In the book Why We Sleep, Matthew Walker outlines several negative effects of lack of sleep and the agents that influence sleep. He initiates his discussion with an intense warning of the dangers of not getting enough sleep, which include Alzheimer’s disease, diabetes, heart disease, stroke, weight gain, and mental health disorders. In chapter 2, he explores how caffeine impacts our ability to sleep. I was interested in this topic, since research has shown that caffeine is not directly negative to our health. However, Walker points out the implications that caffeine has on sleep, which suggests a potential indirect link between caffeine and health due to the strong evidence that a lack of sleep is detrimental to overall health.
Caffeine is the most widely used central nervous system stimulant in the world. Caffeine is an adenosine antagonist that binds competitively to the adenosine receptors to suppress sleep pressure, which regulates wake-and sleep cycles. Adenosine builds up in the brain while we are awake, and this accumulation acts as a pressure to determine when we need to sleep. When it reaches a peak, usually around 12-16 hours, the regions of the brain that promote wakefulness will be downregulated and this signals our bodies to go to sleep. When caffeine binds to the adenosine receptors, the brain is no longer signaled to go to sleep but rather it makes you feel alert. (Institute of Medicine (US) Committee on Military Nutrition Research, 2001)
However, there is a paradoxical nature to this alertness. Caffeine has a long half-life of 5-7 hours, making it take a long time before it is completely out of the body (Walker, 2017). Once it is all broken down by liver enzymes, a “caffeine crash” ensues, which produces strong feelings of tiredness, since the buildup of adenosine is finally able to be recognized by the brain. Additionally, the withdrawal symptoms of caffeine include sleepiness, which many people remedy by drinking more caffeine. This creates a cycle, which over time leads to sleep deprivation. It also doesn’t help that the use of caffeine upregulates the adenosine receptors so that more caffeine is required to achieve the same effects. This tolerance promotes increased caffeine intake, which can be even more harmful to sleep. Therefore, it raises the question: is caffeine really worth it?
Research has shown that caffeine does have positive effects on physical abilities and performance such as alertness and reaction time. However, the consequences of caffeine withdrawal, even overnight, are also significant. A study concerned with the withdrawal symptoms found that participants who experienced a caffeine withdrawal overnight performed worse on reaction time tasks and were less alert. This suggests that withdrawal was worse than not drinking a caffeinated beverage. Additionally, they found that losing even just 90 minutes of sleep can lead to reduced daytime objective alertness by one-third (O’Callaghan et al. 2018).
If you are thinking about using a caffeinated beverage to pull and all-nighter and recovering the lost sleep the next day, it may not be the best option. This is because drinking caffeine at night has a greater affect those who choose to stay up at night and try to shift their sleep to the next day than those who follow their normal sleep schedule. This is a result of the circadian rhythm signal for being awake overriding the impact of caffeine and it also has a combined effect with sleep pressure, making it even more difficult to sleep the next day (O’Callaghan et al., 2018).
Caffeine influences the phase of the human circadian rhythm by affecting the production of melatonin and the suprachiasmatic nucleus. Researchers found that drinking caffeine in the evening resulted in a circadian phase delay of 40 minutes, half as much as a phase-shift that was caused by exposure to bright light. The circadian clock was also lengthened via the adenosine receptor and cAMP signaling (Burke et al., 2015). Although this delay of the circadian rhythm is seen as a negative consequence, it has been proposed as a means of resetting one’s circadian clock following time zone travel to reduce jet lag. Due to the long half-life of caffeine and the large variation in people’s abilities to metabolize caffeine, there is the potential for caffeine that is consumed early in the day to interfere with sleep during the night. A study found that drinking caffeine 6 hours before going to bed reduced total sleep time by one hour (Drake, 2013). Therefore, over time this could lead to sleep deprivations and further sleep disordered.
Despite the negative risks associated with caffeine-induced sleep loss, there are actually studies that have shown that moderate coffee consumption decreased mortality risk and risk of developing cardiovascular diseases, type 2 diabetes, Alzheimer’s and Parkinson’s disease, and several types of cancer (Ding, 2015). Several of these diseases are included in the consequences of a lack of sleep that Walker mentions. Since it is evident that caffeine affects sleeping patterns, it is paradoxical that coffee could simultaneously be beneficial to our health but also potentially detrimental if it interferes with sleep.
A potential contributor to coffee being both valuable and causing sleep disruption is the amount of caffeine being consumed. Even if you are getting the same drink and same size every day, the amount of caffeine in coffee is actually highly variable, so you may be getting more or less caffeinated beverage than expected. For example, one day, the coffee had 564.4mg caffeine and another day it had 259.2mg at the same coffee place (McCusker et al. 2003). Since people’s ability to metabolize caffeine is also highly variable, it is difficult to accurately gauge one’s caffeine intake to ensure that it will not interfere with sleep.
Overall, the irony of coffee being able to decrease risk of disease and lack of sleep increasing the risk of the same diseases suggests that if the caffeine can avoid interfering with sleep patterns, it may be beneficial. This data is also an indicator of the complexity of the effects of caffeine and the difficulty studying sleep. There seems to be a fine balance between coffee consumption and interfering with sleep, which can be easily crossed when people build up a tolerance to caffeine and require more consumption to feel the same effects. However, the current data indicates that coffee itself is not only not detrimental to health but that it is actually beneficial, and this information combined with the data on caffeine and its interference with sleep suggests that if this balance of consumption can be achieved, it will be beneficial.
Burke, Tina M, et al. “Effects of Caffeine on the Human Circadian Clock in Vivo and in Vitro.” Science Translational Medicine, U.S. National Library of Medicine, 16 Sept. 2015, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4657156/#:~:text=Caffeine%20can%20acutely%20reduce%20levels,in%20rodent%20models%20(15).
Ding, Ming, et al. “Association of Coffee Consumption With Total and Cause-Specific Mortality in 3 Large Prospective Cohorts.” Circulation, 16 Nov. 2015, http://www.ahajournals.org/doi/full/10.1161/CIRCULATIONAHA.115.017341.
Drake, Christopher, et al. “Caffeine Effects on Sleep Taken 0, 3, or 6 Hours before Going to Bed.” Journal of Clinical Sleep Medicine, 15 Nov. 2013, jcsm.aasm.org/doi/10.5664/jcsm.3170.
Institute of Medicine (US) Committee on Military Nutrition Research. Caffeine for the
Sustainment of Mental Task Performance: Formulations for Military Operations. Washington (DC): National Academies Press (US); 2001. 2, Pharmacology of Caffeine. Available from: https://www.ncbi.nlm.nih.gov/books/NBK223808/
McCusker RR, Goldberger BA, Cone EJ. Caffeine content of specialty coffees. J Anal Toxicol. 2003 Oct;27(7):520-2. doi: 10.1093/jat/27.7.520. PMID: 14607010.
O’Callaghan, Frances, et al. “Effects of Caffeine on Sleep Quality and Daytime Functioning.” Risk Management and Healthcare Policy, Dove Medical Press, 7 Dec. 2018, www.ncbi.nlm.nih.gov/pmc/articles/PMC6292246/.
Walker, Matthew. Why We Sleep. Scribner, 2017.