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eISSN: 2475-5494

Women's Health

Review Article Volume 8 Issue 1

Shift work and risk of cancer in women

Yahya Rasoulzadeha,1 Mahdi Hosseinpourib,2 Vahid Mirzaic,1 Omran Ahmadid1

1Department of Occupational Health Engineering, Tabriz University of medical sciences, Iran
2Department of Statistics, Persian Gulf University of Bushehr, Iran

Correspondence: Omran Ahmadi, Department of Occupational Engineering, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran, Tel 9144241240

Received: November 09, 2019 | Published: January 22, 2019

Citation: Rasoulzadeha Y, Hosseinpourib M, Mirzaic V, et al. Shift work and risk of cancer in women. MOJ Womens Health. 2019;8(1):60-61. DOI: 10.15406/mojwh.2019.08.00212

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Abstract

Despite the benefits of shift work for the general public, the workers themselves are primarily affected by their complications. Many epidemiological studies have mentioned the relationship between work shift and cancer. These studies have focused on the potential negative effects of work-shift jobs, in which the night-light hypothesis and melatonin have received special attentions. This review study details the recent studies and discusses the underlying mechanisms, assumptions and results from epidemiological and laboratory studies on the incidences of cancer in women shift workers. A total of 100 articles were searched, from which 40 were studied. Some recent studies have focused on the relationship between night work shift and breast cancer. The results of the study indicate non-significant correlation between work-shift and cancer in general, but particularly, there is a significant relationship between work-shift and breast cancer.

Keyword: shift work, risk, cancer, occupational health, women

Introduction

Over the last 50 years, the shift working has increased significantly in all developed and developing countries such as Iran.1,2 According to the latest statistics, about a quarter of the workforce in the United States is shift working.3,4 From a scientific point of view, the definition of shift work is: “employment at work outside of normal working hours, that is, outside the time period (7 am to 6 pm)”.5,6 Despite the usefulness of the shift work for the general public, the workers themselves are mainly affected by the complications.7 Lighting the midnight environment causes physiological changes in the secretion of the melatonin hormone.8 In a number of epidemiological studies focusing on the relationship between shift work and cancer, attention was focused on the potential negative effects of shift work, with the special emphasis on nighttime light and melatonin. In these studies, there has been an inverse relationship between continuous exposure to light at night and melatonin level.8,9 This reduction in melatonin production is detailed in a hypothesis that light exposure results in an increase in the production and amount of hormones such as estrogen, as well as changes in the growth trend of hormones Tumors in the chest.9,10 According to the results of objective studies, the risk of lung and breast cancers is high in individuals who worked as shift workers.11 The results of laboratory studies and animal studies have shown that the effects of low production of melatonin are not limited to breast cancer.12,13 This review study details the recent systematically studies, and discusses the underlying mechanisms, assumptions, and results from epidemiological and laboratory studies on the incidences of cancer in women shift workers.

Method

This is a review article on shift working and its relation to women cancer. The results of the study include the results of recent papers on shift working and its association with cancer as well as chronic diseases, which were worked out as a review of studies by July 2016. To search for the desired articles from the combination of cancer keywords, shift work, the chance of cancer in PubMed, Google Scholar and science direct A total of 100 articles were searched with the keywords mentioned, from which 40 articles related to this topic where chosen. The main results of the papers were summarized and are explained in greater detail. Articles include epidemiological studies of groups that work continuously as shift workers, people who work on a daily basis or often work at night rotational and people work for daily. In this overview, the term "shifts work" was used to compare any type of job that was characterized as an abnormal and irregular working hours with people who regularly work for daily.

Results

Recent studies have focused on the relationship between night work shift and breast cancer. Details of studies on shift work and the risk of developing cancers are presented. In the study of IARC groups, out of eight studies, six with long-term night shifts were shown to have an increase in the risk of cancer compared to those who did not work at night.14 In the study of night work and the risk of breast cancer among Norwegian nurses, there was a strong correlation between increased risk of cancer in nurses working for more than 5 years with 6 night shift per month (OR=1.8). There was no significant relationship between the duration of work and the risk of incidence of cancer.15 Also, in the cohort study by Pronk. on Chinese women, there was no significant increase in the duration of work shift and the risk of cancer.16 Knutsson and colleagues studied breast cancer among shift workers in a cohort study. For people working during day time OR was 1.3 while for those with a night shift it was 2.02, suggesting an increase in the risk of developing cancer among women shifting overnight.17 In a study by Megdal.17 who conducted a systematic study and meta-analysis of 13 types of studies in 2005, in seven studies the relationship between breast cancer and the night shift was indicated with RR=1.48. The results of this study showed that there is a relationship between long-term overnight shift and increased risk of developing breast cancer.18 Peplonska in his study on nurses showed that working 8 times or more in the form of night shifts per month can interfere with the synthesis of melatonin.19 Anne Grundy showed that there is a relationship between long-term night shift with increased risk of breast cancer.15

Kolstad conducted a systematic review of the relationship between shift work nighttime and breast cancer and other cancers indicated that there is no evidence related to night shift work and the risk of developing cancer in different parts of the body.20 Hansen in a case-control study, showed an increase in the risk of cancer among women who work mainly at night (RR 1.5 in men and 1.7 in women).21 Davis et al worked on the risk of breast cancer and shift work and showed an increase in the risk of cancer among women (RR 1.06 in men and 1.6 in women).22 The cohort study of Schernhammer on shift work and risk of breast cancer in women showed an increase in the risk of cancer among women (RR 1.08 in men and1.36 in women).23

Conclusion

Shift workers are faced with a variety of risk factors that affect the risk of cancer. Increased exposure to light at night is believed to be one of the probable causes of breast cancer in the industrialized world. The nighttime brightness may affect the natural secretion of melatonin and more likely to be secreted. Suppressing the production of melatonin may be a risk factor for breast cancer by direct and indirect mechanisms, such as dangerous changes in the concentration of sex hormones. This epidemiological review details a relationship between shift work and the risk of cancer. There are definite evidences for the relationship between shift work and the risk of breast cancer, but there is limited evidence of the relationship between night work and cancer in other parts of the body. A number of mechanisms may form such relationship, including affecting the production of melatonin, sleep disturbances and lifestyle. In most studies, disturbances in circadian cycles under the influence of night lighting are one of the higher risk factors for cancer than other factors, such as the physical indices of night workers or the smoking habits of night workers. The results of epidemiological researches should be used to develop the information of work regulations and public health interventions and reduce the risk among shift workers. In addition, the duration and frequency of exposure, working history and demographic characteristics and other factors may influence the incidence of cancer.

Acknowledgements

None.

Conflict of interest

The author declares there are no conflicts of interest.

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©2019 Rasoulzadeha, et al. This is an open access article distributed under the terms of the, which permits unrestricted use, distribution, and build upon your work non-commercially.

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