Caffeine, sleep and quality of life

Caffeine is regarded as a mild stimulant acting on the central nervous system that is responsible for a significant portion of the behavioural and physiological effects of coffee and tea. Motives why people take caffeine are reflected in consumption patterns. Early in the morning caffeine might help to wake up, whereas during the day it is an aid to stay awake or counteract fatigue. The intake of caffeine shortly before sleep might affect sleep characteristics, especially if high doses of caffeine are used. Moreover, these disturbances of sleep might result in tiredness in the morning. Caffeine is frequently used as a countermeasure for fatigue and sleepiness. During sub-optimal circumstances such as working night shifts and sleep deprivation it maintains performance and wakefulness at satisfying levels. These effects of caffeine depend largely on its antagonistic actions on the A2A adenosine receptor. Simple task performance seems in particular sensitive to caffeine. Part of the caffeine effects might be due to withdrawal reversal, although caffeine is stimulating in non-withdrawn subjects, as well. In addition, in habitual users, there is no complete tolerance to the effects of caffeine.