Lightning and Human Circadian Clock Term Paper

Pages: 4 (1174 words)  ·  Bibliography Sources: ≈ 2  ·  File: .docx  ·  Topic: Disease

¶ … Industrial Revolution, most people worked and carried on their daily life activities exclusively in the daytime and slept at night, primarily because without artificial lighting, there was no other choice. Once kerosene, gas, and incandescent lighting became widely used during the nineteenth century, people were able to make more productive use of nighttime hours, and 24-hour production became a possibility.

Artificial lighting has become so common, that in modern societies, we take nighttime sporting events, all-night restaurants, and 24-hour casinos for granted. Certain industries run 'round the clock, with rotating shift workers on duty at all times.

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When medical researchers realized that certain illness rates, such as colorectal cancer and breast cancer, are much higher among nighttime shift workers than in the rest of the population, they began searching into the reasons for the link between nighttime shift work and those higher illness rates. One of the most significant discoveries is that exposure to light during the nighttime hours triggers a response in specific nerve cells within the eye that, in turn, initiates a mechanism that makes us more susceptible to disease. This is a result of disruption in the normal circadian rhythm of sleep-wake cycles, because normal production levels of the hormone melatonin within the pineal gland is regulated by the circadian rhythm. Melatonin is known to have certain anti- cancer roles. Therefore, inhibition of melatonin production naturally increases cancer rates of those types. The implications are that sleep deprivation is not just a matter of how many hours we sleep, but also a matter of sleeping in complete darkness and avoiding schedules that interrupt the circadian rhythm.

The Link between Nighttime Lighting and Cancer:

Term Paper on Lightning and Human Circadian Clock Assignment

When differences in cancer rates between daytime workers and nighttime shift workers first became apparent, researchers designed experiments to investigate any possible causal relationships between those observations and the identifiable differences between daytime and nighttime working factors. Among the elements of nighttime work considered was the factor of regular nighttime exposure to artificial lighting.

Since the two diseases noticed to increase most among nighttime workers were colorectal and breast cancers, researchers devised tests using cancer cell implantation in laboratory mice. Those experiments involved implanting human colorectal and breast cancer cells in mice and then separating the mice into different test groups. Some test groups of mice were kept in normal lighting situations where they were alternately exposed to light and then allowed to sleep in total darkness; the other groups were exposed to various types and levels of light throughout the night in addition to regular daytime lighting. The results of these experiments and others suggest that, like humans, mice exposed to light at night developed much higher rates of cancers, because the tumors grew much faster in the groups of mice exposed to nighttime lighting.

Circadian Rhythm, Melatonin Production, and Cancer:

Melatonin is a hormone that plays a role in inducing sleep, and it is known to be produced by the pineal gland in the center of the brain, with its highest rates of actual melatonin production triggered during the early morning hours. Both types of human cancer observed to increase in nighttime shift workers are related to melatonin, because both colorectal cancers and healthy breast tissue have specific hormonal receptor sites for melatonin. Earlier research discovered that the eye contains special cells within the retina that are responsible for regulating the circadian sleep-wake cycle. The circadian sleep- wake cycle is what regulates melatonin production levels, and the cancers that increase in nighttime shift workers (and laboratory mice… [END OF PREVIEW] . . . READ MORE

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How to Cite "Lightning and Human Circadian Clock" Term Paper in a Bibliography:

APA Style

Lightning and Human Circadian Clock.  (2007, October 11).  Retrieved October 25, 2020, from

MLA Format

"Lightning and Human Circadian Clock."  11 October 2007.  Web.  25 October 2020. <>.

Chicago Style

"Lightning and Human Circadian Clock."  October 11, 2007.  Accessed October 25, 2020.