A study in the journal Sleep shows that nearly a quarter of people who sleep fewer than six hours a night have some kind of cardiovascular disease (clogged arteries, an abnormal or weak heartbeat, etc.).

What's more, Harvard Medical School experts say that those who chronically fail to hit the five-hour mark are 15 percent more likely to die at any age from anything.

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On Your Reflexes
After 24 hours without sleep, cognitive motor performance matches that of someone five drinks in, says a study in Nature. Need to game the system? Drink a medium coffee and snooze for 20 minutes. In a famous study out of Loughborough University in England, this trick made exhausted drivers feel alert.

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On Your Stomach
Production of leptin, the hormone that makes you feel full and regulates fat storage, is 15.5 percent lower in those who habitually sleep just five hours, according to University of Wisconsin researchers. Hence the 10 A.M. doughnut craving.

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On Your Waistline
A poor sleeper's BMI is 3.6 percent greater on average, according to Stanford University researchers who found that those who typically get only five hours of shut-eye a night have more body fat. If you snag only four hours, expect to consume an extra 559 calories the following day, per the American Journal of Clinical Nutrition.

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On Your Blood Pressure
A man who regularly dozes fewer than six hours raises his systolic BP to 132 (less than 120 is normal), likely because not snoozing ups cortisol—the stress hormone. To help patients get more sleep, doctors may soon be prescribing Belsomra. Approved by the FDA in August, it adjusts the brain's levels of orexin (a hormone that helps regulate wakefulness) and is expected to have fewer side effects than Ambien.

On Your Pancreas
Men are twice as likely to develop diabetes during their lifetime as a result of sustained sub-six-hour nights, regardless of age or activity level, according to a Yale University Medical School study.

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On Your Brain
Staying up for 19 hours on end three days in a row can damage or kill brain cells, per a new animal study that researchers believe may hold for men too. Scarier still, similar experiments show that without slumber, the brain can't clear out the plaque-forming proteins that cause Alzheimer's and dementia.

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