5. Shift Work
The only non-tangible to make the top 20, shift work has been linked to cancer in a series of studies -- but science has yet to make a definitive connection.
The culprit is thought to be interference with biological circadian rhythms, wherein humans are exposed to light during periods of darkness. A 2007 study in the Lancet noted that shift work "involves circadian disruption [that] is probably carcinogenic to humans."
Where will you find it? At all-night grocery stores, hospitals, factories and homes with newborns across the country. An estimated 15 percent of us are earning our keep doing shift work, according to estimates in the ACS report.
How can you avoid it? Not easily, if your livelihood depends on it, though it does give new meaning to "Don't quit your day job."
Gulp!!!!



