[UBC is the University of British Columbia, Vancouver, British Columbia]
ADHD diagnosed in December children more often, UBC study finds
By Sharon Kirkey, Postmedia News March 5, 2012
December babies are significantly more likely than their classmates to be diagnosed with attention deficit hyperactivity disorder, a new study of nearly a million B.C. children has found.
The results suggest that some children are being put on drugs for ADHD merely because they are not as mature as older children in their class.
Published this week in the Canadian Medical Association Journal, the study found that girls born in December were 70 per cent more likely to have an ADHD diagnosis than girls born in January, while boys born in December were 30 per cent more likely to have a diagnosis of ADHD than boys born in January.
Similarly, girls were 77 per cent more likely and boys were 41 per cent more likely to be given a prescription for a medication to treat ADHD if they were born in December than if were born in January.
``Our study suggests younger, less mature children are inappropriately being labelled and treated,' said lead author Richard Morrow, of the University of British Columbia. ``It is important not to expose children to potential harms from unnecessary diagnosis and use of medications.'
Children within the same grade can be almost one year apart in age. Yet only a handful of studies - and none of them outside of the U.S. - have examined what is known as the ``relative-age' effect on the diagnosis of ADHD.
The UBC team set out to see whether the same phenomenon exists in Canada.
A total of 937,943 children were included in the study. The team included children who were aged six to 12 at any time during the study period from 1997 to 2008.
In B.C., the cut-off for entry into each year's class is a Dec. 31 birthday.
The researchers found that the youngest and least mature children within the grade were at higher risk for treatment and diagnosis of ADHD at all ages, from six to 12 - a pattern that held for the duration of the 11-year study.
``Even children born during the three days before the end of the calendar year had a higher risk than children born during the first three days of the following year, despite being born in the same season' and all within a six-day period, the authors write.
Drugs used to treat ADHD can affect a child's sleep, appetite and growth. Concerns have also been raised over whether stimulant medications such as methylphenidate (the active ingredient in Ritalin) and amphetamines increase the risk of heart attack or stroke.
In 2006, Health Canada advised Canadians not to use ADHD drugs if they have high blood pressure, heart disease or abnormalities, hardening of the arteries or an overactive thyroid gland. The Canadian Paediatric Society has recommended that all children undergo a careful history and physical examination before being started on stimulant medications to check for risk factors for sudden death.
However, a study published last month involving more than 171,000 youth aged six to 21 found no link between stimulant use and an increased risk of heart-related events in otherwise healthy young people.
ADHD is the most commonly diagnosed behavioural disorder of childhood, affecting an estimated three to seven per cent of school-age children.
In the B.C. study, the proportion of children receiving a diagnosis of ADHD increased with each birth month from January to September, for both boys and girls, then plateaued until December (the percentage of boys getting a diagnosis decreased slightly in December).
Overall, 5.7 per cent of boys born in January received an ADHD diagnosis, versus 7.4 per cent of boys born in December.
For girls, 1.6 per cent of those born in January were diagnosed with ADHD, compared to 2.7 per cent of December-born girls.
Girls are more likely than boys to be diagnosed with the ``inattentive' type of ADHD, which requires fewer symptoms to make a diagnosis and doesn't require them to be hyperactive, said co-author Dr. Jane Garland, a clinical professor of psychiatry at UBC and head of the mood and anxiety disorders clinic at B.C. Children's Hospital in Vancouver.
But younger, more immature girls in the class might appear to have excessive inattention, Garland said, when they're simply ``normal' for a younger child.
In addition to needlessly exposing children to the known side effects of ADHD drugs, ``labelling' a normal child with a disorder may affect their self-esteem as well as how they are viewed by other children and their parents, she said.
Symptoms of ADHD include fidgeting, not seeming to listen and being easily distracted - something all children do to some degree, relative to their developmental stage, Garland said.
A child's behaviour should be assessed not just inside but also outside of school, Garland said. When making a diagnosis, she says ``we need to really think carefully: How old is this child actually?'
skirkey(at)postmedia.com
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