Researchers found that in 2011, an estimated 12 percent of U.S. kids aged 5 to 17 had ever been diagnosed with ADHD. That was up 43 percent from 2003.
Trends are shifting
"But what struck us the most were the increases among girls and Hispanic children," said senior researcher Sean Cleary, an associate professor of epidemiology and biostatistics at George Washington University, in Washington, D.C.
Historically, ADHD has been most often diagnosed in boys, particularly white boys. But Cleary's team found that the trends are shifting.
ADHD is still almost twice as common among white kids compared with their Hispanic peers – 14 percent versus less than 8 percent. But between 2003 and 2011, the prevalence among Hispanic children rose by 83 percent, compared with a 46 percent increase among white children, the study found.
Similarly, boys still have more than double the rate of ADHD compared to girls. But the prevalence among girls increased by 55 percent during the study period: By 2011, slightly more than 7 percent of girls had ever been diagnosed with the disorder, Cleary's team reported in the 8 December online issue of the Journal of Clinical Psychiatry.
The question is why, Cleary said.
"Have doctors been traditionally underdiagnosing this in girls and Hispanic children?" he said. "Or is this a true increase in the incidence of ADHD? Or is this overdiagnosis? We can't say."
Problems with daydreaming
It's possible, according to Cleary, that the increase among Hispanic children reflects a growing cultural acceptance of ADHD – or the wider availability of mental health resources in Spanish.
As for the increase among girls, Cleary noted that ADHD symptoms can be different for girls and boys.
Boys' symptoms are often more overt, and they may stand out as "troublemakers". With girls, attention issues seem more common – so they may have problems with daydreaming, Cleary said, or with getting schoolwork done.
"It's possible there's been a growing awareness of that over time," he said.
But Dr Andrew Adesman, a behavioural paediatrics specialist who was not involved in the study, agreed that the reasons for the findings remain unclear.
The analysis, which is based on federal government data, seems to "convincingly show that ADHD is on the rise", he said.
"But it does not help us understand why these increases are being observed," said Adesman, chief of developmental and behavioural paediatrics at Cohen Children's Medical Centre of New York, in New Hyde Park, New York.
Problems with attention and behaviour
There has long been controversy surrounding ADHD, with critics charging that some children are being labelled as having a "disease" and treated with drugs they do not need.
Ritalin and other so-called stimulant medications are often prescribed for the disorder, and some parents balk at the idea of having their child on a drug long-term.
Cleary said that if parents think their child is having significant problems with attention and behaviour, they should talk to their paediatrician: The cause may be ADHD or something different, such as sleep problems. And Adesman pointed out that this study looked at kids' lifetime prevalence of ADHD.
"Although that 12 percent figure is concerning and definitely reflects an increase in recent years, it does not mean that 12 percent of children at any one point in time have ADHD," Adesman said.