Investigating the effects of psychoactive substances on subsequent sleep

Sleep is essential for health and wellbeing. However, it is estimated that up to 40% of the population fail to attain the recommended seven to nine hours of sleep per night. A key contributor to these high rates of sleep insufficiency is the consumption of psychoactive substances. Two widely accessible psychoactive substances are alcohol and caffeine. Alcohol, the most commonly consumed hypnotic, is consumed by approximately 40% of the population, while caffeine, the most commonly consumed stimulant, is consumed by approximately 80% of the population. This thesis aims to investigate the impact of these common psychoactive substances on subsequent sleep. By focusing on the influence of the dose and timing of intake, the program of research aims to provide evidence-based guidance to minimise the negative effect of alcohol and caffeine on subsequent sleep. Additionally, the thesis investigates the efficacy of theacrine as an alternative substance to caffeine to mitigate the cycle of insufficient sleep and subsequent caffeine reliance.

Chapter 4 (Study 1) is a systematic review and meta-analysis with the aim of establishing the level of evidence for and to quantify the effect of alcohol on subsequent sleep. Additionally, Chapter 4 aimed to quantify the effect of the dose and timing of alcohol intake using meta-regression analysis. The analysis revealed that alcohol consumption negatively impacted rapid eye movement sleep (REM) when consumed at a low dose (≤0.50 g∙kg-1), with greater REM sleep disruption occurring with larger doses of alcohol. Furthermore, both sleep onset latency and latency to non-rapid eye movement (NREM) stage three (N3) sleep were reduced with consumption of a high dose of alcohol (≥0.75 g∙kg-1). Participants typically perceived a shorter sleep onset latency but were unaware of the subsequent objectively measured sleep disruption. The use of alcohol as a sleep aid poses a serious risk to consumers sleep, with progressively larger doses resulting in greater REM sleep disruption.

Chapter 5 (Study 2) is a systematic review and meta-analysis with the aim to establish the level of evidence for and to quantify the effect of caffeine on subsequent sleep. Additionally, Chapter 5 aimed to quantify the effect of the dose and timing of caffeine intake using meta-regression analysis. The analysis revealed that caffeine consumption negatively impacted total sleep time, sleep efficiency, sleep onset latency, and wake after sleep onset. Furthermore, caffeine consumption increased the proportion of NREM stage one (N1) sleep at the expense of the deeper stage of N3 sleep. Participants were unable to perceive the increase in sleep fragmentation that occurred with caffeine consumption. Cut off times for the consumption of common caffeine products were identified to provide guidelines to minimise significant reductions in total sleep time: a cup of tea (47 mg per 250 mL) could be consumed up to bedtime, a cup of coffee (107 mg per 250 mL) should be avoided within 8.8 hours of bedtime, and a standard serve of pre-workout (217.5 mg) should be avoided within 13.2 hours of bedtime.

Chapter 6 (Study 3) was an experimental investigation of various caffeine dose and timing combinations on subsequent sleep. The conditions were designed to replicate a low (100 mg) and high (400 mg) dose of caffeine consumed in the morning (12 hours prior to bedtime), afternoon (eight hours prior to bedtime), and evening (four hours prior to bedtime). Results showed that a 100 mg dose of caffeine could be consumed up to four hours prior to bedtime without a significant effect on subsequent sleep. However, the 400 mg dose of caffeine negatively impacted subsequent sleep when consumed 12 hours prior to bedtime, with greater effect when consumption occurred closer to bedtime. Participants could only perceive disruption to sleep when 400 mg was consumed four hours prior to bedtime, highlighting the inability of consumers to perceive sleep disruption following daytime consumption of a high dose of caffeine.

Chapter 7 (Study 4) replicated the experimental design of Chapter 6 to investigate the effect of varying theacrine dose and timing combinations on cognitive performance and subsequent sleep. Results showed that regardless of the dose and timing of intake, theacrine had no significant effect on subsequent sleep. However, significant improvements in cognitive performance were observed when assessed 15-minutes after waking the following morning. The findings suggest theacrine holds potential as an alternative to caffeine to improve cognitive function and further scientific investigation is warranted.

The program of research within this thesis demonstrates the negative effect of both alcohol and caffeine consumption on subsequent sleep. Importantly, the findings identify the disconnect between perceived and actual effects of alcohol and caffeine on subsequent sleep. This disconnect may explain why consumers willingly engage in patterns of consumption that leave them susceptible to insufficient sleep and subsequent reliance on either or both substances. By employing methods to quantify the influence of dose and timing of intake, the thesis provides consumers with actionable and evidence-based guidance to mitigate the sleep disruption caused by the consumption of alcohol and caffeine. Finally, the thesis presents evidence to support further scientific investigations regarding the potential use of theacrine as an alternative to caffeine.

This work © 2024, Carissa Gardiner