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.
Links to Working Night Shift and Breast Cancer
The most addressed causes that links night shift work to breast cancer among the breast cancer participants of the studies mentioned in the previous section is the decrease in level of melatonin and the exposure to bright artificial lights at night.
As a reference and background to our discussion of melatonin and bright lights as risk factors to breast cancer, the following are some information on melatonin from the article Light at Night and Risk of Breast Cancer.
A melatonin, the "hormone of the darkness," is produced by the pineal gland during the hours of darkness, melatonin has been found to restrain the growth of tumors in experiments with animals, melatonin serum levels in humans decrease when people are exposed to light at night, decreased melatonin levels may enhance the development of tumors, studies have shown that blind women have a 20-50% lower risk of breast cancer than do women with normal vision, the evidence of a relation between melatonin and risk of cancer in humans is conflicting, but the majority of reports indicate a protective action of melatonin.
Studies concerning working night shifts as a risk factor to breast cancer have revealed that melatonin greatly affects the rate of getting breast cancer among women who work at night until early morning. An explanation to this is that a lack of melatonin, a hormone whose production is restrained when sleeping at night is deprived, puts the body into risk of developing tumors such as breast cancer.
Melatonin is a hormone that is essential for the body. It acts as a protection against the growth and development of tumors. According to studies, during sleep at night is the peak time when melatonin is produced, specifically between 1 am to 2 am. Because working night shift deprives an individual from a night sleep, production of the right amount of melatonin is also being deprived. Thus, allowing a higher risk of developing cancer tissues. Daniel DeNoon, in his Hormone Melatonin Slows Breast Cancer, indicates the following report of David E. Blask of Bassett Research Institute in Cooperstown, N.Y. about the relationship of melatonin to growth of breast cancer.
The nighttime hormone melatonin puts breast cancer cells to sleep. It also slows breast cancer growth by 70%.
Another finding that causes a decrease in the production of melatonin is exposure to bright light.
Women who work night shifts are usually exposed to bright artificial lights. Studies show that bright light restrains the production of melatonin. Jeanie Lerche Davis, in her Breast Cancer and the Night Shift: Is There a Link?, indicates the following findings of Scott Davis, a breast cancer specialist.
Bright light at night seems to interrupt that cycle (production of melatonin), significantly reducing the amount of melatonin that is produced, says Scott Davis, PhD, researcher at the Fred Hutchinson Cancer Research Center, and chair of epidemiology in the School of Public Health and Community Medicine at the University of Washington in Seattle."
In his study, Scott Davis used light at workplace and light in home bedroom as two variants of sources of light. His study's findings show that women who worked night shifts and were exposed to light at their workplace had 60% increased risk of breast cancer (Davis, 2001). Similarly, those who were exposed to bright bedroom lights at night while trying to sleep are also at risk to getting breast cancer (Davis,…