Caffeine consumption and its effects on the human body

Caffeine is one of the most widely consumed psychoactive substances in the world, with billions of people regularly consuming it through coffee, tea, energy drinks, and other sources. 80% of people worldwide ingest caffeine on a regular basis, making it the most popular stimulant. Its popularity stems partly from its well-known effects on alertness and energy levels. 

Image 1: Caffeine found in various beverages and foods

Caffeine Mechanism of Action

3 methyl groups are added to the parent chemical xanthine to create caffeine (1,3,7-trimethylxanthine). Following ingestion, caffeine is rapidly absorbed from the gastrointestinal system, reaching 99% absorption in 45 minutes. Adenosine, a neuromodulator whose production depends on the relative rates of ATP synthesis and breakdown, shares structural similarities with caffeine.  

Adenosine receptors are extensively dispersed across cortical areas, and caffeine is an effective medication that swiftly crosses the blood-brain barrier due to its hydrophobic qualities to inhibit them. Caffeine significantly boosts firing rates in areas that mediate mood and sleep, including the locus coeruleus and the dorsal and medial raphe nuclei, even at modest dosages. Increases in sustained attention, quicker response times, and subjective feelings of alertness are all likely caused by this increased cortical activity.

Caffeine Dosage

It is well known that in a dose-dependent fashion, caffeine raises alertness. Modest amounts can enhance hedonic tone and provide relief, whereas excessive doses exacerbate tension and anxiety, jitteriness, and uneasiness symptoms. 

Image 2: Yerkes-Dodson Law

The Yerkes-Dodson law states that there is an empirical correlation between arousal and performance, with low arousal being linked to subpar performance and higher physiological or mental arousal being linked to enhanced performance—but only to a certain extent. Performance declines when arousal levels get too high. Therefore, the effects seen will depend on the subject's pre-dose arousal level prior to ingesting caffeine.  Caffeine promotes a favourable arousal level in this situation, which means that giving a big dosage to someone who is really tired is likely to increase performance i.e. caffeine moves the subject’s arousal into the middle range of the curve. 

On the other hand, administering the same dosage to a person who is already well-rested and highly aroused may actually impair performance rather than enhance it since caffeine causes an overarousal state, which impairs cognition in accordance with the curve. As they adjust their caffeine intake till they attain their self-selected ideal level of arousal and cognitive function, there is evidence that people utilise caffeine to obtain a self-perceived, peak state of arousal under typical daily conditions.

Effect on Memory

There are 2 types of human memory: short-term memory, often known as working memory, and long-term memory. Information is temporarily stored in working memory so that further processing (like recognition) can take place. When directing and carrying out intricate cognitive activities, working memory offers the capacity to preserve and modify information. Large volumes of data are kept in long-term memory for extended periods of time—up to a lifetime. Generally speaking, all data kept in the human brain for more than two minutes is regarded as long-term memory.

Short-term Memory

Researchers discovered that whereas greater doses of caffeine impair working memory function, lower levels improve it. According to other research, coffee improves performance on low-load memory activities but degrades it on high-load ones. This could be the result of elevated arousal brought on by demanding tasks, which, when combined with coffee, may cause over-arousal and impair memory function. The individuals' memory performance suffered as a result of the extra arousal brought on by novelty pushing them over the top of the Yerkes-Dodson curve.

While younger participants may be more vulnerable to coffee-induced overactivation because they are already functioning very near to an ideal arousal level under normal circumstances, older adults may have age-related arousal declines that are mitigated by greater caffeine doses.

Long-term Memory

Caffeine's effects on long-term memory has not been the subject of much research to this date.

Effect on Learning

The variable being examined is one of several factors that go into learning and memory tasks, along with a number of other factors including mood, response time, and the degree of attentiveness and attention. Caffeine has been shown time and time again to improve mood, boost alertness and concentration, and shorten response time (at the levels employed in most research that will be addressed here). Caffeine's impact on learning was examined under various conditions by Dr. Astrid Nehlig. 

Caffeine improved acquisition and recall in highly impulsive people following rhyming learning but decreased it after semantic acquisition, according to the test. Low-impulsive people's recollection was not consistently impacted by caffeine. In conclusion, coffee promotes learning when information is delivered passively; it has no effect on tasks where content is purposefully learnt.

Reference list

Borota, D., Murray, E., Keceli, G., Chang, A., Watabe, J.M., Ly, M., Toscano, J.P. and Yassa, M.A. (2014). Post-study caffeine administration enhances memory consolidation in humans. Nature neuroscience, [online] 17(2), pp.201–3. doi:https://doi.org/10.1038/nn.3623. 

Irwin, C., Khalesi, S., Desbrow, B. and McCartney, D. (2020). Effects of acute caffeine consumption following sleep loss on cognitive, physical, occupational and driving performance: A systematic review and meta-analysis. Neuroscience & Biobehavioral Reviews, [online] 108, pp.877–888. doi:https://doi.org/10.1016/j.neubiorev.2019.12.008. 

McLellan, T.M., Caldwell, J.A. and Lieberman, H.R. (2016). A review of caffeine’s effects on cognitive, physical and occupational performance. Neuroscience & Biobehavioral Reviews, [online] 71(1), pp.294–312. doi:https://doi.org/10.1016/j.neubiorev.2016.09.001. 

Nehlig, A. (2010). Is Caffeine a Cognitive Enhancer? Journal of Alzheimer’s Disease, 20(s1), pp.S85–S94. doi:https://doi.org/10.3233/jad-2010-091315. 

Nehlig, A. and Boyet, S. (2000). Dose–response study of caffeine effects on cerebral functional activity with a specific focus on dependence. Brain Research, 858(1), pp.71–77. doi:https://doi.org/10.1016/s0006-8993(99)02480-4. 

Pietrangelo, A. (2020). Yerkes-Dodson Law: How It Correlates to Stress, Anxiety, Performance. [online] Healthline. Available at: https://www.healthline.com/health/yerkes-dodson-law. 

Rodak, K., Kokot, I. and Kratz, E.M. (2021). Caffeine as a Factor Influencing the Functioning of the Human Body—Friend or Foe? Nutrients, [online] 13(9), p.3088. doi:https://doi.org/10.3390/nu13093088. 

Sherman, S.M., Buckley, T.P., Baena, E. and Ryan, L. (2016). Caffeine Enhances Memory Performance in Young Adults during Their Non-optimal Time of Day. Frontiers in Psychology, [online] 7(1764), pp.1–9. doi:https://doi.org/10.3389/fpsyg.2016.01764.