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Circadian rhythm and cancer

What we know about circadian rhythm? Circadian rhythms refer to the endogenous rhythms that are generated to synchronize physiology and behavior with 24-h environmental cues.

According to scientists, certain human genes are responsible for the circadian rhythm and if mentioned genes wouldn’t work properly (in the usual natural way), chances for cancer development could increase. Damaged and/or transformed genes due to circadian disruption may be involved in the transformation of normal cells into cancer cells. Several studies have indicated an epigenetic basis for the carcinogenic effects of circadian disruption.

Scientists already explained the carcinogenic effects of circadian disruption and highlighted its potential role in different human cancers using an epigenetic viewpoint.

Human body physiology is set to a regular switch from day to night and from night to day. Accordingly, hormonal fluctuations occur at certain time of the day – actually specific genes switched on and off at certain times of the day (regulating hormone production). For example, growth hormone increases at night and glucocorticoids reach its peak before awakening.

All mentioned processes are controlled by biological clock system (so called “circadian rhythm”) which sends signals to genes, cells, tissues and organs – letting human body to recognize the time of the day. Biological clock system is vital and any disturbances could affect the state of our health.

Circadian rhythm can be broken easily. Late sleep, sleep mistakes (nights in front of a computer screen, mobiles in the bed, late dinner), short sleep or regular travel through several time zones could trigger disturbances in the circadian rhythm. If you don’t sleep during night (as it is requested by normal healthy biological clock system), circadian rhythm acts as during day time and body continue producing day hormones. As a result, daily schedule of molecular gene activity could be disturbed – it can cause a variety of unpleasant health consequences. Disruption of circadian rhythms (so called “circadian disruption”) affects many biological processes within the body and results in different long-term diseases, including cancer.

Circadian rhythm and cancer

Circadian rhythm disturbances affect whole nervous system and change the speed and quality of metabolism. According to health experts, regular late sleep and short sleep could cause diabetes or obesity.

Circadian rhythm is responsible for variety of metabolic and physiological functions. Accumulating epidemiological and genetic evidence indicates that the disruption of circadian rhythms might be directly linked to cancer. Researchers from Massachusetts Institute of Technology were able to demonstrate in their experiments the causal relationship between circadian rhythm disorders and the likelihood of the cancer in the body. Abnormal metabolism in cancer could also be a consequence of a disrupted circadian clock.

The circadian clock imparts 24-hour rhythmicity on gene expression and cellular physiology in virtually all cells. Disruption of the genes necessary for the circadian clock to function has diverse effects, including aging-related phenotypes. Some circadian clock genes have been described as tumor suppressors, while other genes have less clear functions in aging and cancer.
Elizabeth A. Yu; David R. Weaver; University of Massachusetts Medical School, Worcester, USA

The circadian clock is the body’s molecular clock, a natural, roughly 24-hour cycle that regulates sleep, metabolism, the immune system, temperature, renal function, gene activity and other physiological and biochemical processes. Circadian rhythms occur in all the body’s organs, tissues and cells and are synchronized by a central pacemaker in the brain’s hypothalamus.

There is considerable evidence that shift work, jet lag, light at night or other disruptions to the circadian clock can lead to cardiovascular disease, obesity, diabetes, hypertension, depression and other health problems. In 2007, the International Agency for Research on Cancer classified shift work resulting in circadian disruption as a probable human carcinogen.

Desynchronized circadian rhythm seems to be implicated in several pathologic conditions, including tumor development and progression of cancer. In 2007, the International Agency for Research on Cancer (IARC) categorized shift work that involves desynchronized circadian rhythm, as being probably carcinogenic to humans.
Christos Savvidis and Michael Koutsilieris, National and Kapodistrian University of Athens, Greece

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