That ideas has now gone mainstream:
Night shifts spark cancer pay-out
The Danish government has begun paying compensation to women who have developed breast cancer after long spells working nights. It follows a ruling by a United Nations agency that night shifts probably increase the risk of developing cancer
...... there was evidence to support the hypothesis that alterations in sleep patterns could suppress the production of melatonin in the body.
"Melatonin has some beneficial effects in preventing some of the steps leading to cancer," he said. "The level of evidence is really no different than it might be for an industrial chemical."
I'm off to bed.....