The secrets of sleep
It's a mystery, but it clearly makes us smarter and healthier
Sleep deprivation itself, without underlying illness, won't cause mania. "People [with bipolar disorder] can trigger an episode of mania with sleep dep-rivation. And mania is preceded by an episode of insomnia," says Ruth Benca, a professor of psychiatry at the University of Wisconsin. Once mania is diagnosed, adequate sleep becomes one of the most important parts of treatment.
James Swinney, a retired developer on the board of the Depression and Bipolar Support Alliance, knows it. He's been able to regulate his sleep with drugs, including sleeping pills, though he still can't sleep more than six hours a night and often sleeps only in two-hour snatches. "I make sure I get six hours in a 24-hour period," he says.
The six hours Swinney gets is the best he's been able to do, but it isn't enough. Some rare individuals do fine on six hours or fewer, but most people who claim to need less are kidding themselves. They've simply gotten used to chronic drowsiness the way people get used to constant pain. "Everything we know would suggest that the vast, vast majority of people need more than six hours of sleep a night--somewhere between seven and eight," says David Dinges, chief of the Division of Sleep and Chronobiology at the University of Pennsylvania School of Medicine.
During those seven to eight hours, the cardiovascular system gets a break. "Most people, about 85 percent of those with normal or high blood pressure, have a 20 to 30 percent reduction in blood pressure and a 10 to 20 percent reduction in heart rate during sleep," says William White, professor of medicine at the University of Connecticut Health Center. He has monitored blood pressure for 24 hours in about 5,000 people. "It's amazing when you look at people who sleep like a log. Their blood pressure goes down to about 110 over 70."
But what if you're one of those people whose blood pressure, because of some abnormality, doesn't drop at night? Says White: "There's fairly good evidence that you'll develop more damage to your heart, arteries, and kidneys because your blood pressure is elevated 100 percent of the time, instead of 65 percent of the time for those spending one third of their time sleeping," says White.
Morning misery. With a good night's sleep under their belt, people should be expected to wake up with a heart that's raring to go, right? Yet the incidence of heart attacks and strokes peaks between 6 a.m. and 11 a.m. "We don't know why, but maybe the platelets are more sticky," says Virend Somers, a cardiologist at the Mayo Clinic. And sticky platelets are more likely to clot and clog arteries.
Heart attacks generally don't happen to people with no underlying risk factors, such as hypertension or diabetes. But when those are there, waking up during REM sleep may pose dangers. REM is the one stage of sleep that doesn't lower blood pressure. Indeed, during REM sleep, the sympathetic nervous system gets excited, and sleeping blood pressure and heart rate actually rise. Someone getting up during that dream phase might awaken with a pounding heart. And a fast heartbeat and higher blood pressure coupled with waking activity can put added stress on the heart.
advertisement
