TUESDAY, May 27 (HealthDay News) -- Adults with attention deficit hyperactivity disorder (ADHD) miss, on average, more than three weeks a year in workplace productivity, according to a new global reckoning of the problem.

Altogether, between 3 percent and 4 percent of adults worldwide have ADHD, according to survey data from the World Health Organization (WHO). Researchers say the condition can cause a serious loss of concentration at work due to chronic hyperactivity, forgetfulness and impulsiveness.

But many adult workers with ADHD may not know they have a problem, the team noted.

"While surveying mental disorders around the world, we've interviewed close to 200,000 people in almost 30 countries, and we're discovering that an enormous number of adult workers -- more than 3 percent on average -- have untreated adult ADHD," said study co-author Ron Kessler, a professor of health care policy at Harvard Medical School in Boston. Kessler is also the director of the WHO's World Mental Health Survey Consortium, which is based at Harvard.

"From a societal point of view, it's a pretty big deal, because ADHD affects work performance even more than depression does," he added. "It's more persistent and severe than many mental disorders, and it results in more sick days, more accidents, and more problems interacting with colleagues. So given that employers are increasingly thinking about health care costs in terms of investment opportunities, we think it's useful to point out that it's probably a very smart and profitable business move for employers to screen their workers for ADHD and get them into treatment."

Results of the WHO survey are being published Tuesday in the online edition of the journal Occupational and Environmental Medicine.

Kessler and his colleagues conducted country-by-country ADHD diagnostic assessments on more than 7,000 employed and self-employed workers between the ages of 18 and 44.

The ADHD screenings were held in Belgium, Columbia, France, Germany, Italy, Lebanon, Mexico, the Netherlands, Spain, and the United States. All the participants were also asked to describe their work performance over the prior month.

An average of 3.5 percent of those interviewed had ADHD, a condition whose initial onset typically occurs in childhood. Among Americans, the rate rose to 4.5 percent, Kessler noted.

ADHD was more common among men than women, more common in developed than developing countries (such as Mexico, Lebanon, and Columbia), and more common among blue-collar workers than white-collar professionals. Age did not appear to be associated with ADHD risk.

Very few of the diagnosed patients said they had received any treatment for ADHD in the prior year. In fact, only some of the Dutch and American patients indicated having received any treatment for ADHD, and in those countries only about 3 percent and 13 percent of the Dutch and U.S. workers, respectively, reported any treatment history.

Those diagnosed with ADHD spent more than 22 fewer days per year working compared with non-ADHD workers. This included an average of more than eight days during which ADHD employees said they simply could not carry out their routine tasks; almost 22 days with reduced productivity; and nearly 14 days of reduced quality in the work they produced.

"The fact is that adult ADHD hasn't been on people's radar screens," said Kessler. "The feeling was that somehow magically when kids with ADHD grow up they grow out of it. But this survey shows that this is not the case."

Dr. David W. Goodman, director of the Adult Attention Deficit Disorder Center in Luthersville, Md., agreed that ADHD is an "under-diagnosed and under-recognized psychiatric condition that causes a tremendous amount of disability in the work environment."

And while he supports the idea of screening workers for ADHD, Goodman, who is also an assistant professor of psychiatry at Johns Hopkins University, worries that "identifying workers with ADHD raises the possibility for discrimination."

He also wondered whether people who are diagnosed with the condition, especially in the developing world, would have doctors available to help them.

More information

For more on ADHD and the workplace, visit the U.S. National Resource Center on ADHD.