30 Years of Night Shift Work Doubles Risk For Breast Cancer

By Dr. Kathleen Ruddy

Several studies involving nurses whose careers typically involves shift work have suggested that an irregular work schedule, particularly if the work disrupts normal sleep patterns, may increase the risk for breast cancer. Because other professions such as air traffic controllers and public safety officers often involve shift work, researchers in Canada wanted to investigate the broader association between fluctuating work schedules and the risk for breast cancer.

How many women were involved in the study?

A group of 2313 women in Canada, (Vancouver, British Columbia, and Ontario) whose jobs involved night shift duty were studied to examine the relationship between night shift duty and the risk for breast cancer. Within this group, there were 1134 who were breast cancer survivors and 1179 otherwise healthy women.

What were the results of the study?

Researchers in Canada found that women who worked any type of job that involved night shift work for more than 30 years had a markedly increased risk for breast cancer. Women who worked night shifts for less than 30 years appeared to have no increased risk for breast cancer.

DID YOU KNOW?

Estrogen receptors are proteins that allow estrogen, a hormone made and secreted primarily by the ovaries, to move from the bloodstream into the cells of the breast. Scientists have found that women who work night shifts for more than 30 years have a increased risk for breast cancer tumors that express estrogen receptors.

How much did night shift work increase the risk for breast cancer?

Women who worked night shifts for more than 30 years had twice the risk of breast cancer compared to other women.

What factors might contribute to the increased risk for breast cancer in night shift workers?

Night shift work disrupts the body’s normal sleep/wake cycle and the hormones, such as melatonin and glucocorticoids, that regulate this cycle. Researchers have discovered that when melatonin is altered by night shift work, there is a compensatory rise in estrogen levels. Estrogen is a female sex hormone that is known to increase the risk for breast cancer, thus it is hypothesized that the elevation of estrogen observed in night shift workers may contribute to their increased risk for breast cancer.

Women whose jobs involved working night shifts for more than 30 years have twice the risk for breast cancer compared to other women. Night shift work alters the normal sleep/wake cycle and disturbs the hormones, such as melatonin, that control this cycle. When melatonin levels are altered, there is a corresponding elevation in the production of estrogen, which may explain why women who work night shifts for more than 30 years have both an increased risk for breast cancer and an increased risk for tumors that express estrogen receptors.

If you’d like to receive more information about breast cancer and what the Breast Health and Healing Foundation is doing to battle the disease, please sign up for our newsletter. You can sign up here: http://breasthealthandhealing.org/im-in/.