JOB STRESS NOT RELATED TO CANCER 

There is no link between work-related stress and several common cancer types, according to a meta-analysis published online February 7 in BMJ.

An international team of researchers, led by Katriina Heikkilä, PhD, from the Finnish Institute of Occupational Health in Helsinki, found that it is unlikely that job stress is a risk factor for colorectal, lung, breast, or prostate cancer, and it is not associated with an overall risk for cancer (hazard ratio [HR], 0.97).

The researchers note that approximately 90% of cancers have been linked to environment and lifestyle, but evidence of associations with other factors, including psychosocial ones, is tentative. However, it is possible that one psychosocial factor — stress — plays a role in the development of cancer.

The physiological stress response is characterized by the secretion of more hypothalamic and pituitary stress hormones, the researchers explain. These stress biomarkers trigger and maintain chronic inflammation, which has been shown to play a role in the promotion and progression of cancer.

Work and work-related factors are sources of stress for many people, explained Dr. Heikkilä. Of course, work can also be beneficial to a person's well being.

"We used a well-known, validated, harmonized measure of work stress, called job strain, which is defined as high demands and low control over work, and found that this measure is not associated with cancer risk," she told Medscape Medical News. There are a number of possible reasons for this.

One could be related to the duration of exposure to work stress, she pointed out. "It is not known how long a person needs to be exposed to stress for it to be harmful to health, but one would think that longer exposure would be worse than shorter," she said.

"In our study, work-related stress was measured at one point in time; thus, some of the participants had been exposed to stress for longer than others," Dr. Heikkilä said. "It would be interesting to [determine] whether the duration of stress exposure is relevant to the risk for cancer or other diseases," she noted.

It might be that work-related stress alone is not sufficient to contribute to cancer development, and that a combination of stressful factors (such as stress from adverse life events and caregiver stress) is needed, Dr. Heikkilä explained.

"It is also possible that stress — at work or elsewhere — is related to the risk for some rarer types of cancer, which we did not investigate in our study," she added.

Not Related to Job Strain

To ascertain whether work-related psychosocial stress is associated with the risk for cancer, Dr. Heikkilä and colleagues conducted a meta-analysis of harmonized data from 12 independent prospective European studies. The studies were conducted in Denmark, Finland, France, the Netherlands, Sweden, and the United Kingdom from 1985 to 2008, and involved more than 116,000 participants.

All of the studies analyzed were part of the individual-participant-data meta-analysis in working populations (IPD)-Work consortium. The consortium consisted of a predefined 2-stage data-acquisition protocol. In the first stage, work stress, sociodemographic, and lifestyle baseline data were harmonized. Stage 2 linked the data to disease outcomes, including cancer.

In the meta-analysis, individuals who were diagnosed with cancer before the study period were excluded, as were those who were diagnosed during the first year of follow-up. This was done avoid reverse causality, in which symptoms of an undiagnosed cancer cause stress at work.

For those included in the analysis, complete data were available for job strain, age, sex, socioeconomic status, body mass index, smoking status, alcohol intake, and incident cancer outcomes. At study baseline, participants were 17 to 70 years. Within the cohort, 5765 (5%) developed some type of cancer during the average follow-up of 12 years (522 developed colorectal cancer, 374 developed lung cancer, 1010 developed breast cancer, and 865 developed prostate cancer).

In all studies included in the meta-analysis, work-related psychosocial stress was defined as job strain. Questions from validated questionnaires, such as the Job Content Questionnaire and Demand–Control Questionnaire, were used to ascertain baseline job strain.

The researchers found that, after adjustment for age and sex, job strain was not associated with the overall risk for cancer (HR for any cancer, 0.95). There was also no association after multivariable adjustment (HR, 0.97). The associations were similar in analyses that included nonmelanoma skin cancer and those that excluded it.

The researchers also found no association between job strain and the risk for colorectal (HR, 1.16), lung (HR, 1.17), breast (HR, 0.97), or prostate (HR, 0.86) cancer. Thus, clear evidence demonstrating an association between job strain and the risk of cancer is lacking.

The IPD-Work Consortium is supported by the EU New OSHERA research program (funded by the Finnish Work Environment Fund, the Swedish Research Council for Working Life and Social Research, and the Danish National Research Centre for the Working Environment), the Academy of Finland, the BUPA Foundation (grant 22094477), and the Economic and Social Research Council in the United Kingdom. The authors have disclosed no relevant financial relationships.

BMJ. Published online February 7, 2013. Abstract