Caffeine has been called the most popular drug in the world. All over the world people consume caffeine on a daily basis in coffee, tea, cocoa, chocolate, some soft drinks, and some drugs. Because caffeine is a stimulant, most people use it after waking up in the morning or to remain alert during the day and it’s very effective when used in this way as sleep is readily affected by caffeine.
These is an association between the daily intake of caffeine, sleep problems and daytime sleepiness. So, if you’re struggling to sleep, it’s important to think about how much caffeine you take in during the day.
In excess amounts, caffeine overuse can trigger a fast heart rate, insomnia, anxiety and restlessness, among other side effects.
We know that caffeine stays in the body for several hours. 4-6 hours after you’ve had a cup of coffee for example, your body has only removed half of it. So if you have a cup of tea or coffee within a few hours of bedtime, the caffeine will still be having an effect when you go to bed. The main effects are quite broad, including prolonged sleep latency (it will take longer to fall asleep), shorter total sleep time, increases in the duration of light sleep and shortening of deep sleep time, as well as more frequent awakenings. So caffeine really can and does negatively impact sleep.
The alertness that we feel after consuming caffeine isn’t the same as the alertness we feel after sleep. Caffeine cannot replace sleep. It can only temporarily make us feel more alert by blocking sleep-inducing chemicals in the brain and increasing adrenaline production.
Decaf isn't the same as caffeine free. One study looked at nine different types of decaffeinated coffee and determined that all but one contained caffeine.
Neuroscientist Jeff Iliff discusses brain function during sleep.