By Jimmy Downs

Sunday Sept 16, 2012 (foodconsumer.org) -- Women ever working night shifts face a drastically increased risk of breast cancer, compared to those who never work at night, according to a new study in Occupational and Environmental Medicine.

Johnni Hansen and Christina F Lassen at Institute of Cancer Epidemiology, Danish Cancer Society in Copenhagen, Denmark conducted the case-control study and found women who ever worked night shifts were 40 percent more likely to develop breast cancer, compared to those who never worked night shifts.

A total of 18, 551 female military employees born in 1929 to 1968 were followed and of them 218 women were diagnosed with breast cancer during the period of 1990 to 2003.  The cases were compared with 899 age-matched controls from the same cohort.

The association between night shift work and risk of breast cancer was dose-responsive, that is, increasing number of years of night shift work and cumulative number of shifts were correlated with increasing risk for breast cancer. However, a neutral risk was found for fewer than three night shift per week.

Women who had highest cumulative exposure to night shift work was more than twice as likely as those who had the lowest cumulative exposure to be diagnosed with breast cancer.

The highest increase in the risk due to night shift work was found in those with morning chronotype preference and intense night shifts.  Their risk for breast cancer was nearly four times as high as others'.

The researchers concluded "The results indicate that frequent night shift work increases the risk for breast cancer and suggest a higher risk with longer duration of intense night shifts. Women with morning preference who worked on night shifts tended to have a higher risk than those with evening preference."

Night shift work has been recognized as a probable human carcinogen. Those who are at higher risk of breast cancer are advised to avoid doing night shift work.

Breast cancer is expected in 230,000 women in the U.S. in 2012 and the disease and its complications are expected to kill nearly 40,000 women in the same year in the U.S., according to the National Cancer Institute.

Breast cancer is in many cases preventable by following a healthy lifestyle including a healthy diet.  An authoritative organization says evidence is strong that medical radiation used in diagnostic tools like mammography and hormone therapy can increase the risk of the disease greatly.