Working the graveyard shift is known to take a toll on health; shift workers are at greater risk for all sorts of problems, including heart disease, ulcers and obesity. A new study in the journal Current Biology suggests that sleeping in the day and working at night might even increase women’s risk for breast cancer. Researchers took female mice who had been bred to have a high cancer risk and subjected half of them to conditions mimicking shift work. After six days of normal light exposure (12 hours of light followed by 12 hours of darkness), they were kept under the light for 24 hours and their light-dark patterns were reversed the following week. The other half consistently spent 12 hours in the light followed by 12 hours in the dark. The mice whose sleeping patterns were messed with not only gained weight and were less active; they also developed breast cancer eight weeks sooner than the ones who were on a normal schedule.
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