Canadian researchers studying breast cancer have found that the risk of developing the disease doubles after a woman works night shifts for at least 30 years. Their work expands research confined to the effect of shift work on healthcare workers.
Several earlier studies suggested a correlation between , according to ScienceDaily. However, some experts questioned the relationship due to the potential failure of the research to properly assess exposure and to include sufficient diversity in patterns of shift work.
The National Cancer Institute estimates thatin 2013. Nearly 40,000 will succumb to it the same year.
The Canadian scientists selected 1,134 women with breast cancer and 1,179 without the disorder for their study. The women were all the same age and lived in either Vancouver, British Columbia, or Kingston, Ontario. They provided detailed information about shift work over their entire history of employment.
Hospital records provided information on the type of tumor each breast cancer subject had. The researchers considered this information important because sensitivity to hormones can alter risk factors for the disease. In particular, alteration in the amount of melatonin has been associated with raising estrogen production and elevating breast cancer risk among individuals who work night shifts.
Melatonin, often called a , occurs naturally in the human body, according to MedlinePlus. Some individuals also take melatonin supplements to regulate their internal body clocks. Common uses include treating jet lag and adjusting sleep-wake cycles in individuals with changes in their work schedules.
Women who had worked night shifts made up about a third of all subjects. Among those with this schedule for up to 14 years and for those who had worked the night shift for 15 to 29 years, the researchers noted no elevated risk. However, women who had worked the night shift for at least 30 years were twice as likely to have developed breast cancer.
Results were similar for women who were healthcare workers and those who had not worked in that field. Women whose tumors were estrogen- and progesterone-sensitive also faced higher risk factors.
The researchers, who published their findings in the journal Occupational and Environmental Medicine, indicate that while melatonin is cited as the cause of a link between breast cancer and shift work, other factors could play a role. Among them are out-of-sync body rhythms, sleep disturbances, vitamin D levels, and lifestyle differences. An important conclusion of the study is that if decades of night shifts double breast cancer risk for some women, there is a need to develop healthy workplace policy.
Vonda J. Sines has published thousands of print and online health and medical articles. She specializes in diseases and other conditions that affect the quality of life.
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