Irregular sleeping patterns have been “unequivocally” shown to lead to cancer in tests on mice, a study suggests.
The report, in Current Biology, lends weight to concerns about the damaging impact of shift work on health.
The researchers said women with a family risk of breast cancer should never work shifts, but cautioned that further tests in people were needed.
The data also indicated the animals were 20% heavier despite eating the same amount of food.
Studies in people have often suggested a higher risk of diseases such as breast cancer in shift workers and flight attendants.