NEW YORK (Reuters Health) - Even without classic risk factors for type 2 diabetes, people with high-stress, low-control jobs were over 60 percent more likely to develop the disease than unstressed workers in a new German study.
The findings add to substantial evidence that job strain represents a serious health risk on its own, researchers say.
"What we first suspected was that job strain might be related to lifestyle variables - that people who are under high job strain would smoke or maybe eat unhealthy food more, but this was not the case," said lead study author Karl-Heinz Ladwig, of the Technical University in Munich.
"For me this was the most exciting thing, to find out that these things might not responsible for this unique effect," he said.
Past research dating back decades has established that jobs with a combination of high demands and low control over how the work is done offer a formula for high worker stress.
That particular kind of job strain has long been linked to heart disease and death. The underlying cause is generally thought to be a mixture of physical wear-and-tear from the chronic stress itself and unhealthy coping behaviors like smoking, drinking and overeating.
A few studies in more recent years have connected this form of worker stress to diabetes, although sometimes the effect was seen only in women (see Reuters Health article of January 4, 2010, here: reut.rs/1ohWKsl) or was largely linked to coping behaviors.
To explore the connection further, Ladwig's team followed more than 5,000 men and women in Germany for over 12 years.
None of the participants had diabetes at the beginning of the study, when each answered a well-established questionnaire to measure job strain. It included 11 questions, some of which focused on job demands, such as having to work fast, hard, under time pressure or with conflicting demands, or having excessive amounts of work.
Other questions were meant to assess the person's level of job control, including their level of responsibility and competence for the job and ability to make decisions in their current position.
Based on the answers, participants were subdivided into groups: low job strain, high job strain, passive and active.
Participants with demanding jobs who had control over how their work got done, or those with undemanding jobs, were considered to have "low job strain." Those with high job demands and low control over their work were considered to have "high job strain."
Apart from job demands, people in jobs that afforded some control were considered "active" and those without control were categorized as "passive."
Almost 300 cases of type 2 diabetes developed during the follow-up period, and the largest proportion of these, almost 7 percent, came from the high job-strain group, the study team reports in the journal Psychosomatic Medicine.
The passive or active categories contributed the next largest number of cases, followed by the low job strain group, with 4 percent.
The researchers calculated that the high job strain participants had a 63 percent higher chance of developing diabetes than the low job strain group.
The results held after the team accounted for age, sex, family history of diabetes and weight. The difference did shrink somewhat when researchers factored in socioeconomic status and physical intensity of work, but remained significant.
In general, the participants with high job strain were more often female, physically inactive, smoked and had low education levels. But none of these variables made a difference in the diabetes risk based on job strain.
That suggests the stress itself is causing the effect, Ladwig and his team speculate, and the likely culprit is the stress hormone cortisol, which can alter the way the body regulates blood sugar.
"The rising prevalence of type 2 diabetes is a worldwide concern and this study is investigating the role of job strain in this growing epidemic," said Mikaela von Bonsdorff, a gerontology researcher at the University of Jyväskylä in Finland, who was not involved in the study.
The American Diabetes Association says that by 2050, one in every three Americans will have diabetes
Von Bonsdorff cautions that although the authors found high job strain might increase the risk of type 2 diabetes, it is evident that other factors such as, socioeconomic position and unhealthy living habits may be playing a role.
Loretta Platts, a researcher at Kings College London who also was not involved in the study, said, "It is also possible that the real influence of stressful work on type 2 diabetes might be even larger than is suggested by the results found in this study."
"The investigators could only measure work stress at one time-point, and it is likely to be the cumulative impact of work stress over individuals' whole working lives which may affect their chances of developing type 2 diabetes, not necessarily stress happening at any specific time-point," she said.
"People are very engaged in their job situation and they have no distance from it and I think that we should get into a balanced life situation where working is one part which is important but not the only important thing in the world," said Ladwig.
