Shift work is more likely to give you cancer, according to new research.
The study, published in Current Biology, claims that irregular sleeping patterns “unequivocally” led to breast cancer in mice.
Although scientists cautioned that the results needed further tests on human, they said women with a history of breast cancer should never work shifts.
The findings support previous research that has suggested health dangers linked to working irregular hours, such as shift workers or flight attendants.
Scientists have suggested that by disrupting the body’s internal clock – known as the circadian rhythm disturbance (CRD) – increases the chances of getting cancer.
However, researchers have been unable to find causal evidence to support their theory, with many suggesting the link may be because of factors such as social class, activity, or vitamin D levels.
The latest study, which used mice, circumvents some of the problems associated by examining humans for this theory and found that mice who had their body clock delayed by 12 hours every week for a year showed a “decrease in tumour suppression.”
The animals, who are prone to breast cancer, usually develop tumours after 50 weeks – but circadian disruption meant scientists found tumours eight weeks before that.
"This is the first study that unequivocally shows a link between chronic light-dark inversions and breast cancer development," the report claims.
An additional finding was the mice under these pressurised situations put on more weight than mice in the control group.
Researcher Gijsbetus van der Horst, from the Erasmus University Medical Centre, in the Netherlands, said: "If you had a situation where a family is at risk for breast cancer, I would certainly advise those people not to work as a flight attendant or to do shift work".