Long seen as a problem for children, attention deficit hyperactivity disorder was first described in 1845 by Dr. Heinrich Hoffman, who wrote "The Story of Fidgety Philip."
More recently, it has been recognized as continuing into adulthood for some people, and new research seeks to estimate the effect of ADHD on workers.
This lack of ability to concentrate costs the average adult sufferer 22.1 days of "role performance," per year, including 8.7 extra days absent, according to researchers led by Dr. Ron de Graaf of the Netherlands Institute of Mental Health and Addiction.
It might be cost-effective for employers to screen workers for ADHD and provide treatment, the researchers suggest.
"There were many more people than most of us who have done these studies had expected," that were affected by adult ADHD, said Dr. Ronald C. Kessler of Harvard University, a co-author of the report. "People don't come for treatment for this ... it's kind of one of those hidden things," he said in a telephone interview.
"It's an enormous impairment," Kessler said, citing absences, accidents and low performance on the job.
Kessler said he had worked with workers suffering depression and found that treatment costing $1,000 could help prevent $4,000 in lost productivity.
"It sure looks like the effect would be as big, if not bigger, for ADHD," he said. "We're looking around for an employer or two who might be willing to give this a try."
Linda S. Anderson, president of the Adult Attention Deficit Disorder Association, said workplace assistance and treatment can be vital,
Most people think of ADHD as a children's problem, but when it continues into adulthood people have a problem coping with the workplace and need assistance, said Anderson, who was not part of the research team.
The new study may underestimate the adult rate of ADHD, she said, noting that many victims may not have jobs. Those who do often struggle to keep up, but there are treatments available, she said.
The majority of the lost performance was associated with reductions in quantity and quality of work rather than actual absenteeism, the researchers said.
Many employers assume occasional absences are part of the cost of doing business, but the paper noted that, "typically they expect their workers to be working when they are on the job."
To find that most of the ADHD-related loss occurs on days when the worker is present is both striking and disturbing from an employer perspective, the authors said.
Researchers interviewed 7,075 workers aged 18 to 44 in 10 countries, concluding that an average of 3.5 percent had ADHD. Their findings are published in Tuesday's online edition of the journal Occupational and Environmental Medicine.
In 2006, a study led by Kessler estimated that 4.4 percent of adults aged 18 to 44 in the United States experience ADHD symptoms and some disability.
The new research estimated the U.S. rate at 4.5 percent among workers, costing an average of 28.3 days performance.
The highest rate was for France, 6.3 percent, but the lost time was lower at 20.1 days.
Other countries studied and ADHD rates among adults, and estimated days lost per affected worker, were Lebanon, 0.9 percent, 19.4 days; Spain, 1.3 percent, 1.1 days; Colombia, 1.9 percent, 29.4 days; Mexico, 2.4 percent, 6.1 days; Italy, 3.4 percent, 22.2 days; Germany, 3.5 percent, 13.6 days; Belgium, 3.7 percent, 16.5 days; Netherlands, 4.9 percent, performance improved.
The researchers were unable to explain why the ADHD affected workers in the Netherlands had improved performance rather than the declines seen in every other country studied.
"We periodically find one of those blips, we just don't know why," Kessler said.
In a separate study issued earlier this month, researchers led by Kessler reported that major mental disorders cost the U.S. at least $193 billion annually in lost earnings alone. That study was published in the American Journal of Psychiatry.
The new international study was supported by the World Health Organization, U.S. National Institute of Mental Health, John D. and Catharine T. MacArthur Foundation, the Pfizer Foundation, U.S. Public Health Service, Fogarty International Center, Pan American Health Organization, Eli Lilly and Company, Ortho-McNeil Pharmaceutical Inc., GlaxoSmithKline and Bristol-Myers Squibb Company.