Don146;t lose sleep

8220;Sleep is in the top three,8217;8217; says Dinges. 8220;And I think it8217;s number one. It is a biological imperative and not getting enough has health-related costs.8217;8217;

In the last decade, researchers have begun studying sleep based on today8217;s reality: countries open for business virtually 24/7, and people increasingly unwilling or unable to call it a day. Sleep needs vary slightly, but the vast majority of people, experts agree, need just about eight hours of sleep each night to fully recover from 16 hours of being awake.

Sleep researchers have a name for the way the vast majority of people sleep: volitional chronic sleep deprivation, and it is a lifestyle disorder.

Without enough sleep, the cost in reduced memory, focus, concentration and reaction time is well established. Incidents in the lore of sleep research include the Exxon Valdez oil spill and the Chernobyl nuclear power plant disaster. In each, key decisions were made by people who were sleep-deprived. But it8217;s only in the last half a dozen years that studies have begun to link chronic partial sleep deprivation to serious physical health consequences.

WHAT RESEARCH SAYS

In April, the Institute of Medicine issued a report confirming links between sleep deprivation and an increased risk of hypertension, diabetes, obesity, depression, heart attack and stroke. Some scientists are exploring possible connections between inadequate sleep and a decline in immune function. The Archives of Internal Medicine devoted its Sept. 18 issue to the relationship between sleep and health. An editorial called for assessment of sleep habits as a standard part of all medical checkups. That8217;s because short sleep can hasten the arrival of the inevitable long sleep. The largest study of sleep duration and mortality was published in February 2002 in the Archives of General Psychiatry. The Cancer Prevention Study II of the American Cancer Society followed more than a million participants for six years. The best survival was found among those who slept about seven hours a night, the worst among those who slept less than 4.5 hours. Too much sleep 8212; nine hours or more 8212; also was associated with a higher risk of mortality.

WHY WE NEED SLEEP

Sleep is essential to the workings of every organ. And it seems that the connection between sleep and health starts at the brain8217;s central command post, the hypothalamus. There, sleep or lack of it can work to activate, or inhibit, hormone production. There, too, is where the body gets the signal to go to bed, to wake up and to adjust temperature, blood pressure, digestive secretions and immune activity.

Inadequate sleep works on hormone production in other areas as well. Without enough sleep, the central nervous system becomes more active, inhibiting the pancreas from producing adequate insulin, the hormone the body needs to digest glucose. A groundbreaking study in 1999, led by Eve Van Cauter, a professor of medicine at the University of Chicago, showed that just six days of sleep restricted to four hours pushed 11 healthy young male volunteers into a pre-diabetic state. Those jaw-dropping results expanded the field of sleep research, and convinced scientists that chronic, partial sleep deprivation damaged the body, not just the mind. The young men in the same study also had reduced levels of the stress hormone cortisol, which normally surges just before waking from a good night8217;s sleep, energising people for the day8217;s demands. And these volunteers also showed that, with chronic inadequate sleep, young people might be accelerating the beer-belly, pear-bottom problems typically linked to middle age. They were producing lower levels of growth hormone after less than a week of four hours of sleep. Growth hormone is largely secreted during the night8217;s first round of deep sleep.

As adults age, they naturally spend less time in deep sleep, getting less of the hormone that, in addition to driving childhood growth, plays a role in controlling the body8217;s proportions of fat and muscle.

The University of Chicago study8217;s findings were the first solid evidence that chronic partial sleep deprivation could have physical health consequences. Since then, researchers have begun to look harder and deeper at the links between sleep and illness. A study published in the Dec. 7, 2004, Annals of Internal Medicine found that when 12 healthy, young men were restricted to four hours of sleep for just two nights, normal levels of leptin, a hormone that signals satiety, dropped, while levels of ghrelin, a hormone that prompts appetite, increased. When the men awoke, following the sleep-deprived state, their hunger and appetite increased 8212; especially for calorie-dense, high carbohydrate foods.

8220;Chronic short sleep is the royal road to diabetes and obesity,8217;8217; says Karine Spiegel, a sleep researcher from Brussels and author of the study. Some researchers believe that the links between sleep deprivation and obesity are two interacting epidemics.

The Nurses8217; Health Study, an epidemiologic study begun in 1976 monitoring the health of more than 100,000 nurses, put poundage to sleep loss. In a study reported in the Aug. 16, 2006, issue of the American Journal of Epidemiology, researchers found that after 12 to 16 years, women who slept less than five hours were 5 1/2 pounds heavier than those who slept seven hours nightly.

A good night8217;s sleep also can stave off short-term illness such as colds and flu, as well as hasten the benefits of a flu shot.

8220;Sleep is as important as breathing, drinking and eating,8217;8217; says Dr Meir Kryger, a sleep scientist at the University of Manitoba. 8220;Animals who are deprived of sleep die, but they don8217;t die because their memory is poor. They die a metabolic death: Their fur falls out, they lose weight. Things that happen are over and above just the brain being sleepy. It8217;s critical to health, but it takes longer to notice.8217;8217;