Huge study finds no link between night shift work and cancer
Working night shifts on a regular basis does not increase the risk of developing cancer, researchers have said.
Melatonin, which some studies have suggested may have anti-cancer properties, is mainly produced by the body during sleep, but production is suppressed if people are exposed to light while they sleep.
It has therefore been suggested that night-time shift workers produce less melatonin and may be more at risk of breast, prostate and bowel cancers.
However, a new analysis of nearly 20 years' worth of data involving 3.2 million Swedish citizens has concluded that such concerns are probably unfounded.
Researchers from the Institute for Environmental Medicine in Stockholm divided the occupations of workers, who were all working for at least 20 hours a week in 1970, into groups depending on the percentage of shift work involved.
Lead author Dr Judith Schwartzbaum, associate professor of epidemiology at Ohio State University, explained: "We identified occupations where many employees worked during hours that could affect the production of melatonin."
Publishing their findings in the Scandinavian Journal of Work, Environment and Health, the researchers reveal they found no relationship between shift work and an increased risk of prostate, bowel or breast cancer, regardless of how much night-time work a person's job involved.
However, Dr Schwartzbaum pointed out that the effects of melatonin on human cancer development "are not well understood" and said a large-scale international study would be needed to confirm the results, especially as other recent studies achieved conflicting results.