"Plain Language About Shiftwork," a report on the National Institute for Occupational Safety and Health website, defines night shift workers as those who work between the hours of 10 p.m. and 8 a.m. The article notes data from a 2001 survey by the Bureau of Labor and Statistics that estimates there are nearly 15 million shift workers in the United States. The report further comments that there are some health and safety risks associated with working the night shift.
Hormonal Cancers
Melatonin is a hormone produced by the pineal gland. Along with circadian rhythms, melatonin coordinates human sleep cycles -- it is lowest during the day when people are exposed to natural light, and highest in the darkness of the night. However, since the invention of the light bulb, humans have gained the possibility of unlimited exposure to light. According to the article, "Melatonin and Cancer Risk" published by the British Journal of Cancer in 2004, humans have not fully adapted to such exposure and consequently, shift workers, who are exposed to bright light at night, produce insufficient amounts of melatonin.
According to the 2004 article, melatonin appears to have tumor-suppressing activity. Melatonin suppression increases the production of reproductive hormones, namely estrogens. Estrogens stimulate breast tissue as well as the inner lining of the uterus, or endometrium. In excessive concentrations, estrogens are identifiable risk factors for breast and endometrial cancers.
Colon and Rectal Cancers
A brief communication in the 2003 issue of the "Journal of the National Cancer Institute," entitled "Night-Shift Work and Risk of Colorectal Cancer in the Nurses' Health Study," discussed the correlation between melatonin and colorectal cancers. Colorectal cancer patients tended to have lower blood levels of melatonin. The research findings correlated 15 years of rotating shifts, including night shift work, to higher risks for colorectal cancer. The relationship between night shifts and intestinal cancers was stronger the longer night shifts were worked.
Cardiovascular Disease
According to Anders Knutsson in the 2003 article "Health Disorders and Shift Workers," concentrations of cholesterol, total lipids, and glucose were raised during night shift work. Conclusively, researchers indicated that night work could have long-term cardiovascular effects. Knutsson's review of 17 other studies on night shift work and cardiovascular disease noted a strong correlation between night-shift work and ischemic heart disease and heart attacks in both sexes.
Digestive Concerns
In addition to the pattern that the circadian rhythms establish for melatonin production, the authors of "Melatonin and Cancer Risk" associate this rhythm to the functions of digestion. The article "Plain Language About Shiftwork" concurs, asserting that night shifts can interfere with normal eating and excretion patterns, leading to symptoms of constipation and diarrhea. Lack of nutrition was also stated as a possibility for ulcer formation and other digestive concerns, as vending machines may be the only sources of food available in the wee hours of the morning.
Compromised Pregnancy Outcomes
Although the causes have not yet been elucidated, Knutsson in his 2003 article also discusses strong evidence that suggests that pregnant female shift workers, including those who work nights, are at a higher risk for miscarriage, having a baby with low birth weight and preterm birth.
References
- National Institute for Occupational Safety and Health: "Plain Language About Shiftwork"
- National Sleep Foundation: "Shift Work and Sleep"
- British Journal of Cancer: "Melatonin and Cancer risk: does light at night compromise physiologic cancer protection by lowering serum melatonin levels?
- Journal of National Cancer Institute: "Night-Shift Work and Risk of Colorectal Cancer in the Nurses' Health Study"
- Occupational Medicine: "Health Disorders of Shift Workers"
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