Toil and trouble

Work is both good and bad for you. There is lots of evidence to show that being in employment is associated with a longer and healthier life; there are also countless reports of people suffering harm in the workplace.

Victorian chimney sweeps developed scrotal tumours caused by carcinogenic soot, while wool-sorters were killed by anthrax. Even in our modern, regulated working environment, there are still serious hazards. Recent research, presented at the annual meeting of the Society of Occupational Medicine, shows that 5.3 per cent of cancers are caused by occupational factors. These include exposure to mineral oils, asbestos, radon, coal tars, UV sunlight and, interestingly, shift work.

Shift work is interesting because it does not have the usual mechanism for producing cancer. Coal tar and radiation, for example, cause cellular damage which can be observed at microscopic level. So how could shift work result in a tumour? Some theories point to a disruption of circadian rhythms. These originate in an area of the brain named the suprachiasmatic nucleus (SCN), very close to the optic nerves. When daylight fades, it produces more melatonin, which causes sleepiness. There are other, normal peaks and troughs in hormone activity during the day; however, in stressed, sleep-deprived or physically exhausted subjects, the circadian rhythms seem to weaken. “Clock genes”, which mediate circadian rhythms, are required to ensure that cells are working correctly, and in animal studies, there are concerns that faulty clock genes can cause cancer.

More investigation is needed in humans, particularly as there has been a small increase in breast cancer risk in shift workers such as nurses and flight attendants. A review from the Health and Safety Executive found that there was an “appreciable” link between breast cancer and shift work, but “it remains unclear whether any association is causal”.

Linking cause and effect is notoriously difficult in such contexts. A randomised controlled trial tries to ensure that the only difference between two compared groups is a single factor – exposure to diesel, say – so that any difference in cancer rates has a clear cause. But occupational health studies cannot use a pure randomised model, so research may not be conclusive.

Meanwhile, there are still cancers being caused by preventable work-based factors such as mesothelioma (cancer of the lining of the lung caused by asbestos). These often affect people who already have a higher risk of earlier death – manual workers and people at lower employment grades. If we are serious about reducing health inequalities, this would seem a good place to start.

Margaret McCartney is a GP in Glasgow.

margaret.mccartney@ft.com

Follow Margaret McCartney’s blog