Recent Study Connects Working Night Shifts With Increased Breast Cancer Risk

Shiftwork that involves disrupting the circadian rhythm (natural sleep patterns) probably causes cancer, according to IARC. Photo by: opnurse

recent breast cancer study found that working the night shift can increase a woman’s chances of developing breast cancer.

The journal Occupational and Environmental Medicine published a study that may confirm a relationship between night shift work and an increase in breast cancer risk as much as 40% higher then a day shift worker. The study agrees with IARC’s placement of night shift work on their carcinogens list as “probably carcinogenic to humans.”

According to the article, there may be a connection between melatonin production, which is regulated by daylight and nighttime, and estrogen production.

From the Journal of the National Cancer Institute:

Exposure to light at night may increase the risk of breast cancer by suppressing the normal nocturnal production of melatonin by the pineal gland, which, in turn, could increase the release of estrogen by the ovaries. This study investigated whether such exposure is associated with an increased risk of breast cancer in women.

The studies have found that if you work two night shifts or less per week your risk is not increased. The level of risk was influenced by whether the test subject considered themselves to be a “morning person” or a “night person.” Depending on these factors it is apparent that those working the night shift opposite to their natural rhythms were more disturbed by changes to the body’s internal clock.

Additional breast cancer risk factors faced by night workers may also contribute to a higher incidence of breast cancer.

WebMD published an online article about the possible link:

The night workers in the new study tended to sunbathe more frequently than their counterparts who worked by day. This observation does not support the theory that the increased breast cancer risk among night shifters was due to less sun exposure.

Several studies suggest that night-workers have a higher incidence of breast cancer—as well as an association with more risk factors for breast cancer (e.g. obesity, smoking, alcohol use),” says Marisa Weiss, MD, via email.

Do you work the night shift? What are your thoughts on this new study? How has your working schedule effected your health?