Sleep: Getting too much or too little?

Most of us feel like we don’t get enough sleep. But what exactly is enough? And regardless of how much we get, just how good is our sleep?

On 13 June 2011, in Minneapolis, Minnesota, Ron Grunstein, Professor of Sleep Medicine at the University of Sydney, will receive the prestigious Nathaniel Kleitman Distinguished Service Award from the American Academy of Sleep Medicine.

Professor Grunstein, the first non-North American to win the award, will be acknowledged for his significant contribution to professional development in the field of sleep medicine and in researching into the relationships between obesity, metabolic dysfunction and sleep apnoea.

Hopefully his success will prod the rest of us to pay closer attention to the state of our sleep.  But I’m not so sure. Sleep doesn’t seem to rate in dinner party conversation quite as high as other medical disorders.

Up until the turn of this century, it was widely held that five hours or so of sleep a night was adequate to keep one’s mental performance operating smoothly. People simply made do with less sleep. Before long that idea was put to bed, given it grew out of studies where the researchers sent sleepy heads home during the day, where they may or may not have sneaked in a double shot skinny latte or two. Who knows?

An internationally recognised expert in the biological limits of human performance relative to sleep need and circadian biology, David F. Dinges, Professor of Psychology in Psychiatry at the Hospital of the University of Pennsylvania, in 2003 assigned tens of subjects over two weeks to one of three groups: some who slept eight hours (the control group), some six hours and the rest four hours.

He applied a Psychomotor Vigilance Task to the subjects every couple of hours to determine their attention spans. As Maggie Jones in the New York Times Magazine explained, this task involved placing the subjects in front of computer screens for short periods and asked to tap a particular key when they saw a flash of numbers at random intervals: not unlike a visual field test used by ophthalmologists to confirm visual deficits. A delayed response indicated a lapse into sleepiness, commonly called a “micro sleep”.

For good sleepers, the test is like watching paint dry. Boring! But if you’re short on slumber (in both quantity and/or quality), then the test is frustrating. Its purpose is to verify continuous attention that is vital for say, pilots, truck drivers and fire fighters.

The control group (those sleeping eight hours), as hypothesised, hardly had any attention gaps and suffered no memory lapses over the two-week study. Those in the four and six-hour groups had results that skidded steadily with each passing day. Though the four-hour subjects performed far worse, the six-hour group wasn’t that far behind.

Conclusion: for most of us, eight hours of sleep is good and six (or less) hours is bad.

Poor sleep was the anecdotal reason why the lone U.S. air traffic controller at Washington’s Reagan National Airport was enjoying 40 winks, on the job, when two airliners landed in late March, without air traffic assistance. The planes, American Airlines flight 1012 from Miami, a Boeing 737, and United Airlines flight 628T from Chicago, an Airbus A320, with a combined 165 people on board, touched down landed safely at 5:45am.

This episode highlighted a long-known and often ignored hazard: Workers on night shifts, whose sleep is poor, can have trouble staying awake let alone concentrating.