Doing the night shift throws the body “into chaos” and could cause long-term damage, warn researchers.
Shift work has been linked to higher rates of type 2 diabetes, heart attacks and cancer.
Now scientists at the Sleep Research Centre in Surrey have uncovered the disruption shift work causes at the deepest molecular level.
Experts said the scale, speed and severity of damage caused by being awake at night was a surprise.
The human body has its own natural rhythm or body clock tuned to sleep at night and be active during the day.
It has profound effects on the body, altering everything from hormones and body temperature to athletic ability, mood and brain function.
The study, published in Proceedings of the National Academy of Sciences, followed 22 people as their body was shifted from a normal pattern to that of a night-shift worker.