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Never underestimate the value of a good night's sleep. Not only does a lack of shut-eye leave you irritable, it has been linked to diabetes and weight gain, though no one understood why.

To investigate, Matthew Brady at the University of Chicago and his colleagues tested fat cells taken from the bellies of seven adults after four nights of sleeping up to 8 and a half hours, and then again after four nights on a measly 4 and a half hours.

The team found that after sleep deprivation fat cells from the same person were on average 30 per cent less responsive to insulin  - a hormone that makes muscle, liver and fat cells take up glucose after a meal.

High blood glucose levels are linked to diabetes. Fat cells also normally release the appetite-regulating hormone leptin. Brady suggests that if sleep-deprived cells are generally malfunctioning, this mechanism may also be disrupted, affecting weight gain.

"We were surprised at how robust the response was," says Brady. "Four nights of sleep curtailment represents a real-world situation, such as sitting for final exams or having a newborn in the house."

Journal reference: Annals of Internal Medicine, DOI: 10.7326/0003-4819-157-8-201210160-00005