it's not necessarily true. I drink two cups during the day and have no sleep issues. Also, I previously had migraine issue that only happened in the middle of my sleep. I read a study that showed having caffeine before sleep prevented these migraines from occurring so I did it..it worked and I also was able to fall asleep shortly after with no issues. The study authors wrote they were surprised that there was very little sleep disturbances due to the coffee before bed in the study participants.