Three years ago, investigators at Fred Hutchinson Cancer Research Center made headlines nationwide when they published the results of a population-based study that suggested women who work the graveyard shift have an increased risk of breast cancer as opposed to women who work the day shift.
Now, the researchers are taking their investigation one step further by launching the first study of its kind to measure the influence of night-shift work on hormone levels that may affect breast-cancer risk.
More than 300 female Seattle-area hospital and laboratory shift workers are needed for this National Cancer Institute-funded study, led by Scott Davis, Ph.D., a member of Fred Hutchinson's Public Health Sciences Division.
"There is evidence that shift work may increase the risk of developing breast cancer, and perhaps have other impacts on health as well," Davis said. "It is important to identify the biological mechanisms that may be responsible for such effects so that strategies might be developed to reduce risk in the future."
Davis and colleagues hypothesize that the increased risk in breast cancer they've observed among night-shift workers is most likely due to disruptions in the sleep/wake cycle and exposure to light at night, both of which may affect endocrine function and the regulation of reproductive hormones implicated in the development of breast cancer.
One theory, Davis said, is that nighttime sleep deprivation or exposure to light at night somehow interrupts the production of melatonin, a hormone produced at night by the brain's pineal gland. Melatonin production in turn prompts the ovaries to make extra estrogen — a known hormonal promoter of breast cancer.