Having a lie-in at the weekend could raise the risk of diabetes and heart disease, say researchers.
Even moderate changes to the time you get up - such as waking early for work in the week or sleeping in on a day off - could lead to ill health.
Researchers have long recognised that shift workers can suffer increased ill-health because of the continual disruption to the circadian system, or natural body clock.
They are more likely to develop heart disease and Type 2 diabetes than employees with regular daytime shifts.
In the latest study, middle-aged individuals who got up at odd times were found to raise levels of fat in blood and reduce a compound that lowers blood sugar levels. The research, published in the Journal of Clinical Endocrinology and Metabolism, is the first to link so-called "social jetlag" in non-shift workers with metabolic illnesses, such as diabetes. Those behind the study said bosses would have to consider the impact of work on sleep and health.
Dr Patricia Wong, of the University of Pittsburgh in the US, said: "Social jetlag refers to the mismatch between an individual's biological circadian rhythm and their socially-imposed sleep schedules.
"This is the first study to show that even among healthy, working adults who experience a less extreme range of mismatches in their sleep schedule, social jetlag can contribute to metabolic problems. These can contribute to the development of obesity, diabetes and cardiovascular disease."
Researchers examined sleep patterns in a group of 447 men and women. They were aged 30 to 54, and they worked at least 25 hours a week outside the home. They wore a wristband that measured their movement and sleep 24 hours a day for a week. Researchers used questionnaires to assess the participants' diet and exercise habits.
Nearly 85 per cent had a later halfway point in their sleep cycle - a measurement known as midsleep - on free days compared to work days. The other 15 per cent had an earlier midsleep on free days than on work days. Participants who had a greater misalignment between their sleep schedules on free and work days tended to have poorer cholesterol profiles, higher fasting insulin levels, larger waist circumference, higher body-mass index and were more resistant to insulin than those who had less social jetlag.
The association persisted even when the data was adjusted to account for physical activity and calorie intake.
Dr Wong added: "We may need to consider as a society how work and social obligations affect our sleep and health.
"There could be benefits to...workplace education to help employees and families make informed decisions about structuring their schedules, and policies to encourage employers to consider these issues."