Full-time employees face higher risk of cancer

Some of the risk factors for cancer are well known – smoking, alcohol, a sedentary lifestyle – while others are a bit harder to explain. For example, work. As part of the completed, SNSF-funded NCCR “LIVES” (see info box below), researchers at the University of Fribourg have demonstrated the existence of a link between the incidence of cancer and certain career paths. Published in Scientific Reports, their study (*) shows that women working full-time have a significantly higher risk than women who stay at home and that self-employed men are less likely to develop the disease than those who are salaried employees.

To obtain these results, the scientists analysed the work histories of 6809 women and 5716 men born between 1915 and 1945 in 14 European countries. They established associations between the risk of contracting cancer in the long term and eight career types, including ‘mainly full-time’, ‘mainly home/family’, ‘full-time or home/family to part-time’ or ‘mainly unemployment’.

New risks to be identified beyond smoking and alcohol

These results seem to contradict the old proverb that work is good for you. But only at first sight, insists the paper’s senior author Rose van der Linden, an epidemiologist and postdoctoral fellow at the University of Fribourg. According to her, no direct causal relationship can be established between the incidence of cancer and a person's career path.

“Correlation does not imply causation, and the aim of our research is primarily predictive,” she explains. “Our results show that we need to investigate further. My hypothesis is that the increased risk of cancer is linked to behaviours more commonly observed in full-time employees.”

These behaviours still need to be identified. The researchers adjusted the results to account for known cancer risk factors such as alcohol, smoking, body mass index, nutrition and physical inactivity. They are therefore probably not involved.

“At this stage, we can only speculate,” she adds. “Work-related stress, of course, could be a risk factor, as could some types of physical activity. At the moment, we are conducting a project on the possible effect of night shifts, because certain hormonal factors caused by sleep problems are linked to increased incidences of breast cancer, for example."

Worse conditions for women

Full-time employees are at greater risk than other categories – and this difference is even greater for women. Here too, scientists have to make do with hypotheses to explain this disparity. According to Rose van der Linden, “it is possible that women are exposed to more stress than men, to work that is less rewarding and more likely to cause depression, or to a damaging combination of professional activities and household chores. This is all the more true given that the cohort is comprised of subjects born in the first half of the 20th century, who spent their working lives in an era when gender discrimination was more marked than it is today,” she explains.

Other results also raise questions. For instance, what might explain the lower risk of cancer among self-employed men compared with salaried employees? “We can hypothesise that the self-employed are more motivated to take care of their health because they run a greater risk of losing their job if something goes wrong.”

The researcher stresses that this work is exploratory. As such, its main aim is to provide scientists with new avenues for identifying causes and informing occupational health policies. “For example, if we are able to determine a causal relationship between night shifts and cancer, we can assess the effectiveness of certain measures, such as limiting the length of night shifts or the number of years spent working night shifts, and issue recommendations accordingly.” Over such long periods, even modest changes in behaviour can have an impact on the risk of cancer. “We spend a lot of time at work, and I think it's important to understand the long-term effects. To do this, we need further studies,” concludes Rose van der Linden.

(**) S. Cullati et al.: Lifetime employment trajectories and cancer. Scientific Reports (2024)