Artificial light
<p>The World Health Organization in 2007 named late night shift work as a probable cancer-causing agent.<sup id="cite_ref-pmid19271347_69-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-pmid19271347-69" >[70]</a></sup><b> </b><b>Melatonin is an anti-oxidant and suppressant of tumor development that is produced at night; when someone works in artificial light, they generally have lower melatonin and may be more likely to develop cancer.</b> Melatonin supplements may simulate the melatonin production at different times that does not occur during regular sleeping hours for people who work night shifts.<sup id="cite_ref-pmid19271347_69-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Melatonin#cite_note-pmid19271347-69" >[70]</a></sup></p>