Their theory that artificial light can cause breast cancer is simple. Prolonged periods of exposure to artificial light disrupt the body's circadian rhythms - the inner biological clocks honed over thousands of years of evolution to regulate behaviors such as sleep and wakefulness. The disruption affects levels of hormones such as melatonin and the workings of cellular machinery, which can trigger the onset of cancer, Stevens theorizes.

"Mankind has only been exposed to these light sources for 150 years or so," Stevens said.

So far, the theory is based largely on suggestive, but inconclusive, observational studies. For instance, night-shift workers such as nurses tend to be more prone to develop breast cancer than day-shift workers, and blind women are less likely to have breast cancer than women with sight.

# posted by Gerry Canavan @ 4:29 PM  |