Fat cells need sleep, according to a new study.

In study participants who were deprived of sleep, fat cells showed a decreased ability to respond to insulin, a hormone that regulates blood sugar levels, according to the study.

"Just as when you're sleep-deprived, you're groggy – it turns out that sleep deprivation also makes your fat cells metabolically groggy," said study author Matthew Brady, an associate professor of medicine at the University of Chicago.

The study included only six men and one woman, but all participants showed decreased insulin sensitivity after sleeping 4.5 hours each night for four consecutive nights, compared with when they slept eight hours nightly, for four consecutive nights, the researchers said. The participants were all lean and healthy, and their average age was 24.

"Just four nights of four and a half hours of sleep in bed was enough to metabolically age them by 10 to 20 years," Brady said. "If this sleep deprivation persisted, then we would predict they would be at a greater risk for developing metabolic diseases such as obesity and Type 2 diabetes."

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The researchers conducted blood tests called intravenous glucose tolerance tests, which measure total-body insulin sensitivity, and removed fat cells from just underneath the skin of the participants' abdomens, and measured the cells' sensitivity to insulin.

Total body insulin responses decreased 16 percent on average when the participants were sleep-deprived, compared with when they slept eight hours. In particular, a protein called Akt1 became 30 percent less active in the fat cells of sleep-deprived participants.

The researchers also found that when study participants were sleep-deprived, the amount of REM sleep decreased by half. REM sleep is associated with healthful rest.

However, other experts noted the sleep deprivation used in the study was not similar to what's typically seen in real life.

"When we talk about sleep-deprived people, it's usually more like people who sleep between five and six hours per night, over long periods of time," said Lilian de Jonge, a staff scientist at the National Institutes of Health. "It's possible that over a long period of time, people can actually adjust their metabolism to sleep deprivation — we don't know," she said.

Moreover, sleep experiments conducted in research labs don't always mimic real life because the quality of sleep, not only the amount, matters, de Jonge said.

"You never sleep as good in the hospital bed than you sleep in your own bed, especially not if you're hooked up to all kinds of stuff, so it is possible it is sleep quality and not sleep time (that caused the results)," de Jonge said.

Next, the researchers said they will examine sleep interventions to help obese patients not only improve their sleep, but potentially their weight.

"If you improve their sleep quality and sleep duration, you might be able to take someone who has a metabolic impairment and help improve them just through a sleep intervention," Brady said.

The study appears in the Oct. 16 edition of the Annals of Internal Medicine.