Women who work on night shifts have an increased risk of developing multiple common cancers, especially breast cancer, researchers from China say.

Ma Xuelei, a tumor scientist at Sichuan University, and his colleagues have performed an analysis using data from 114,628 cancer cases involving 3,909,152 people from North America, Europe, Australia, and Asia.

The study concludes that overall, long-term night shift work among women increases the risk of cancer by 19%.

The photo shows single mother Li Shaoyun sitting in a taxi with her three-year-old daughter in her arms. Li is a taxi driver in central Chinese city of Wuhan. She only works at night. Following her divorce two years ago, she has been working at night while at the same time taking care of her daughter. [Photo: www.dfic.cn]

When it comes to specific cancers, the researchers has found that this group has an increased risk of skin (41%), breast (32%), and gastrointestinal cancer (18%) compared with women who do not perform long-term night shift work.

After stratifying her cases by location, Ma has found that an increased risk of breast cancer is only found among female night shift workers in North America and Europe.

"We were surprised to see the association between night shift work and breast cancer risk among women in North America and Europe," said Ma. "It is possible that women in these regions have higher sex hormone levels, which are usually associated with hormone-related cancers such as breast cancer."

A further study has looked specifically at long-term night shift work and risk of six types of cancer among female nurses.

They have found that those who work the night shift have an increased risk of breast (58%), gastrointestinal (35%), and lung cancer (28%) compared with those that did not work night shifts.

Nurses are said to have the highest risk of developing breast cancer if they work night shift.

The researchers have also found that the risk of breast cancer increase by 3.3% for every five years of night shift work.

"Night shift, as a current social phenomenon, is becoming common. However, it can have adverse effects on health," Ma said.

Ma advises long-term night shifters to regularly receive tumor screening.