Studies stress benefits of sleep

In one study, disruptive sleep led to lowered sensitivity to insulin.

SCRIPPS HOWARD NEWS SERVICE

Even with sleeping in on New Year’s Day, many of us are starting 2008 feeling groggy. And that could well undermine more than a few good intentions about losing a few pounds.

New studies out over the holidays show that sleep deprivation affects weight gain and diabetes risk, underscoring the complex connections between our brains and digestive systems.

One report, published online by the Proceedings of the National Academy of Science, particularly focused on how the suppression of deep sleep hurts the ability to regulate blood-sugar levels even in young adults.

A second, published in the journal Sleep, looked at children at four stages from birth to 7 years, and found that those who slept less than nine hours a night were more likely to be overweight or obese at age 7 than those who slept for more than nine hours. They were also more likely to have higher levels of body fat.

“Sleep is important for health and well-being throughout life,” said Ed Mitchell, a professor at the University of Auckland, who led the study of nearly 600 New Zealand children.

Lots of studies have shown that reduced amounts of sleep can impair metabolism of sugar in the blood and regulation of appetite, resulting in an increased risk of obesity and diabetes, along with emotional and cognitive difficulties and damage to the immune system.

But the deep-sleep study by researchers at the University of Chicago Medical Center showed that even as little as three consecutive nights of disrupted slow-wave sleep was enough to make young adults — ages 20 to 31 — less sensitive to insulin. The decrease in insulin sensitivity was equivalent to having gained 20 to 30 pounds.

“These findings demonstrate a clear role for slow-wave sleep in maintaining normal glucose control,” said Dr. Esra Tasali, an assistant professor of medicine who led the study. It involved nine volunteers — five men and four women — who had their deep sleep subtly disturbed by sounds from speakers mounted by their beds.

The sounds were loud enough to disturb deep sleep, but not loud enough to wake the subjects completely. This cut the amount of deep sleep by about 90 percent, but did not alter total sleep time.

“Since reduced amounts of deep sleep are typical of aging and of common obesity-related sleep disorders, such as obstructive sleep apnea, these results suggest that strategies to improve sleep quality, as well as quantity, may help to prevent or delay the onset of type 2 diabetes,” said Eve Van Cauter, a professor of medicine and senior author of the study.

Young adults typically spend 80 to 100 minutes a night in slow-wave sleep — the final period of sleep cycles that normally last several hours. People over age 60 generally have less than 20 minutes of deep sleep a night.

“For this experiment, we gave people in their 20s the sleep of those in their 60s,” Tasali said.

Thus, the researchers speculate that it may be more important to improve the quality of sleep in those of advancing age, even if they sleep less overall.

Still other research, by scientists at the Wake Forest University School of Medicine, published this week in the Journal of Neuroscience, shows that at least the effects of sleep deprivation on cognitive performance might be reversed with an extra dose of a particular brain protein.

Although the study involved monkeys, “the findings are significant because of the potential applications [for humans],” said Samuel Deadwyler, a professor of physiology and pharmacology at Wake Forest.

“This could benefit patients suffering from narcolepsy and other serious sleep disorders. But it also has applicability to shift workers, the military and many other occupations where sleep is often limited, yet cognitive demand remains high.”

The monkeys in the experiment were pushed through an all-nighter with a combination of videos, music, food and interaction with lab techs until their normal time for performance of trained tasks the following day.

Their performance was well short of normal.

But when sleep-deprived monkeys were given a dose of a naturally occurring brain protein called orexin-A, either intravenously or in a nose spray, just before testing, their cognitive skills returned to normal levels.

But the researchers also found that giving a dose of the substance to monkeys that were not sleep-deprived had no effect on their performance with the tests.