We’ve got some bad news: Sleeping a few extra hours on the weekend may actually be bad for you. In effect, by spending a few additional hours in the land of dreams, you are giving yourself “social jet lag,” according to a new study published in the Journal of Clinical Endocrinology and Metabolism. This, they say, can lead to health problems in the long run.

Circadian rhythms, which are also found in plants, animals, fungi and some bacteria, allow organisms to coordinate their biological activity with the day-night cycle. Although this rhythm is “built-in,” it is adjusted to the local environment using zeitgebers (“time givers”), external clues like temperature, light levels and so on.

By changing our sleeping patterns over a short period of time, we are causing our natural rhythm to become out of sync with the surrounding zeitgebers, which in effect is what jet lag is. This new study aimed to investigate this phenomenon in a non-invasive way, allowing the subjects to live their normal lives while the researchers unobtrusively monitored their sleep patterns.

Over the course of the research, 447 people’s sleep patterns were tracked using sleep monitors attached to their wrists, which estimated sleep time based on the movement – or lack thereof – of the participants. Their health status was also assessed, and several blood samples were taken throughout the study. In particular, the researchers were looking for changes in blood sugar and cholesterol levels.

As expected, participants’ sleep patterns changed over the weekend, with many of the subjects staying up later and sleeping for longer. Worryingly, the researchers found an apparent correlation between this shift in sleeping pattern and the appearance of markers of detrimental health effects. The more dramatic the weekend shift was, the more likely the subject was to show lower levels of “good” cholesterol and higher amounts of triglycerides (other fatty substances) in their blood – precursors to heart disease in the long term.

^{Image credit: Sleeping in on the weekends may be messing up your internal clock. cosma/Shutterstock}

Those with a more dramatic shift were also the most likely to experience weight gain and exhibit symptoms associates with the onset of diabetes. Although this study did not show that anyone developed heart disease or diabetes, it does imply that sleeping in and staying up far later on weekends, and then switching back to a normal weekday work pattern, may eventually have a negative effect on your health.

However, the study did have some limitations: In particular, the researchers did not explore whether participants with greater social jet lag had different circadian rhythms than those with less. This means that certain people’s own circadian rhythms may have been more suited to the weekend sleeping pattern, whereas others’ may have been more compatible with the weekday sleep schedule.

A similar study, albeit more invasive, was conducted in 2012 by Harvard University. In this instance, the subjects were locked in a laboratory for several weeks, and were only allowed 5.6 hours sleep a night on a 28-hour-long day. Without a doubt, the most significant detrimental effect was to the subjects’ metabolism, their ability to convert nutrients into energy.

At the beginning of the study, all the participants were physically healthy; by the end of it, three were beginning to show signs of “prediabetes,” in that they had incredibly high sugar levels that the body was almost unable to reduce. The others were progressing rapidly towards this state.

Sleep disruption is already known to increase the likelihood of getting heart disease, diabetes and obesity; this new study, along with others, implies that by snoozing in for longer on the weekend, we are effectively causing our own circadian misalignment – and risking our health as a result.