Okay, so my brother in law was a pretty avid cofee drinker, 6 cups a day however he recently cut down to 2 cups due to a nutritionalist telling him that caffiene inhibits the brain from entering deeper cycles of sleep after 3 cups of coffee; however I cannot find any information that it prevents REM cycle sleep;
I know that ingesting caffeine can ultimately enhance circulating levels of ephedine, norephedrine, dopamine etc. and that it is also a stimulant (in that it temporaily reduces the effects of fatigue etc.), but nothing on sleep cycles.
Question is, does caffeine prevent deeper sleep cycles? Or is his 'safe' with his 6 cup a day habit in this regard?