Adults typically need seven to nine hours of sleep each night to feel fully rested and function at their best. (1) , Americans are getting less sleep than they did in the past. A 2005 National Sleep Foundation poll found that Americans (2) 6.9 hours of sleep per night, which represents a drop of about two hours per night (3) the 19th century, one hour per night over the past 50 years, and about 25 minutes per night just since 2001. (4) , we are not very good at perceiving the (5) effects of sleep deprivation. Researchers at the University of Pennsylvania restricted (6) to less than six hours in bed per night for two weeks. The volunteers (7) only a small increase in sleepiness and thought they were (8) relatively normally. However, formal testing showed that their cognitive abilities and reaction times (9) declined during the two weeks. By the end of the two-week test, they were as (10) as subjects who had beer awake (11) for 48 hours. A. while B. since C. unless D. once
A recent review by a team from Case Western Reserve University and Harvard Medical School found that all of the large studies that followed people over time agreed that short sleep duration was (12) with future weight gain. This connection was (13) strong in children: all 31 studies in children showed a strong association between short sleep (14) and current and future obesity. (15) , a study by Susan Redline and colleagues showed an opposite (16) between sleep duration and obesity in high-school-age students. The shorter the sleep, the higher the (17) of being overweight We have many opportunities to avoid sleep—lights, electronic devices, and other entertainment offer round-the-clock (18) . But we must recognize the importance of sleep and make it a(n) (19) to get enough. It is a lot easier to prevent weight gain by getting enough sleep than it is to treat the problem (20) it develops.