Sleep expert David Earnest often tells college students that a good night's sleep is important for academic success.

　　Not that they listen to him.

　　Earnest is a professor at Texas A&M College of Medicine. He explains that so-called "all nighters," in which students spend all night studying instead of sleeping, are not effective – or healthy.

　　"The sort of common approach for college students...is to wait until the last minute in terms of preparing or studying for an exam -- do all nighters, especially before final exams. Because that way, you can cram all of your studying into a very short period of time."

　　"But in the process obviously that compromises sleep and unfortunately it's counterproductive."

　　Waiting until last minute

　　College students often wait until the last minute to review information and study for an exam. They may stay up all night ahead of the test.

　　Research shows, however, it is not worth it. Earnest explains that people who stay up all night do not remember as much about what they read or studied. There is also some evidence that people even suffer temporary drops in their IQ, or intelligence quotient, he said.

　　If a student must prepare for an exam at the last minute, Earnest suggests studying until about 2 a.m., sleeping for four hours, and then reviewing the material again early in the morning.

　　Four hours is not enough sleep, but it is better than no sleep, Earnest said.

　　Company uses device to measure student sleep

　　Jawbone is a company that sells a small device that people attach to themselves to measure exercise and sleep. The company used information from device users to measure how much time college students sleep.

　　It found that college students slept an average of 7.03 hours during the week and 7.38 hours on weekends. Female students slept more than male students; they get an extra 23 minutes of sleep on week nights and 17 more minutes on weekends.

　　Jawbone's study seems to suggest that college students are getting enough sleep. The numbers are within the numbers suggested by the National Sleep Foundation. It recommends between seven and nine hours of sleep daily for people aged 18 to 25.

　　But Jawbone said the "average" hours of sleep in its study can be misleading. Its study also found that nearly half of the time, students get less than seven hours of sleep a night.

　　Jawbone also found some other interesting sleep information.

　　Students at America's military academies, West Point, the Naval Academy and Coast Guard Academy, all require students to get up before 7 a.m. That is the earliest required waking time for college students. As a result, students at the three schools average 6.38 hours of sleep, the lowest among American college students.

　　Other colleges where students average less than seven hours of sleep on weeknights include Columbia University in New York, the University of Notre Dame in Indiana and Case Western Reserve University in Ohio.

　　Students at the University of New Hampshire, the University of Oregon and the University of San Diego got the most sleep, Jawbone said.

　　2014 report finds sleep problems for many students

　　A 2014 report for the US National Library of Medicine and National Institutes of Health reported that daytime sleepiness and irregular sleep schedules are common among college students.

　　The report said a lack of sleep can result in lower grade point averages. It also found it can lead to increased risk of academic failure and of emotional distress.

　　The National Sleep Foundation offers suggestions for better sleep:

　　1.Go to bed at the same time each night and wake up at the same time in the morning.

　　2.Make sure your bedroom is a quiet, dark, and relaxing environment, and that it is neither too hot nor too cold.

　　3.Make sure your bed is comfortable, and that you do not use it for other activities such as reading, watching television or listening to music.

　　4.Remove all TVs, computers, radios, and telephones from the bedroom.

　　5.Avoid large meals before bedtime.

　　Here's wishing you a good night's sleep!

　　I'm Bruce Alpert.

　　And I'm Jill Robbins

　　Bruce Alpert reported on this story for VOA Learning English. Ashley Thompson was the editor.

　　We want to hear from you. Write to us in the Comments Section and share your experiences on 51VOA.COM. Do you get enough sleep? If you don't, how does it affect you? And what's your "secret" to falling asleep quickly?