In a study published in the British Medical Journal, Canadian researchers have warned that working night shift for more than 30 years can double a woman’s risk of developing breast cancer.
For the research, 1,134women with breast cancer and 1.179 women without the disease were studied. All the women were of same age.
The study was conducted in Vancouver, British Columbia, and Kingston, Ontario. It aimed at assessing whether working night shifts were linked to increased risk of breast cancer.
There was no evidence of any increased risk of developing breast cancer in women who had worked night shifts for up to 14 years or between 15 and 29 years.
But those who had worked nights for 30 or more years were twice more likely to develop the disease than others taking influential factors in account. Although the numbers recorded were small.
Various previous studies have hinted same results confined to nurses rather than the general population. Entire work histories were taken into account for women who had taken up several different jobs. Hospital records were checked to determine tumour types in such cases.
The strengths of the finding are being doubted for issues around the assessment of exposure and failure to capture the diversity of work shift patterns.
This may be important, said the authors, because risk factors vary according to hormone sensitivity, and the sleep hormone melatonin, disruption to which has been implicated in higher breast cancer risk among night shift workers, may boost oestrogen production.
The suggested link between breast cancer and shift work has been put down to melatonin, but sleep disturbances, upset body rhythms, vitamin D or lifestyle differences may also play their part, said the authors.
Risk was also higher among those whose tumours were sensitive to oestrogen and progesterone.
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