To see what role job stress might play in the risk of developing cancer, Heikkila's group collected data on 116,000 men and women, aged 17 to 70, from Finland, France, the Netherlands, Sweden, Denmark and the United Kingdom.
All of these people had taken part in one of 12 studies where they were asked about the amount of stress on their job.
The researchers defined several types of job stress: high-stress jobs, with high work demands and low control over work; active jobs, with high demands and high control; passive jobs, with low demands and low control; and low stress jobs, with low demands and high control.
The investigators then turned to cancer death registries and hospital records to see how many people developed or died from cancer. They further refined their search by taking age, sex, socioeconomic factors, smoking and alcohol use into account.
In addition, the researchers excluded anyone who was extremely overweight or underweight.
Over an average 12 years of follow-up, more than 5,700 people developed some type of cancer.
Heikkila's team didn't find any connection, however, between cancer and job stress. It is possible that other studies that found a connection between job stress and cancer found the association by chance or included other work-related factors that went beyond work, the Finnish researchers said.
For this type of study, called a meta-analysis, researchers comb through already published studies looking for patterns in the data. Often, the patterns they find go beyond the original intent of the studies they are examining.
The downside of a meta-analysis is that the data the researchers choose is only as good as the data in the studies they use, and their conclusions can't always take into account problems with the original research.
Elizabeth Ward, national vice president of intramural research at the American Cancer Society, said it
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