By Katherine M. Venables
Occupational epidemiology is one of those fascinating areas which spans important areas of human life: health, disease, work, law, public policy, the economy. Work is fundamental to any society and the importance society attaches to the health of its workers varies over time and between countries. Because of the lessons to be learned by looking at other countries as well as one’s own, occupational epidemiology is a truly global discipline. Emerging economies often prioritize productivity over other issues, but also can learn from the long history of improvement in working conditions which has taken place in developed countries. Looking the other way, the West can learn from fresh insights gained in studies set in low and middle-income countries.
Exposures are usually higher in emerging economies and epidemiological methods are an important tool in detecting and quantifying outbreaks of occupational disease which may have been controlled in the West. A recent study of digestive cancer in a Chinese asbestos mining and milling cohort provides additional evidence that stomach cancer may be associated with high levels of exposure to chrostile asbestos, for example. This was a collaborative study between researchers in China, Hong Kong, Japan, and the United States, and illustrates the way that studying an “old” disease in a new context can provide results which are of global benefit.
Issues in occupational epidemiology are never static. Work exposures change along with materials and processes. The ubiquitous printing industry, for example, is always developing new inks, cleaning agents, and processes. A cluster of cases of the rare liver cancer, cholangiocarcinoma, was noted in Japanese printers and this finding was replicated in the Nordic printing industry by using one of the large Nordic population-based databases. This replication is important because it shows that the association is unlikely to be due to a lifestyle factor specific to Japan.
“Big data” sharpens statistical power and there are now specific data pooling projects in occupational epidemiology, to supplement the use of existing large databases. The SYNERGY study, for example, pools lung cancer case-control studies with the aim of teasing out occupational effects from behind the masking effect of smoking, which remains by far the most important driver for lung cancer. A recent analysis with around 20,000 cases and controls was able to show that bakers are not at increased risk of lung cancer, whereas the many previous smaller studies had given inconsistent results.
The addition of systematic reviews to the toolkit has strengthened the evidence base in occupational epidemiology, allowing policy about occupational risks and their prevention to be made with confidence. Health economics, also, can be applied to findings from occupational epidemiology to clarify policy issues.
Development brings its own issues to which occupational epidemiology can be applied. We now live longer in the West, and we will have to work into old age, often while carrying chronic diseases. Despite frequently-expressed concerns about an ageing workforce, a recent study in an Australian smelter confirmed others in that the older workers maintained their ability to work safely and the highest injury rates were in young workers. Patients with previously fatal diseases survive into adult life and, potentially, the workforce; a survey of patients with cystic fibrosis, for example, found that disease severity was less important as a predictor of employment than social factors such as educational attainment and locality. A loss of heavy industry in the West, combined with cheap transport, means that many of us spend most of our waking hours sitting down, promoting obesity and its complications. A sample of UK office workers spent 65% of their work time sitting and did not compensate for this by being more active outside work. The economic downturn is a major political and social preoccupation, bringing uncertainty about future employment, which may fuel dysfunctional behaviour such as ‘presenteeism’. A Swedish study suggested that this may be associated with poor mental wellbeing.
Katherine M. Venables is a Reader in the Department of Public Health at the University of Oxford. Her research has always focused on aetiological epidemiology. At Oxford, she has worked on a cohort study of mortality and cancer incidence in military veterans exposed to low levels of chemical warfare agents, and also on the provision of occupational health services to university staff. She is editor of Current Topics in Occupational Epidemiology.
Image: Woman smoking a cigarette by Oxfordian Kissuth. CC-BY-SA-3.0 via Wikimedia Commons.