A study conducted by scientists at Washington University School of Medicine in St. Louis found that smoking shrinks the brain.

The researchers found that because people's brains naturally lose volume as they age, smoking essentially causes the brain to age prematurely

“It is bad, and it sounds bad,” Bierut remarked. “An increase in age is correlated with a decrease in brain volume

It is inherited that smoking habits and brain size are related. About half of a person’s risk of smoking comes from their genetics.