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“Introduction A number of studies have investigated a possible role of environmental factors in cancer etiology.

One of the factors of particular interest is exposure to light-at-night during the working hours of shift workers, which may cause sleep disruption and altered normal endocrine functions as well as health problems. According to Costa et al. (2010), the data collected in 2005 by the European Foundation for the Improvement of Living and Working Conditions showed that 21.9 % of men and 10.7 % of women work within a shift system that includes evening and night work. Seven per cent of shift workers permanently work at night (European

Foundation for the Improvement of Living and Working Conditions selleckchem 2007). It has been shown that shift work together with the abnormal light–dark cycle connected with it cause adverse health effects. Short-term disturbances in the normal sleep–wake Morin Hydrate cycle give reversible symptoms called a “jet-lag” syndrome (trouble with sleeping, fatigue, lack of appetite). Long-term altered light–night cycle causes chronic sleep deprivation, gastrointestinal and cardiovascular disorders, and adverse pregnancy outcome (Knutsson 2003). In several

recent studies, an increase has been shown in the risk of developing cancer, in particular breast, endometrial and colon cancer, among shift workers (Schernhammer and Schulmeister 2004; Hansen 2006). A review of epidemiological studies devoted to cancer risk in shift workers performed by Kolstad (2008) and Pauley (2004) demonstrated 36–60 % higher rates of breast cancer risk among this population. In 2007, the International Agency for Research on Cancer classified night shift work as a probable carcinogen (group 2A), based on limited evidence from human studies and adequate evidence from animal selleck compound experiments (Straif et al. 2007). Light exposure during night hours changes melatonin secretion and can disrupt the human circadian rhythm via melatonin secretion (Mirick and Davis 2008). A circadian rhythm disruption induces altered endocrine functions—possible changes in the regulation of reproductive hormone receptors—and thus it is an important factor in the etiology of hormone-related diseases, for example, breast or prostate cancer (Mirick and Davis 2008; Grant et al. 2009).