Long term night shift work, a risk factor for breast cancer: Study

Working night shifts for over 30 years could double chances of breast cancer in women, according to scientists. The effect of night shift work was the subject of a study by Canadian researchers, the results of which were published in the British Medical Journal. The researchers looked at whether night shifts were tied with increased risk of breast cancer.

They study was carried out on 1,134 women with breast cancer and 1,179 women without the disease, but of the same age, in Vancouver, British Columbia, and Kingston, Ontario.

There have been suggestions about shift work as a risk factor for breast cancer, but doubts have persisted about the strength of the findings, largely because of issues around the assessment of exposure and the failure to capture the diversity of shift work patterns.

Previous studies have largely been confined to nurses rather than the general population.

The women, from varied employment background, were asked about their shift work patterns over their entire work history, while hospital records were used to determine tumour type.

Professor Kristan Aronson of Queen's University in Kingston, Ontario, sought to extend the findings to include prolonged shift work in non-health professions as well.

According to authors, this might be important as risk factors varied according to hormone sensitivity, and the sleep hormone melatonin, disruption to which had been implicated in higher breast cancer risk among night shift workers, might boost oestrogen production.

"Long-term night-shift work in a diverse mix of occupations is associated with increased breast cancer risk," Aronson and her co-authors concluded in the journal Occupational and Environmental Medicine.

The researchers also considered lifetime occupational histories to factor in both rotating and permanent night-shift schedules in the women, most of whom were in their mid to late 50s.

Hospital records were also reviewed for information on cancer diagnoses.

About a third of women in both groups reported having a history of night shift work.

According to Aronson who spoke in an interview yesterday, the ultimate aim of the study was to prevent breast cancer all together. She added if it was an environmental risk factor for breast cancer, healthy workplace policy could be developed that would reduce the impact of shift work on women.