Effect of caffeine and coffee on sleep quality varies, based on individual factors  

Coffee, Caffeine, and Sleep1, a systematic review by Ian Clark2 and Prof. Dr. Hans Peter Landolt3, both of the University of Zürich, examines the results of 58 peer-reviewed epidemiological studies and clinical trials into the effects of caffeine and coffee on sleep.

Overall, the review finds that caffeine typically prolonged sleep latency, reduced total sleep time and sleep efficiency, and worsened perceived sleep quality. Caffeine blocks the adenosine neuromodulator and receptor system, impairing a regulator of sleep-wakefulness. Individuals will respond differently to caffeine based on factors including their age and sensitivity levels.

The authors noted that the studies suggested possible evidence of a dose-response relationship between caffeine and sleep structure: for example, higher bedtime doses of caffeine reduced subjects’ amount of slow wave sleep (also known as ‘deep sleep’). No clear dose-response relationship was found in REM (Rapid Eye Movement) sleep. Outside the laboratory, the authors expect that the general population is consuming enough caffeine to also impact their sleep.

The authors noted that caffeine exposure may be altered as a function of body weight, for example, older adults tend to consume the same amount of caffeine as younger adults but typically weigh less. Older adults may also self-limit the amount of caffeine they consume due to perceived sleep problems. The paper highlights the lack of research conducted into the effects of caffeine in this age group.

Several genes have also been identified that affect an individual’s sensitivity to caffeine. The ADORA2A and ADA genotypes, as well as the DARPP-32 and PRIMA1 genes, have all been connected to caffeine’s impact on a person’s sleep quality. The same amount of caffeine can therefore affect two otherwise similar individuals differently, depending on their genetic make-up.

Clark and Landolt point to a number of limiting factors in existing studies, predominantly the lack of research into the effects of caffeine on women, older adults, and individuals outside North America or Western Europe. Habitual caffeine intake in some study participants could also be a confounding variable when not controlled for.

The authors of Coffee, Caffeine, and Sleep note caffeine’s value as an aid in reducing sleepiness, especially for tasks such as driving at night – and cite the legend of a Yemenite abbot who prescribed coffee to his monks to aid them with their night time prayers. The paper finds no links between coffee consumption and negative health implications, but does note that poor sleep hygiene practices contribute to increased health risk. The review concludes by recommending areas where further research into caffeine and sleep is needed, such as further investigation of how and why an individual’s genetics could predispose them to caffeine-induced sleep changes, and establishing timing and dose-relationships relating to EEG sleep variables.