As if folks who are both overweight and sleep-deprived didn’t need more bad news: Those two plights go together.

And some medical experts now think they know why.

A study published in Monday’s Annals of Internal Medicine links insufficient sleep to an inability of fat cells to properly respond to insulin. According to the researchers, when those cells don’t properly handle the insulin, lipids can spill out into the bloodstream and surrounding tissue.

That “metabolic syndrome” is often a precursor to Type 2, or “adult onset” diabetes.

The study focused on seven young, healthy — and yes, thin — people with an average age just under 24. The results showed that even less than a week without enough sleep triggers serious consequences, including significant weight gain.

Matthew Brady, the co-author of the study and an associate professor of medicine at the University of Chicago, warned that getting less than five hours of sleep for four straight nights “is the equivalent of metabolically aging [participants] 10 to 20 years.”

So while many folks had long ago learned the hard way that a lack of sleep diminishes physical energy and mental alertness, it now appears that a lack of sleep also produces a surplus of poundage via a metabolic malfunction of sorts.

As sleep researchers Francesco P. Cappuccio and Michelle A. Miller of the University of Warwick in England wrote in an editorial accompanying the study, it “substantially challenges the traditional views that the primary purpose of sleep is confined to restorative effects on the central nervous system.”

So if you want to lower both your weight and your risk of becoming a diabetic, sleep more and eat less — especially after a prudent bedtime.