For the current study, the researchers scanned the brains of 144 mostly male veterans using magnetic resonance imaging.

They measured sleep quality with the Pittsburgh Sleep Quality Index, a crude, self-rated index that asks broad questions about sleep patterns over the past month. For example, the index asks participants a single question about the time they usually went to bed and another about how long it usually took them to fall asleep.

The researchers found participants who reported poor quality sleep overall had less frontal lobe gray matter than vets who reported sleeping relatively well.

In addition to sleep troubles, a host of psychological problems plagued the study veterans. Half had abused alcohol, 40 percent had had major depressive disorder at some point and 18 percent had PTSD.

Still, the link between sleep troubles and brain volume held even after the researchers took those problems and psychotropic medicine use into account.

Winkelman cautions against inferring a cause-and-effect relationship between sleep and brain volume or generalizing the results of a study on veterans with a range of psychiatric problems to the general population.

But Chao believes the findings could apply to anyone, not just war veterans.