Shift work may predispose to cancers

Posted by admin in Health

Writing in the South African Journal of Science Drs Beckett and Roden from the University of Cape Town, believe that disruption to circadian rhythms may play a role in the develoment of cancers.

Humans evolved in a changing environment, but an environment that essentially changed in a rhythmical way, according to these scientists. Organisms are able to adapt to changing patterns of daylength, temperature and rainfall, as well as to longer term regular changes such as climate. This internal ‘clock’ is what is refered to as circadian rhythms. 

The molecular basis of these circadian rhythms are ‘clock’ genes. Circadian clocks are found in most of the cells and tissues of mammals. It is the hormone melatonin that is crucial to the timing of the circadian system. Levels of melatonin peak at night. In mammals, including people, the pacemaker is found in a region of the brain called the suprachiasmatic nuclei (SCN). In addition, melatonin is known as a free-radical scavenger. 

The melatonin and other circadian rhythms are shifted during rapid travel across time zones or during shift work when people are subjected to bright lights at night. Within the SCN, cells can adjust rapidly to new time zones or rhythms. However, elsewhere in the body, rhythms in the rest of the cells remain out of sync with the SCN and the phenomenon of jet lag is felt by aircraft pilots and crew.

Those on shift work, even permanent night shift, seldom manage to completely adjust to a nocturnal existance since home activities usually mean that daytime sleep is significantly disrupted. This so-called dual pattern of activity has profound effects on health including hormone problems, mental health problems, stress-related disorders, problems with the immune response and cancers.

 The authors believe that these profound changes in lifestyle, leading to asynchronous circadian rhythms may predispose people such as shift workers to ill health and to cancers in particular. 

South African Journal of Science 2009; 105: 415-420