It's practically a law of nature: If you stay out late on Friday night, you'll feel it on Saturday morning. But a new study [PDF] published in the journal Sleep suggests the repercussions of partying on the weekends last long after Monday morning rolls around. As Medical News Daily reports, “social jet lag"—what happens when someone goes to bed later on weekends than during the week—has a negative impact on overall wellbeing.

For the study, researchers looked at 984 people between the ages of 22 and 60 who responded fully to a Sleep Timing Questionnaire. Participants were asked report their sleep habits and rate their health as “Excellent," "Good," or "Fair/Poor."

They found that inconsistent sleep schedules can lead to several issues, such as fatigue and irritability. The lifestyle is connected to more serious problems as well: For every hour of social jet lag accumulated, subjects were 11.1 percent more likely to develop heart disease. People who racked up just one hour of social jet lag had a 28 percent higher chance of describing their health as ”Fair/Poor" instead of “Excellent.”

Even if you sleep until noon after getting home at 4 a.m., that won’t necessarily remedy the problem. Previous studies have shown that disrupting your circadian rhythm, even if you make those hours up eventually, has nasty effects on your metabolism. So if you work a nine-to-five job during the week, you should probably stick to a reasonable bedtime on the weekends.

[h/t Medical News Daily]