Building on research linking inadequate sleep to obesity and diabetes, scientists in a new study say they have figured out for the first time how that connection might work at the cellular level.

In a small study in the Annals of Internal Medicine, researchers found that not getting enough sleep hurts the ability of fat cells to respond to insulin efficiently. This state of insulin resistance or "metabolic syndrome" is often a precursor to Type 2, or adult-onset, diabetes. Participants in the study who on four nights were in bed for 4½ hours had fat cells that were 30% less responsive to insulin than the cells were after four nights of 8½ hours in bed.

"If you're cramming for finals or have a newborn in the house," getting 4½ hours of sleep isn't unusual," said Matthew Brady, an associate professor of medicine at the University of Chicago and a co-author of the study. Yet after just four nights, "it is the equivalent of metabolically aging [participants] 10 to 20 years." The study involved seven thin, young, healthy people with an average age just under 24.

Most adults need between seven and nine hours of sleep a night.

The study adds fuel to the larger scientific debate over the purpose of sleep. Sleep deprivation has been shown to reduce attention, slow reaction times and impair learning. This study shows it can be harmful to the metabolism, as well.

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