A new study conducted by researchers in Denmark has found that regularly working on night shifts can increase the risk of breast cancer by as much as four times in women.
The study, published in the journal Occupational and Environmental Medicine, was based on questionnaires from 692 women of whom 141 were diagnosed with breast cancer.
The researchers found that those who regularly worked on night shifts were 40 percent more likely to develop the cancer.
"The results indicate frequent night shift work increases the risk for breast cancer and suggest a higher risk with longer duration of night shifts. Those with morning preference tended to have a higher risk than those with evening preference", lead researcher Dr Johnni Hansen, of the Danish Cancer Society, said.