Canadian researchers compared the self-reported work history of 1,134 women with breast cancer and 1,179 women without the disease and found that post-menopausal women with more than 30 years of night shift work under their belts had a higher risk of the disease than their peers even when taking factors like family history and menopausal status into account. Previous studies found higher rates of breast cancer in health care employees who worked night shifts for decades, but this study, which included women who held jobs in a variety of fields, points to long-term sleep disruption as the common offender. What’s so horrible about being nocturnal? Experts believe exposure to light at night could depress production of melatonin, a hormone thought to ward off cancer. Another theory is that clock genes, which control the circadian rhythm and help regulate cell cycles, might be thrown off, facilitating the growth of cancerous tumors. “In this study we weren’t able to specifically examine any of these mechanisms,” says Anne Grundy, PhD, coauthor of the joint study between the Department of Public Health Sciences and Queen’s Cancer Research Institute at Queen’s University in Canada. “Melatonin interference is the pathway that sees the most attention in the literature so far, but it may be more complex.” Other theories propose that night shift workers’ diet and exercise habits suffer leading to poorer overall health and higher risks of the disease, or that these women simply don’t clock as much sleep as women who work during waking hours. Although the jury’s still out on exactly what’s harming late-night workers, Dr. Grundy says women who currently work night shifts can take small steps to lower their risk simply by sticking to healthy diet and exercise habits and minimizing light sources when they snooze during daylight hours. For the rest of the population, pulling the occasional all-nighter shouldn’t pose a threat. “We saw that it’s the long-term shift work that’s having an effect,” Dr. Grundy says. “If you’re occasionally having to stay up all night to do other things, it’s probably not going to be a very big deal.”
