The Sleep Equation

QUESTION: Do a few hours of sleep deprivation matter?

ANSWER: It's no secret that lack of sleep seriously impairs both the brain and the body. But for the average American, rest just isn't a top priority.

We will gladly miss an hour of sleep to catch Jon Stewart or Letterman on late-night TV. Maybe we'll make up for it later in the week, or maybe not. Since 1960, the average amount of shut-eye has shrunk from about 8.5 hours to around seven.

Unfortunately, mounting evidence suggests persistent sleep debt—being just shy of optimal rest each morning—can not only weaken immune response and cognitive abilities, but it is also linked to the onset of adult diabetes. Now comes word from scientists that skimping on sleep may make a person fat.

According to a study at Eastern Virginia Medical School, people who sleep just 16 fewer minutes per night than the average person are significantly at risk of being overweight. As inconsequential as those moments sound, it adds up to nearly two hours of lost sleep per week. After controlling for other lifestyle and health factors, researchers calculated that missing two hours of sleep each week is associated with a 10-point increase in body mass index—or the difference between a healthy weight and obesity.