tend to be nearly a year older than their August counterparts. (The discrepancy did not exist in older kids, which researchers write may imply that "increasing age and maturity lessens the impact of birth month on ADHD diagnoses.") The findings add to previous work on ADHD in the US and Canada finding that a child's age within a grade plays a role in ADHD diagnosis, lead author Dr. Mu-Hong Chen tells Live Science. He calls it reduced neurocognitive maturity, something that is particularly pronounced when comparing the youngest and oldest kids within a grade. Globally, the number of kids diagnosed with ADHD has risen dramatically, researchers note in a press release, saying, "Our findings emphasize the importance of considering the age of a child within a grade when diagnosing ADHD and prescribing medication to treat ADHD." (More than one in 10 kids in the US have been diagnosed with ADHD.)