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Coffee thins the deep sleep you get
Caffeine is an alerting drug, in the class of psychoactive stimulants, and the only legal stimulant that is readily given to children. It can keep a person awake at night. For people who fall asleep without trouble, the effect shows up in the depth of the deep sleep instead.
The next morning feels unrefreshed, and since there was no struggle to fall asleep and no memory of waking, caffeine does not look like the cause. The result is that it takes two cups of coffee rather than one, and a vicious cycle builds.
That cycle is probably the reason caffeine is the second most traded commodity on the surface of the planet, after oil.
How does caffeine keep a brain alert?
Adenosine is a chemical by-product of brain activity that builds up across the waking day and promotes sleepiness. It acts on receptors on neurons. Caffeine has a similar shape and occupies those receptors without activating them. Adenosine still accumulates, and its effect is blocked until the caffeine is cleared.
How long does caffeine linger in the body?
The half-life of caffeine in healthy adults averages about five to six hours, though it varies from person to person. A half-life is the time for the level in the blood to fall by half. A quarter of a late-afternoon dose can therefore remain in the body at bedtime. Pregnancy, certain medications, and liver function change the clearance rate.
What did research find about caffeine and deep sleep?
Hans-Peter Landolt and colleagues at the University of Zurich studied caffeine taken in the evening. They recorded brain waves through the night and found that the slow-wave activity of deep sleep was reduced. This held in volunteers who fell asleep without trouble. The result fits with caffeine's blocking of adenosine, which builds the drive for slow-wave sleep.
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