Sleep is good for you. So what happens when age-old culprits like insomnia or sleep apnea—or newer ones like a jam-packed schedule—cause you to lose sleep? That’s right, they may affect your health—particularly your heart.

August 16, 2012

Far from being a time-wasting, 8-hour sentence in a useless void, the research is pretty clear on this point: sleep is crucial for good health. It helps memory and mood, keeps you trim, strengthens your immune system, fights inflammation, and keeps your heart and blood vessels in tip-top shape.

“When you’re sleeping you’re regulating hormone levels, you’re regulating insulin levels, your blood pressure is being kept under control, there are a lot of things going on, and if you’re not getting enough sleep you’re throwing these things out of whack,” says Shelby Freedman Harris, PsyD, director of behavioral sleep medicine at Montefiore Medical Centers Sleep-Wake Disorders Center in New York City.

While you’re snoozing, the body repairs damaged tissue, produces crucial hormones, and strengthens memories—a process called consolidation, which helps you perform a new skill better after sleeping than you would if you spent an equivalent amount of time awake. (Take that, all-nighters!)

“It’s a way for the body to integrate everything that happened over the past waking day and to kind of prepare for the next day,” says Virend K. Somers, MD, a professor of medicine and cardiovascular diseases at the Mayo Clinic in Rochester, Minn., who studies sleep and heart health.

Hopefully, you’re convinced that sleep is good for you. So what happens when age-old culprits like insomnia or sleep apnea—or newer ones like a jam-packed schedule—cause you to chronically lose sleep? That’s right, they may affect your health—particularly your heart. (In general, short stretches of sleep deprivation—when taking care of a new baby, for example—can be challenging, but aren’t thought to have a long-term effect on health).

Why your heart needs a good night’s sleep

Short sleepers, typically defined as people who get less than six hours of sleep a night, as well as people who don’t spend enough time in the deepest stages of sleep, are at higher risk of heart attacks and strokes than those who get at least seven hours.

A 2011 study in male Japanese factory workers found those who slept less than six hours a night had a five-fold increased heart attack risk over a 14-year span compared with those who logged between 7 and 8 hours a night. Another published in 2011 found that healthy men 65 and older with normal blood pressure were nearly twice as likely to develop hypertension during the study if they spent less time in the deepest sleep stage (known as slow-wave sleep) compared with those who spent the most time deeply asleep.

There’s also some limited evidence that short-term sleep deprivation may be harmful to those with heart problems. In 2012, Swedish researchers reported that hospital admissions for heart attacks increased by about 4% in the week after the spring transition to daylight saving time compared to other weeks. This is when we “spring forward” and set our clocks an hour ahead—meaning many of us lose an hour of sleep.

Its not clear why sleep may affect the heart, or if there is some unidentified factor that affects your cardiovascular system and ability to sleep. But one nighttime problem is a known heart hazard—sleep apnea. People who have sleep apnea tend to snore and have upper airway collapse during sleep. This causes them to snort and gasp for breath, without really waking up enough to be aware of it.

“It’s as if somebody’s choking you, so your heart rate goes up, your blood pressure goes up, and instead of having a daily cycle in which everything slows down at night, instead everything is higher during the night,” says Charles Czeisler, MD, the Baldino Professor of Sleep Medicine at Harvard Medical School in Boston. “Over time, even your daytime blood pressure is higher.” In fact, he adds, many experts think sleep apnea may account for one-third of all cases of high blood pressure among adults.

If you’re not feeling rested during the day and your bed partner says you snore, you should ask your doctor about sleep apnea. “Theres enough evidence out there suggesting that sleep apnea is bad that people need to take it seriously,” Dr. Somers says.

People with less severe sleep apnea may be able to get their symptoms under control by just adopting strategies that prevent them from sleeping on their back, for example sewing a tennis ball into the front pocket of a T-shirt and wearing it backwards, Harris says. There are even shirts that you can buy with built in padding to prevent back sleeping.

For more severe cases, a device can help prevent the lower jaw from falling backwards into the airway, Dr. Somers says, or a face mask that delivers pressurized air into the nose (called continuous positive airway pressure, or CPAP) can keep the airway open at night.

Is lack of sleep making you fat?

Recent research also suggests that a lack of sleep could be contributing to problems like diabetes and weight gain, both serious health hazards. Some studies have linked shorter sleep to a greater likelihood of obesity, but whether or not sleeping less is a cause or effect of obesity remains unclear.

What we do know is that sleep deprivation reduces sensitivity to insulin, the key blood-sugar-regulating hormone, while making it harder metabolize blood sugar properly. Short sleep also boosts levels of hormones that make us hungry, while reducing secretion of the hormones that help us feel full. So it makes sense that being starved for sleep could lead to weight gain—even if only for the fact that being awake longer gives us more time to eat.

When people are sleep deprived and eat a cookie, their blood sugar goes higher and they’re more resistant to the effect of insulin than if they ate the same cookie after a good nights sleep, says Dr. Czeisler. “If youre on a diet to lose weight and you’re sleeping five to six hours a night, 75% of the weight you lose will be lean body mass.”

That means just 25% of the weight you’re losing is fat, he added; when people sleep enough, fat accounts for 50% of weight lost.

“A lot of people who don’t get enough sleep often say they have trouble losing weight, or they have this slow weight gain,” notes Montefiores Harris. Often, she adds, people who start getting treatment for sleep apnea find that once theyre sleeping better, its easier for them to lose weight—and losing weight may help lessen sleep apnea

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