There is probably no time of year when America's sleep debt is
greater than it is right now. Starting with Thanksgiving week, holiday
preparations and parties, gift shopping and packaging, family visits
and extra hours of work to make up for days off prompt millions of
Americans to cheat on their sleep even more than usual. Many are used
to being tired and think, optimistically, that they'll catch up with
lost sleep after the New Year.
This is the first of two columns on sleep debt. Next week: the value of naps.
In a study inspired and partly financed by the MacArthur Foundation, Dr. Katrine Spiegal, Dr. Eve Van Cauter and Rachel Leproult found that even in young, healthy people, as little as a weeklong sleep debt of three or four hours a night has adverse effects on the body's ability to process carbohydrates, manage stress, maintain a proper balance of hormones and fight off infections.
Sleep Lost, Never Regained
Most previous studies looked only at short-term sleep deprivation -- keeping people awake for 24 or 48 hours -- and explored only the effects on mental performance, alertness and mood, which do indeed suffer from a lack of sleep. In the new study, Dr. Van Cauter and colleagues examined the physiological effects of sleeping only four hours a night for six straight nights, a not uncommon practice, especially at this time of year. As one of millions trying each day to cram 36 hours' worth of activity into 24, I listened carefully to what Dr. Van Cauter had to say, and I suggest you do too.
"With prolonged sleep deprivation, we found effects much more relevant to health than result from the loss of one or two nights' sleep," Dr. Van Cauter said in an interview. "We found that an accumulated sleep debt is potentially as detrimental to health as poor nutrition or a sedentary lifestyle. It may be as bad as smoking. People are sleeping less and less and becoming more and more tired. They may be very careful about exercise, good nutrition and vitamins, but they're sleeping only five hours a night."
When Sleepless Nights Spell Trouble
James Maas, author of "Power Sleep" (HarperCollins, 1999), says an answer of "true" to two or more of the following statements may be signs of a sleep problem.
I need an alarm clock in order to wake up at the appropriate time.
It's a struggle for me to get out of bed in the morning.
Weekday mornings I hit the snooze button several times to get more sleep.
I feel tired, irritable and stressed out during the week.
I have trouble concentrating and remembering.
I feel slow with critical thinking, problem-solving and being creative.
I often fall asleep watching television.
I often fall asleep after heavy meals or after a low dose of alcohol.
I often fall asleep while relaxing after dinner.
I often fall asleep within five minutes of getting into bed.
I often feel drowsy while driving.
I often sleep extra hours on weekend mornings.
I often need a nap to get through the day.
I have dark circles around my eyes.
Previous studies have indicated that the average adult needs eight to nine hours of sleep a night, but the typical American gets only seven and many get considerably less, without ever catching up. While it is true that individual sleep needs vary -- there are natural "short sleepers" and "long sleepers" who fall well outside the average -- it is also true that many short sleepers push themselves considerably beyond what is natural, staying up until midnight doing chores or watching television, then rising to an alarm at 4:30 or 5 a.m. These are the people who fall asleep on commuter trains and buses, at plays and concerts and, sometimes, behind the wheel. Some even doze off at business meetings or at the computer.
A Physiological Toll
Dr. Van Cauter and colleagues found that sleep deprivation caused "striking alterations in metabolic and endocrine function" that mimicked some of the hallmarks of aging. They conducted a very thorough study of 11 healthy men aged 18 to 27 who spent 16 consecutive nights in a clinical laboratory where the researchers tightly controlled the amount of time they spent in bed. After three 8-hour nights, they were restricted to six consecutive 4-hour nights, followed by seven 12-hour nights. None were allowed to sleep during the day.
Repeated blood and saliva samples enabled the researchers to gauge the metabolic and hormonal effects of the shortened nights. Striking deficits occurred in the participants' abilities to process glucose. This results in a rise in blood glucose, a condition that prompts the body to spew out more and more insulin, which ultimately leads to insulin resistance, the hallmark of adult-onset diabetes. Excess insulin also promotes the storage of body fat, thus increasing the risk of obesity and high blood pressure.
The brain can use glucose for energy without the aid of insulin, but it too was less effective at processing glucose during the period of sleep deprivation. This would diminish the functioning of some areas of the brain and may explain why critical thinking, memory and mental sharpness are impaired by inadequate sleep.
The researchers also found that blood levels of cortisol, a measure of stress, were higher in the afternoon and evening in the sleep-deprived subjects. Such rises in cortisol are typical of the aging process, and are associated with adverse health effects, including insulin resistance and memory impairment.
Thyroid hormone levels were also distorted by sleep loss, but the researchers declined to speculate on the consequences of this abnormality. They also found evidence of immunological impairment during the period of shortened nights. The participants were less responsive to flu vaccine.
The Chicago team is now conducting further studies of sleep deprivation in women and older adults. Dr. Van Cauter says she expects the consequences in older people to be even worse, since the time spent in deep sleep, the most restful kind, normally declines drastically with age -- from 100 minutes a night in people aged 20 to 25 to less than 20 minutes by middle age. When young people become sleep-deprived, they can make up for the loss of deep sleep, but older people may not be able to compensate adequately, she said.
What You Can Do
"People have to become more reasonable about sleep if they want to stay healthy," Dr. Van Cauter said. She suggests that those who are cheating on their sleep should "go to bed one or two hours earlier" rather than turn off the morning alarm and arrive late for work. High school students are among the most sleep-deprived. "They go to sleep at midnight and get up at 6 a.m. and arrive at school like zombies," Dr. Van Cauter said.
"Our society seems to place a moral value on sleeping as little as possible," she noted. "In Europe, people are less impressed by short sleepers. Here we're almost embarrassed to say that we are going to bed early. Saying 'I'm tired and I'm going to sleep' is viewed as being lazy."
Studies by Dr. David Dinges, sleep researcher at the Institute of Pennsylvania Hospital and the University of Pennsylvania in Philadelphia, found that after two weeks of chronic sleep loss, people may say they have adapted to less sleep and are not sleepy.
But he showed that even those who think they have adapted performed poorly on tasks that are impaired by fatigue.
"Clearly, there's a disconnect between objective and subjective sleepiness," Dr. Van Cauter said. "In our study, no one adapted."
And in case you think you get more done by sleeping less, a study of how two adults used the extra time when their sleep was reduced to five and a half hours a night revealed that they got no more done: everything they did took longer.
Copyright 1999 The New York Times Company
Tuesday, December 28, 1999