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20 December 2016

Cancer all-clear for night work was based on ‘bad science’

An Oxford University study that concluded the classification of night work as a cause of breast cancer in women is no longer justified was based on ‘bad science’, top researchers have warned.

The large scale ‘meta-analysis’, published online on 6 October 2016 in the Journal of the National Cancer Institute (JNCI), concluded “night shift work, including long-term night shift work, has little or no effect on breast cancer incidence.” It added the International Agency for Research on Cancer’s (IARC) ranking of night work as a ‘probable’ cause of breast cancer in women “is no longer justified.”

But three of the most respected epidemiologists on night work and breast cancer have now said they “fully disagree” with this conclusion, noting a succession of methodological flaws in the research “invalidate” its conclusions.

Harvard Medical School epidemiologist Eva Schernhammer told Hazards magazine that given the Oxford study’s “bad science”, it was “not surprising” it found no effect.

Johnni Hansen, a researcher with the Danish Cancer Society, was equally unimpressed. “They base their conclusion on a poor study, but even worse is that their conclusion may hinder preventive initiatives for night workers,” he said.

The main cohorts in the Oxford study, which was financed by the Medical Research Council, the Health and Safety Executive (HSE) and Cancer Research UK (CRUK), were “worryingly old”, with many over retirement age, and the follow up was “unusually short”, Hansen said.

The risk of women developing breast cancer appears to wane in the years after night working ends, so studying retired workers without recent exposures misses the point and the cancers, said Schernhammer. She said the higher risk is seen in women with long exposures – at least 15 years – early in their careers.Source: Hazards magazine

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