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Richard Horner, professor of medicine and physiology at the University of Toronto and author of the book The Universal Pastime: Sleep and Rest Explained: Sleeplessness affects many branches of medicine.Darren Calabrese/The Globe and Mail

This is the seventh of a nine-part print and online series looking at the science of sleep and the vital role of sleep in maintaining overall health.

When your doctor or, better yet, your mother told you to get more sleep or you'll fall ill, she was actually describing something very complicated on a cellular level.

Everyone knows the draining effects of a sleepless night. And medical researchers have long since moved beyond simple cause-and-effect observations linking chronic sleep problems with poor health. They can now observe what is going on at a more precise level: genetic effects and how cells react to sleeplessness.

There are myriad health risks. At their worst, these can develop beyond general sluggishness to a heightened risk over time of diabetes, obesity or heart disease. It can also lead from mere fogginess to problems with the brain's ability to flush out toxins, eventually leading to memory loss and dementia.

"Part of the issue is that disorders of sleep impact so many organs and tissue functions," said Richard Horner, professor of medicine and physiology at the University of Toronto and author of the book The Universal Pastime: Sleep and Rest Explained.

"It affects the heart, so that's the province of cardiology. It affects breathing, that's the province of respirology. It effects the predisposition to cancer, that's oncology." In fact, sleeplessness affects so many branches of medicine, Dr. Horner said, it has been hard for physicians in any one area to become champions for better sleep.

Yet, sleep research has mushroomed because "it's incredible the amount of people who present to their physicians sleep problems. But the physicians, I would say up until maybe 10 years ago, were ill equipped to understand how to deal with it," Dr. Horner noted.

Complicating the problem is that everyone's natural sleep rhythm, their inner circadian clock, is different, and each body copes physically with sleep deprivation differently.

To illustrate the health effects, Michael Twery, director of the National Center on Sleep Disorders Research at the U.S. National Institutes of Health in Bethesda, Md., likens a sleep deprived body to a car engine: It still runs, but it will start to burn gas inefficiently, lose pep and accumulate carbon deposits. "In the end, a poorly tuned engine will wear out."

And sleep researchers are now observing that gradual wearing out occurs on the cellular and genetic level.

"Now that we can manipulate individual genes, we can measure changes in health that fall short of actually being disease. We can see that when you don't get enough sleep, for instance, you're likely to experience abnormalities in lipid metabolism," Dr. Twery said. (Lipids are basic molecules in cells and include fats.)

"So, we produce more cholesterol, and we produce more of the bad lipids that contribute to cardiovascular disease risk."

Or as another example, stress-related hormones such as cortisol and adrenalin can be released due to sleep deprivation, further contributing to the risk of heart disease. "When adrenalin is elevated all the time, it tends to erode our health, because we weren't designed to be constantly under stress. Not getting enough sleep, being out of rhythm, is a form of stress on our body," Dr. Twery said.

Sleep is also critical for the brain's maintenance, which sounds obvious, but researchers have now found the mechanism in which cerebral spinal fluid flows from the thinking parts of the brain to deeper brain tissues, removing wastes such beta-amyloid which is associated with Alzheimer's disease.

Treatment would seem as obvious as simply sleeping more. But that may not always be possible, such as with sleep apnea, in which breathing is interrupted repeatedly during sleep, preventing a good night's rest and potentially causing a host of health issues.

Doug Bradley, a respirologist at the University of Toronto, noted that sleep apnea is the most easily diagnosed and treatable sleep disorder. But there are many others, and specialists in one disorder are typically not specialists in others.

Another area of special interest is a small portion of the brain's centre: the hypothalamus. Its function includes the metabolism of glucose and lipids, and essentially the rate of metabolism. Yet the difficulty is understanding whether these metabolic functions are affected more by less sleep or by changes in someone's circadian rhythms. In other words, is the problem less sleep or changing sleep?

"The brain's circadian clock may be out of sync with the circadian clocks in every cell. All organs have internal circadian clocks. Every cell has a circadian clock," said sleep specialist Vsevolod Polotsky at Johns Hopkins University in Baltimore, Md.

It is well established in medicine that our internal clocks are largely based around daylight and nightfall. So, working the night shift will throw a body out of whack for a while, but then it might seem to be coping. But is it?

"It doesn't mean that all our organs are adapted. Actually, they're all maladapted. So the question now is which part of sleep deprivation is more important for metabolic and cardiovascular consequences – is it just losing sleep or the misalignment of circadian process?" Dr. Polotsky said. "They are probably both equally important."

Along with this fundamental question, the University of Toronto's Dr. Bradley adds another one. In sleep research, scientists may force a rat to stay awake, then study it. But that's very different than someone deciding to stay awake or to work nights or to read that extra chapter before bed. With the rat, their external conditions are aggressively manipulated. With people, it is a choice. And that raises the question of how psychology and social habits may affect all the medical risks now being studied in labs.

"I think that self-imposed sleep deprivation is a different kettle of fish than externally imposed sleep deprivation," he said.

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