Social jet lag study: students' body clocks swing 85 minutes each weekend

A study of 243 university students in Fortaleza, Brazil, published in the journal Frontiers in Public Health around 12 November 2026, found that most of the young adults slept poorly, tended to be "night owls" and lived with social jet lag, a weekly mismatch between their body clock and their timetable, averaging about 1 hour 25 minutes. The researchers, led by Teles and colleagues, said their results point to links between body rhythms, sleep, diet and early risk factors for heart disease, even in a young group that looked healthy.

Social jet lag is a simple idea with a technical name. On weekdays, classes, work and commuting decide when a student sleeps and wakes. On weekends, people sleep on their own clock, usually later. The gap between the two, measured as the difference in the midpoint of sleep, is called social jet lag because it feels like flying across time zones and back every week, without leaving home.

For students and first-jobbers, this pattern is familiar: late nights with phones and screens, early lectures or shifts, and long lie-ins on Sunday. The Brazilian study adds to research suggesting that this weekly swing is not harmless. Its authors found that poor sleep, late body clocks and social jet lag went together in their group of young, apparently healthy students, and that these sleep patterns were tied to diet and to early markers of cardiovascular risk.

The limits matter. The study took one snapshot of 243 nutrition students in one Brazilian city, so it cannot show that social jet lag causes heart problems, only that the two appear together. Students of nutrition may also eat differently from others. Readers should see the findings as a signal worth noting, not as proof, and the study offers no medical advice. Anyone with persistent sleep problems should speak to a qualified doctor.

What it means in daily life is fairly practical and widely discussed in sleep research: keeping sleep and wake times similar across weekdays and weekends reduces social jet lag by definition, because social jet lag is the difference between the two.

Peepals calculation: An average social jet lag of 1 hour 25 minutes is 85 minutes (60 + 25). That is like shifting about 1.4 time zones every weekend and back again on Monday (85 ÷ 60 ≈ 1.42). Over a year of 52 weekends, that adds up to about 74 hours of back-and-forth clock shifting (85 × 52 = 4,420 minutes ≈ 73.7 hours). Our calculation from the reported figures.

Short-term: The study adds evidence that poor sleep and late body clocks are common among university students, a group often left out of heart-health research.

Long-term: If larger studies over time confirm the link between social jet lag and cardiovascular risk, colleges and employers may face more pressure to consider schedules, such as very early classes, that clash with young people's body clocks.

Who is affected: University students and young workers with irregular sleep; colleges planning timetables; and researchers studying how lifestyle in the late teens and twenties shapes later health.

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