Sleep problems are common for many following Western lifestyles. Studies have investigated the reasons contributing to this widespread insomnia and a number of possible theories have been suggested. However, taken as a whole the scientific evidence suggests that insomnia is multifactorial, but centres on the consumption of a poor diet, combination with high amounts of environmental stress. A number of lifestyle choices can also influence sleep patterns, with one of the most well recognised being caffeine intake. Caffeine is a stimulant, and antagonist to the adenosine receptor. The adenosine receptor is now understood to play a role in sleep and relaxation, and by antagonising the receptor, caffeine can prevent drowsiness and sleep. High caffeine intakes, particularly in those not habituated to caffeine or those who are sensitive, can therefore be a cause of insomnia. A number of studies have investigated the effects of caffeine on sleep and brain activity associated with sleep.
For example in one study1, researchers assessed the effects of 100 mg of caffeine administered at bedtime or a placebo treatment in respect to electroencephalogram (EEG) changes and sleep patterns. The results of the study showed that caffeine increased sleep latency (the duration between waking and falling back to sleep) significantly as expected. The caffeine levels in the saliva of the subjects fell from 7.5 μmol/L to 3.5 μmol/L during the first hour of sleep, as metabolism of caffeine proceeded. In addition, the EEG showed that caffeine reduced the efficiency of stage 4 and non-rapid eye movement sleep. but these values returned to baseline the night following caffeine administration. Caffeine reduced the power density of the lowest delta band of sleep, the band of sleep associated with the deepest sleep. Therefore caffeine administered before bed disrupts sleep patterns. However, tea contains L-theanine which may induce relaxation, and so the effects of caffeine containing beverages are more complex.
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