Night-shift work as a risk factor for breast cancer in women

¶ … Working Night Shift and Getting Cancer

The increasing rate of women acquiring breast cancer disease has been an alarming issue in the medical history of cancer prevention and studies. The many research and studies conducted by medical professionals on breast cancer disease have found a number of cancer-causing habits and lifestyles. Among those that have been examined and found as risk factors of breast cancer on women is night-shift work.

Regularly working in night shift as a health-hazardous cause of breast cancer has been investigated by several studies of different cancer research institutions. Almost all studies were carried out based from employment histories of women diagnosed of breast cancer. In a population-based study conducted by Fred Hutchinson Cancer Research Center, it was found that women who regularly work at night are at 60% risk of developing breast cancer. The most significant risk factor to this is the exposure to bright lights at night.

From USA Today's article Working Night Shift may Raise Breast Cancer Risk, two studies published in the Journal of National Cancer Institute (JNCI) indicated a link between breast cancer and night shift work. The article states that The studies, both appearing in the Journal of the National Cancer Institute, suggested a "dose effect," meaning that the more time spent working at nights, the greater the risk of breast cancer." (USA Today, 2001).

This paper discusses the causes and effects of working night shifts as related to breast cancer.

It will include general explanations why working at night increases the rate of developing breast cancer on women. A number of conducted studies and literatures will be used as references for this research paper.

Epidemiological Studies on Working Night Shift and Cancer

Currently, there are only a few studies that examine the direct relationship of working night shift and breast cancer. Based from the several studies that used different methods, medical researches have hypothesized that working night shifts puts women at greater risk of breast cancer. In a research led by Scott Davis, in an aim to evaluate and investigate the relation of night-shift work and breast cancer, a strong result shows that women who regularly worked on night shifts have greater risk of developing breast cancer than those who worked on day shifts (Recer, 2001). The investigation was conducted on 763 breast cancer diagnosed women and 741 women with no breast cancer. Based on the work history of the participants, and compared to those with no breast cancer, the study found that women who worked on night shifts for three years or less are at 40% more risk of having breast cancer, while those who worked for more than three years are at 60% risk (Recer, 2001).

Another study, conducted by Francine Laden from Harvard Medical School, has shown a link of night shift work to breast cancer. Using investigation data on 78,562 nurses who worked on rotating night shifts, the study found that those who worked at night for at least three times a week, and for less than 30 years are at 8% more risk of developing breast cancer (Recer, 2001). On the other hand, those who worked for 30 years or more are at 36% risk (Recer, 2001).

The studies of Scott and Laden, though are relatively small in statistics, show results of a significant link between working night shifts and breast cancer. To provide a stronger basis of the hypothesis that working night shifts is a risk factor to breast cancer, Scott and Laden suggest that further investigation be made to allow a compelling case against the unhealthy effects of night shift schedules.

A similar study, according to the American Cancer Society, indicates that working in night shifts increases women's lifetime risk of getting breast cancer from 12.5% to above 16%. This leads to an increasing rate of women's deaths from breast cancer. In the United States, there are 175,000 annual increases of breast cancer patients while 43,700 women die of breast cancer (Recer, 2001).

Researches show that women who work at night until morning are exposed to bright light that can decrease their body's supply of melatonin. This lack of melatonin is said to be the main cause of breast cancer for night shift workers. Melatonin is a brain hormone that is naturally produced at night in darkness. It helps in the prevention of tumor development and growth. Also, it acts as a regulator in the body's production of estrogen. A body that lacks melatonin may overproduce estrogen that can affect the growth of breast tissues. Thus, a decrease in melatonin risks a woman's body to develop breast cancer tumors.

Another study conducted by Johnni Hansen of Copenhagen's Institute of Cancer Epidemiology indicates similar result showing that working in night shift is a risk factor to breast cancer. The study was carried out on 7,000 Danish women who are breast cancer patients. Based from the examination of the participants, the study revealed the following results.

The findings show a 50 per cent higher risk of primary breast cancer among women aged thirty to fifty-four years who worked night shifts for at least half a year, than for women in the same age group who worked days. Among women who had worked night shifts for six years or more, the risk jumped to 70 per cent." - (CUPW, 2001).

Hansen's study considered other risk factors of breast cancer as adjustments to the study's results. This includes alcohol consumption, stress, and socio-economic status. Despite of this, the study indicated the lack of melatonin as the common factor that exists to breast cancer participants.

Other Links to Working Night Shift and Breast Cancer

Aside from a decrease in melatonin level, exposure to bright light, and increase level of estrogen, another risk factor of breast cancer that is being looked at on night shift workers is stress. According to studies, there are several factors that could affect the mechanisms of the body when working at night. One of which is stress.

Sid Kirchheimer, in his How Sleep Affects Cancer, indicates the following relation of stress hormone in cancer.

Cortisol is the so-called 'stress' hormone triggered, along with others, during times of anxiety and may play a role in the development and worsening of cancer and other conditions."

In a study conducted by David Spiegel, a psychiatrist at Stanford University, together with Sandra Sephton, it was revealed that those who work in night shifts experience "shifted cortisol rhythm" which affects body mechanisms that in turn affects breast cancer risks factors such as estrogen level.

Another finding in Spiegel and Sephton's study indicates that cancer patients who are able to manage their stress effectively improve better than those who cannot handle their stress (Kirchheimer, 2003). In addition, stress becomes a detrimental factor to the sleeping habit of cancer patients that in turn may affect their hormonal production of melatonin. Kirchheimer further indicates that Just last week, Swedish researchers said women under a lot of stress may double their risk of breast cancer compared with those who remain calm when life throws them a curveball."

Spiegel concluded his report by stating that cancer is also influenced by stress and sleep, and that such factors should be taken seriously as preventive measures against cancer.

Conclusion

The studies and epidemiological literature that were presented in this paper on the relationship of working night shift and breast cancer have all shown significant results of the detrimental effects of night shift work to an individual's health as related to breast cancer.

Two known studies relevant to this paper's subject, one conducted by Scott Davis, and the other conducted by Francine Laden and her colleagues, revealed that women who work in night shifts have an increased risk of breast cancer. This was explained by the decrease in level of melatonin due to lack of night sleep, exposure to artificial lights at night, and increase level of estrogen. Other study, particularly on the influence of stress that workers develop during night shift duties, shows unfavorable relationship of stress to body mechanisms that can be detrimental to cancer.

Currently, there are only few available studies that focus direct examination on the correlation of night shift work to breast cancer and other types of cancer. As Scott and Laden suggest, the number of accounts in their studies are relatively small, and that further research and investigation is needed to provide a stronger support and more proof to their findings.

The findings that reveal a significant relationship of night shift work to cancer is still a contention in the medical field. To provide a compelling case against night shift work, it is suggested by many concerned organizations that further study be made on the subject.

Policies to Address the Issue

To better address the issue of night shift schedules as a risk factor of breast cancer, future epidemiological studies must focus on methods that can present more clarity and certainty of the findings. This may include investigations focusing on the different effects of night shift work as related to workers' health and as related to cancer risk factors. Rather than focusing on the same findings and variants used by previous studies, such as the relationship of melatonin and bright artificial lights to breast cancer, future studies can provide more information by using and investigating on other factors of night shift work that can become risks for breast cancer.

Anthony Swerdlow, in his Shift Work and Breast Cancer: A Critical Review of the Epidemiological Evidence, recommended investigation techniques that can be used to further the studies of night shift work and cancer.

The first is the use of occupational circumstances as variants of the investigation. Considering this factor will be helpful in comparing the differences between night shift and day shift workers as it oftentimes has similar existence in night and day schedules. The second is the use of large cohort designs from which detailed data will be gathered from large participants.

HSE (Health and Safety Executive) addressed the issue of night shift work as risk of breast cancer by calling medical experts, locally and internationally, to share ideas on how further conclusive research and studies on the subject will be conducted. They stated that Without conclusive research, we cannot develop definitive guidance on the risks from nightshift work."

For women who work in night shifts, a step to address the issue of night shift work and breast cancer is to obtain enough information about breast cancer disease. Because it would be impossible for some sectors in our society today to eliminate a round the clock work, taking precautions for one's self would help in the prevention of breast cancer. Taking a regular visit to breast cancer specialists and getting regular mammograms are the best advice for those who work in night shifts. Or, as much as possible, work must be done in daytime, and, use much of the nighttime in acquiring sufficient sleep. Dr. Joseph Mercola, in his Sleep in Total Darkness to Decrease Cancer Risk, recommends sleeping in absolute darkness to lower risk of cancer. He even recommends installation of "black out" drapes for those whose rooms are slightly lit by lights from outside.