Before you brush aside your alarm clock for the weekend, you may want to rethink any extended morning snoozes (however glorious they may be).

Sleeping late on days-off—and other sleep-time adjustments—are linked to metabolic problems, including insulin resistance and a higher body mass index, according to a new study published in the Journal of Clinical Endocrinology & Metabolism. The finding suggests that regular sleep shifts could rouse long-term health problems such as cardiovascular disease and diabetes, the authors conclude.

Though other research has connected sleep disruptions to poor health, the new study is the first to specifically link shifts in dozing times to metabolic problems. Those problems were independent of other factors such as sleep disorders, smoking, and socioeconomic status.

Such weekly sleep changes may alone cause trouble by throwing off the body’s internal clocks, putting metabolic cycles out of sync with other circadian rhythms, the authors speculate. For instance, fat accumulation in tissues, food absorption in the gut, and insulin secretion in the pancreas and liver all show tissue-specific circadian rhythms, the authors note.

To catch the effects of adjusting sleep times, the researchers (led by Patricia Wong at the University of Pittsburgh) tracked the health, sleep habits, and diets of 447 middle-aged, healthy people during a seven-day study. For the whole study, participants had to wear a motion-monitoring wrist accelerometer, called Actiwatch-16, so that researchers could record their precise shut-eye schedules.

Wong and colleagues also made sure that the monitoring period for each participant included at least one night before a day-off. This allowed researchers to note workday and play-day sleep schedule differences or what scientists have come to call “social jet lag.”

None of the participants maintained their workday sleep schedules on days-off, the researchers found. Based on the midpoint of each participant’s sleep times, about 85 percent of the participants shifted their sleep time forward—sleeping in—with the remaining 15 percent shifting earlier. Overall, the participants had a mean shift of 44 minutes forward, with only a small number of participants shifting their sleep by two or three hours in either direction.

Some of the participants appeared to be sleeping longer on weekends to compensate for sleep debt during the week, the researchers noted. And sleep debt also linked to health problems.

Generally, the bigger the difference between workday and free-day sleep schedules, the stronger the link to metabolic health problems, the researchers found. More social jet lag aligned with more fats in the blood, more insulin resistance, bigger waist circumference, higher body mass index, and lower HDL-cholesterol (“good” cholesterol). The link remained after the researchers adjusted for health factors such as exercise, calorie intake, alcohol use.

Journal of Clinical Endocrinology & Metabolism, 2015. DOI: 10.1210/jc.2015-2923 (About DOIs).