Not getting quite enough shut-eye? Even if you don’t feel tired, shorting yourself on sleep can affect your ability to function.

In a tightly controlled study at Brigham and Women’s Hospital in Boston, researchers allowed participants to snooze for just five-and-a-half hours each night. The longer they maintained that sleep schedule, researchers found, the worse they did on visual performance tests — even when the participants themselves reported that they didn’t feel that tired.

The results come as researchers are learning an unprecedented amount about the importance of a good night’s sleep, which may help prevent everything from high blood pressure and diabetes to osteoporosis.

New findings suggest that sleep deprivation also has consequences for the immune system, which reacts to sleep loss the same way it reacts to stress. But the findings that link poor sleep habits to being overweight or obese might be the most intriguing of all.

In the journal Current Biology, German researchers revealed how weight gain can be caused by a disconnect between people’s normal work hours and the hours their bodies would prefer to sleep.

The published study used the term “social jet lag” to refer to the experience of people who sleep on one schedule during the work week and adjust their sleep patterns to get an extra hour or two of rest on the weekends.

The researchers found that for every hour of this “social jet lag,” a person’s risk of becoming overweight or obese increased by about one-third.

Study authors say the best way for people to combat social jet lag is to embrace the body’s preferred natural sleep pattern, which probably calls for sleep between 1 a.m. and 9 a.m.

But that kind of sweeping shift in society is not on the horizon. So don’t call your boss and say you’ll be in at 10 just yet.