In our busy 24-hour world, Americans are devoting far less time
to sleep. In 1910, Americans slept an average of nine hours per
night. In 1975, that number fell to 7.5 hours. It dropped to 6.8
hours in 2005. According to the National Heart, Lung and Blood
Institute, one in six people in the United States averages less
than six hours of sleep per night. Insufficient sleep has been
associated with depression, irritability, behavior problems in
children and friction in relationships. Relatively minor
decreases in sleep time decrease performance on tests that
measure memory, concentration and the ability to complete simple
tasks and also increase risk of accidents, including car crashes
and work injuries. We are now learning that there are also
consequences to our physical as well as mental health from
getting too little sleep. • Heart disease: In 2011, researchers
at the University of Chicago scanned for calcium deposits in the
coronary arteries, a marker for hardening of the arteries, in
495 middle-aged adults