Irregular sleep tied to worse grades

College students who go to sleep and wake up at different times during the week may be harming their academic performance, according to a US study.

Consistency — going to bed and waking up at about the same time every day, weekends included — was linked with a better grade point average (GPA) among the college students in the study, the researchers found. 

“College students who sleep starved themselves during the week and then binge slept on weekends had poorer grades than those whose schedules were more consistent,” senior author Dr Charles Czeisler, director of the Sleep Health Institute at Brigham and Women’s Hospital in Boston, told Reuters Health by e-mail. 

Importantly, it didn’t matter how much sleep the students got overall. Sleep timing on its own could predict worse academic performance, even if students made up for lost night-time sleep with naps during the day, according to the results published in Scientific Reports.

Czeisler and colleagues studied 61 full-time undergraduates ages 18 to 24 for 30 days. Students completed sleep diaries and the researchers used the Sleep Regularity Index (SRI), a tool they developed, to evaluate the students’ sleep patterns. The index is scaled so that someone who sleeps and wakes at exactly the same time each day scores 100, and someone who sleeps and wakes at random times scores 0.

Those who scored in the top 20 per cent were classified as regular sleepers and those who scored in the bottom 20 per cent were irregular sleepers. 

Both groups averaged about seven hours of sleep daily, though irregular sleepers reported poorer sleep quality. 

Regular sleepers were asleep 55 per cent of the “clock night” — the hours between 10pm and 10am — and only 1 per cent of the clock day, whereas irregular sleepers slept for 42 per cent of the clock night and 11 per cent of the clock day.

As a result, irregular sleepers experienced significantly less daytime light and relatively more light at night, which triggered a delay in secretion of the sleep hormone melatonin in the body, according to the researchers.

These differences led to a body clock shift in irregular sleepers equivalent to traveling west for almost three hours, Czeisler said, which could explain their poorer academic performance. “For students whose sleep and wake times were inconsistent, classes and exams scheduled for 8am were occurring at 5am body time — a time when cognitive performance is impaired,” he said.

Greater sleep regularity was associated with better GPAs. Every 10-point increase on the sleep regularity index was associated with an average increase of 0.10 points in GPA. At the end of the study, irregular sleepers averaged GPAs of about 3.24 out of a possible 4.0, and regular sleepers averaged 3.72.

The study doesn’t prove that irregular sleep causes poorer academic performance, the researchers note, but it could be a sign of other daily habits that interfere with how well students do in college. 

Increasing exposure to daytime light and decreasing exposure to laptops and other light-emitting devices before bedtime might improve sleep regularity, they suggest.

Sleep specialist Dr Rafael Pelayo of the Stanford Sleep Medicine Centre in California told Reuters Health that while it’s possible some people handle sleep deprivation better than others, many students may be underperforming and not realise it.

“I compare it to having a race car,” Pelayo said. “The manufacturer may recommend high-octane gas, but you can put cheap gas in it and if you’re stuck in traffic, you won’t notice a difference. But if you put it on a race track, you will. The real question is, ‘Could you do better academically if you had better quality sleep?’”

Typically, students say when they go to bed or wake up depends on what day it is. When they’re on different schedules every other day and on the weekend, Pelayo noted: “The brain gets thrown off. It’s like always being jetlagged — you’re never quite at your best.”

Instead, he advises, pick the earliest time you have to wake up, and make that your default wakeup time for the whole week. Do the same for bedtimes. “Do that for several weeks to get into a rhythm, because making your sleep predictable is going to make you feel better and do better.”