As reported by the Arizona Republic, January 10, 2007.

Late Nights Confuse Hormone Processes

By Susan Brink, Los Angeles Times Reporter

Some cancers might be rooted in sleep deprivation - or, more precisely, to too many hours exposed to artificial light, according to Richard G. Stevens, cancer researcher at the University of Connecticut Health Center.

His work is based on the theory that the increase in breast cancer in the industrialized world is linked to the disruption of hormone cycles.

Light, he says, suppresses production of the hormone melatonin, which allows levels of estrogen to rise. And, when lights are on long after dark, it confuses women's circadian clocks, the roughly 24-hour internal rhythm that keeps hormones and organs on their daily schedule.

"Cells don't know when not to divide," he says.

His theory was bolstered by a 1991 Centers for Disease Control and Prevention report showing that blind women are about half as likely as sighted women to get breast cancer.

An Oct. 15, 2005, study in Cancer Research looked at sleep patterns of more than 12,000 women. Although researchers found no statistically significant increase in cancer risk among short sleepers, says Stevens, an author of the study, the risk estimates were consistently lower in long sleepers.

Until more is known, he advises women to get adequate sleep - and to do it in a very dark room.