Alcohol, Caffeine and Sleep: Eyes wide shut

Americans now favor coffee over any other drink, even water, and it’s not just about the taste [1]. Studies suggest that coffee offers vast health benefits, ranging from reduced risks of cardiovascular and neurodegenerative diseases to lower all-cause mortality rates [2]. Interestingly, in regular coffee drinkers, caffeine from coffee activates areas of the brain involved in short-term memory, attention, and focus, whereas caffeine on its own does not [3], which means that there are more perks to your morning coffee ritual beyond merely getting life-giving caffeine into your body (indeed, coffee contains more than 1,000 different molecules!).

However, while your morning coffee might kickstart your day by blocking sleep-promoting adenosine, indulging too late can disrupt your body’s natural circadian rhythms [4]. Caffeine acts as an adenosine receptor antagonist, blocking sleep-promoting signals in the brain; this is how caffeine works to increase alertness and promote wakefulness. One study found that drinking the equivalent of a double espresso (400mg of caffeine) up to six hours before bed shifted participants’ internal clock back by around 40 minutes [4].

This circadian rhythm shift poses challenges for maintaining healthy sleep patterns but suggests coffee’s potential for managing circadian rhythm problems such as jet lag. Furthermore, caffeine consumption has been reported to reduce total sleep time by 45 minutes and sleep efficiency by 7%, with an increase in sleep onset latency of 9 minutes and a decrease in deep sleep, a sleep stage that’s important for repairing and building new bones, muscles, and tissues, regulating glucose metabolism, and supporting immune system function [5]. Caffeine blocks adenosine receptors, which can lead to trouble falling asleep, difficulty falling asleep, and problems staying asleep, especially in caffeine consumers or those with high daily caffeine intake. High doses of caffeine, such as those found in some energy drinks, can have a negative effect on sleep quality and may contribute to chronic insomnia, disruptions in the sleep wake cycle, or other sleep disorders or problems.

Of course, 400mg of caffeine consumption is a fairly high dose—the average cup of coffee contains around 80-100mg—so caffeine’s timing, dose, and impact on sleep require further study. Caffeine content varies widely between products due to many factors such as the type of coffee beans, tea leaves, preparation method, and serving size. Coffee beans and tea leaves are primary natural sources of caffeine, and how much caffeine is present depends on caffeine levels in the specific product. Monitoring daily caffeine intake is important for minimizing sleep disruption, as excessive intake can lead to sleep problems.

Both the timing and amount (caffeine dose) of caffeine administration can significantly affect sleep architecture and perception. Energy drinks often contain high doses of caffeine and other stimulants, which can further disrupt sleep. Caffeine tolerance can develop in regular caffeine consumers, reducing its effectiveness in increasing alertness and potentially leading to higher caffeine doses and greater risk of sleep problems. Older adults are more sensitive to caffeine's sleep-disrupting effects and may need to be especially cautious.

Caffeine peaks in the bloodstream within 30-60 minutes post-consumption and has an average half-life of around 5 hours, meaning caffeine can stay in the system for more than 10 hours. The body takes this amount of time to eliminate half of the caffeine consumed, which is why timing your intake is crucial. Factors such as genetics and medication affect caffeine’s metabolism [6]. For example, oral contraceptives slow down caffeine breakdown, prolonging its presence in the body [7]. Gene variations—specifically, the CYP1A2 and ADORA2A genes—also identify individuals as either fast or slow caffeine metabolizers, which can impact sensitivity to caffeine and sleep quality [8].

Research suggests that caffeine consumption should be stopped at least 8 hours before bedtime to minimize sleep disruption and improve one's ability to fall asleep, and caffeinated pre-workouts should be consumed at least 13.2 hours before bedtime [5]. Those sensitive to caffeine or experiencing sleep issues may want to avoid caffeine at least 10 hours before sleep. For most people, a helpful rule of thumb is to avoid caffeine after noon. Appropriate consumption timing is key to minimizing sleep disruption and maintaining a healthy and consistent sleep schedule. Failing to follow appropriate consumption guidelines can increase the risk of adverse events related to sleep and overall health.

Interestingly, despite coffee’s wakefulness-promoting properties, its efficacy diminishes with consecutive nights of insufficient sleep (5 hours or less), underscoring the importance of quality sleep over caffeine reliance for optimal next-day functioning [9].

After a long day, you may reach for a glass of wine or a nightcap to help you unwind before bed; however, more and more research is highlighting the adverse effects that alcohol can have on sleep. While it’s true that drinking alcohol may help you fall asleep faster, which is certainly part of its appeal, it also disrupts your normal sleep cycle by suppressing REM sleep during the first half of the sleep cycle, which is essential for learning, memory, emotional processing, and waking up feeling refreshed [10, 11]. Alcohol also leads to more sleep disruptions throughout the night and can decrease melatonin production [11, 12, 13]. Even in individuals who felt rested, alcohol still reduced next-day performance and alertness [14].

One study found that alcohol intake was associated with increased sympathetic regulation (our body’s “flight or fight” response) and impacted cardiovascular relaxation during sleep, regardless of gender. These results were observed even in low alcohol intake (less than two drinks per day for men and less than one drink per day for women) [16]. Even men who had fewer than two servings of alcohol per day and women who had fewer than one serving of alcohol per day still experienced a 9.3% decrease in sleep quality. Higher amounts of alcohol consumption were associated with a 24-39.2% decrease in sleep quality. 

The ideal approach is to minimize or avoid alcohol consumption to safeguard your sleep. However, if you do decide to indulge, it's crucial to understand the time your body requires to metabolize alcohol. Alcohol reaches its peak levels in the bloodstream approximately 60-90 minutes after consumption. Its half-life extends to about 4-5 hours, but for the body to fully metabolize alcohol, it necessitates roughly five half-lives, equating to about 25 hours  [ 16]. Thus, despite recommendations to refrain from alcohol consumption 3-4 hours before sleep, this duration still falls short of fully clearing alcohol from your system before bedtime.

Research indicates that even consuming a moderate amount of alcohol six hours before sleep can diminish total sleep time, delay sleep onset, and reduce REM sleep while significantly increasing wakefulness in the latter part of the night  [ 17]. While further research is necessary to ascertain if consuming alcohol more than six hours before bedtime exerts similar detrimental impacts on sleep quality, it's evident that alcohol, particularly when consumed in the evening, adversely affects sleep.

The present study examined the combined effects of caffeine and alcohol on sleep quality. Participants were instructed to keep a sleep diary, recording their sleep patterns, quality, and any obstacles over a six-week period. They also reported whether they had consumed caffeine during the study period, as well as their alcohol intake.

The study found that caffeine and alcohol, when consumed separately, detrimentally affected sleep. Specifically, caffeine shortened sleep duration by 10 minutes for each cup consumed, while alcohol reduced perceived sleep quality by 4% per drink. However, those who reported consuming both caffeine during the day and alcohol at night found that the psychoactive properties of caffeine and the sedative properties of alcohol canceled each other out and, thus, did not impact sleep quality or quantity [18].

Although these findings from the present study are fascinating and merit further investigation, they should not be interpreted as an endorsement for using alcohol in the evening to counteract the stimulating effects of daytime caffeine consumption. Instead, these results highlight the complex cycle of self-medication, especially among individuals experiencing high levels of stress in their personal or professional lives.

It’s also crucial to note that this study relied on self-reported sleep diaries, which may not accurately reflect sleep quality. Comprehensive sleep studies are necessary to fully comprehend the combined impact of caffeine and alcohol on sleep.

While the amount of sleep we get is crucial for mental health, the quality of that sleep is perhaps even more vital in alleviating stress, anxiety, and depression. Practicing good sleep hygiene, such as maintaining a consistent bedtime routine, is essential for improving sleep and achieving a good night's rest. Sleeping in a cool, dark, and quiet environment can also have a strong impact on overall sleep quality. These strategies can also help address common sleep problems that may interfere with restorative sleep. It’s widely recognized that minimizing exposure to blue light and ensuring our sleeping environments are quiet, dark, and cool can enhance sleep quality. However, what additional steps can we take during the day to ensure a restful night’s sleep and consequently, a happier and more stable mood? Here’s some science-backed support to enhance the quality of deep and REM sleep: