Women working in night shifts are twice as likely to develop breast cancer as those working in day shifts. The risk of developing breast cancer becomes four-folds if they prefer to fall into the category of 'morning people'. Danish researchers have found the connection between night shift work and breast cancer after assessing the medical records of 18,500 women that served the Danish Army between 1964 and 1999. The link was observed in women who had worked for the least of three night shifts a week for the minimum of six years.
Women who described themselves as being one of the morning people were exposed to four times the risk of breast cancer. On the other hand, women who preferred to stay up late at night were only twice as likely to have breast cancer as those not working during nights, but were less affected than those who complained about night shifts.
Disruption to the body clock and alteration in melatonin hormone levels (darkness hormone) was identified as the reason for the disease. Night shifts expose a person to light at night, which reduces the production of melatonin. This weakens the shield against certain cancers.
Morning people who have had difficulties in coping with nigh shifts were observed to be stressed and sleep-deprived. Moreover, repeated changes in work schedule also led to deregulation of the circadian cell cycle of the examined women.
Several researches and studies have linked disruption of internal biological clock due to work schedule (jetlag) by way of impact on health in the form of lack of sleep, cardiovascular and metabolic effects. This study has further highlighted the adverse effects of shift work by relating night shifts with cancer.
Research questionnaire retrieved aspects of everyday life such as lifestyle pattern, family issues and sun exposure from the subjects. They were also asked to provide details of any serious illness, treatment method, especially hormone replacement therapy and contraceptives that they may have undergone.
The research results were published in the journal Occupational and Environmental Health, which revealed the work of the research panel at Institute of Cancer Epidemiology (Copenhagen). The panel was headed by Dr Johnni Hansen.