This effect of peer social support on the risk of mortality was most pronounced among those between the ages of 38 and 43. Yet similar support from workers' supervisors had no effect on mortality, the researchers found.

In addition, men who felt like they had control and decision authority at work also experienced this "protective effect," according to the study, published in the May issue of the APA journal Health Psychology. However, control and decision authority increased the risk of mortality among women in the sample.

"[P]eer social support, which could represent how well a participant is socially integrated in his or her employment context, is a potent predictor of the risk of all causes of mortality," the researchers wrote. "An additional (unexpected) finding … is that the effect of control on mortality risk was positive for the men but negative for the women."

The researchers rated peer social support as being high if participants reported that their co-workers were helpful in solving problems and that they were friendly. Control and decision authority were rated high if participants said they were able to use their initiative and had opportunities to decide how best to use their skills, and were free to make decisions on how to accomplish the tasks assigned to them and what to do in their jobs.

The researchers, at Tel Aviv University, looked at the medical records of 820 adults who were followed for 20 years, from 1988 to 2008. The workers were drawn from people who had been referred to an HMO's screening center in Israel for routine examinations. (People who were referred because of suspected physical or mental health problems were excluded from the sample). The workers came from some of Israel's largest firms in finance, insurance, public utilities, health care and manufacturing. They reported working on average 8.8 hours a day. One-third of them were women; 80 percent were married with children; and 45 percent had at least 12 years of formal education.

The researchers controlled for the physiological, behavioral and psychological risk factors of total cholesterol, triglycerides, glucose levels, blood pressure, body mass index, alcohol consumption, smoking, depressive symptoms, anxiety and past hospitalizations. They obtained the data on the control variables from each person's periodic health examinations, including tests of physiological risk factors and a questionnaire completed during the examinations by all participants.

In addition, participants were administered another questionnaire that measured job demands, control at work and peer and supervisor support. During the 20-year follow-up period, 53 participants died.

Asked why workplace control was positive for men but not women, the lead researcher, Arie Shirom, PhD, said that for employees in blue-collar type of jobs (and most respondents belonged to this category), high levels of control were found in jobs typically held by men, rather than jobs typically held by women. "Providing partial support to our finding, a past study found that for women in blue-collar jobs, having low levels of control does not increase their risk of becoming ill with stress-related disorders," Shirom said.

One limitation of the study was that the researchers did not have data on changes in workload, control or support during the 20-year period. "Still, we argue that other researchers have consistently found that the job characteristics of workload, control and support tend to be stable across time," Shirom said.

The American Psychological Association, in Washington, D.C., is the largest scientific and professional organization representing psychology in the United States and is the world's largest association of psychologists. APA's membership includes more than 154,000 researchers, educators, clinicians, consultants and students. Through its divisions in 54 subfields of psychology and affiliations with 60 state, territorial and Canadian provincial associations, APA works to advance psychology as a science, as a profession and as a means of promoting health, education and human welfare.

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