Regular caffeine consumption affects brain structure

"Data comparison revealed that the participants' depth of sleep was equal, regardless of whether they had taken the caffeine or the placebo capsules. But they saw a significant difference in the gray matter, depending on whether the subject had received caffeine or the placebo. After 10 days of placebo -- i.e. "caffeine abstinence" -- the volume of gray matter was greater than following the same period of time with caffeine capsules. ..

Although caffeine appears to reduce the volume of gray matter, after just 10 days of coffee abstinence it had significantly regenerated in the test subjects."