Irregular sleeping patterns have been conclusively shown to lead to cancer in tests on mice.

A new study, published in the journal Current Biology, adds to prior studies that have noted the damaging impact of shift work and poor sleeping patterns on health, BBC News reports.

The researchers said the findings suggest women with a family risk of breast cancer should never work shifts.

Researchers speculate that poor sleep disrupts the body's internal biological clock, lowering immune system function and increasing the risk of disease.