Our happy hour fact to amaze your drinking buddies with.

Scientists have a new theory for why people born in the winter months are more susceptible to certain mental illnesses.

Researchers at Vanderbilt University manipulated the amount of light newborn mice received. Some were exposed to a winter cycle of eight hours daylight and 16 hours of darkness, whereas others lived in a summer cycle of 16 hours of sun and eight hours of darkness.

The scientists were then able to determine that when the mice got a littler older, the ones who had been introduced to the world on a summer cycle had a biological clock that wasn't effected by seasonal change. Those mice exposed to a winter-month light cycle experienced issues with their biological clocks.

If this also holds true in humans, it could help explain why people born in winter are at higher risk for suffering from bipolar disorder, schizophrenia and seasonal affective disorder.

However, until that is determined, we can't really recommend running your own summer-month simulations on any wintertime newborns.