People who work too much may be more likely to have ADHD or depression, according to a new study from Norway.

Researchers found that, among the workaholics in the study, nearly 33 percent had symptoms of ADHD, compared with about 13 percent of non-workaholics. For the study, workaholics were defined as those who met seven criteria, including whether they work so much that it has negatively influenced their health, or they feel stressed when they are prohibited from working.

"Workaholics scored higher on all the psychiatric symptoms than non-workaholics," Cecilie Schou Andreassen, a clinical psychologist at the University of Bergen in Norway, said in a statement.

For example, nearly 26 percent of workaholics had symptoms of obsessive-compulsive disorder (OCD), compared with about 9 percent among non-workaholics.

Moreover, about 34 percent of workaholics had symptoms of anxiety, compared with 12 percent of non-workaholics.

And nearly 9 percent of workaholics had symptoms of depression, compared with 2.6 percent of non-workaholics, according to the study, published May 18 in the journal PLOS ONE. [7 Ways Depression Differs in Men and Women]

The results show that "taking work to the extreme may be a sign of deeper psychological or emotional issues," Schou Andreassen said. But the study looked at people at just one point in time, so it cannot say whether working too much may lead to mental health problems, or whether having mental health problems may lead to working too much, or whether some other factor could lead to both.

It also isn't clear what mechanism could be behind the potential link, the researchers said. "Whether this reflects overlapping genetic vulnerabilities, disorders leading to workaholism or, conversely, workaholism causing such disorders, remains uncertain," Schou Andreassen said.

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For example, researchers speculated that people with ADHD might have to work harder and longer to compensate for possible issues caused by their condition. But it is also possible that their disorder makes them more likely to take on projects and tasks impulsively, which may result in taking on more work than they can realistically do during regular working hours.

As for the link between workaholism, anxiety and depression, working a lot might serve as an escape mechanism from negative feelings, the researchers speculated. But it could also be that people with anxiety may fear failing and therefore go over their work several times, which forces them to work longer. And people with depression may work more slowly due to their low energy levels and therefore have to compensate by working longer hours, the researchers said in their study.

In the study, researchers asked 16,426 people in Norway to rate how often during the past year they thought about how they might free up time to do more work, how often they worked to reduce negative feelings such as guilt or anxiety, and much more time they spent working than they initially intended. [9 DIY Ways to Improve Your Mental Health]

Based on the answers, the researchers found that 1,287 (nearly 8 percent) in the study were workaholics.

When the researchers took a closer look at their data, they found that workaholism was linked to certain personal characteristics. People who were younger, single, highly educated and of a higher economic status showed greater levels of workaholism than people without these characteristics, the researchers found.

Workaholism was also more common among women, managers, self-employed people and people working in the private sector, the researchers found.

It should not be assumed that people who are successful at work do not have mental health problems, the researchers said.

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