Caffeine. One of the few substances on Earth that I am sure most people say they could not do without. Whether it is coffee, energy drinks, teas or just munching on a handful of chocolate-covered espresso beans, it is being taken in by roughly 90% of the world’s population on a daily basis. This beats out the 29% that drink alcohol or the 25% of the world population that uses nicotine. It also makes coffee the most consumed psychoactive drug (and the most socially acceptable one). In this Fascinating Friday, we delve into the way that our body takes in caffeine and its physical and psychological effects.

Caffeine is classified as a stimulant, meaning that it increases the activity of the central nervous system and the body in general. Specifically, it falls in the methylxanthine class of stimulants, which is joined by similar substances, such as theobromine (interestingly both found in chocolate and synthesized by the human body after ingesting caffeine) and theophylline (which is found in teas like yerba mate and the kola nut). In its pure form, it is a bitter, white crystalline powder. It is closely related in structure to adenine and guanine, which are two of the base nucleotides in our DNA and RNA. In the brain, there is a large nucleotide molecule called adenosine, which uses adenine as a base when is attached to a sugar molecule, ribose. You may have heard of adenosine in your school biology classes, where it was commonly represented in the compound adenosine triphosphate or ATP, the energy storage molecule of the body. Because caffeine is similar to this prevalent molecule in our bodies, it has an increased ability to bind to the same receptors in the brain. This means that it inherently blocks the ability of adenosine to bind to their receptors, but also increases the base nerve activity. This is what gives you those coffee jitters, leaving you feeling more awake and energetic.

The effects after intaking caffeine happen quickly, potentially due to the similarities of its chemical makeup and our base DNA nucleotides, and the effects on the human body can be felt within an hour of taking the substance. It is fairly soluble in its pure form, with water at body temperature being able to absorb around 20g/L before being too saturated to absorb more. However, with an increase in water temperature (at most to just below boiling) and the presence of an acid (which coffee beans provide), the solubility increases greatly. By the time you are taking your first sip of a freshly brewed cup of coffee, the new concentration of caffeine can be up to 660 g/L. In comparison, salt placed in nearly boiling water can only take in 359g/L before dropping out of the solution. Caffeine affects the CYP1A2 enzyme, which is a primary enzyme in the detoxification of the body, found primarily in the liver. This can result in a change in the efficacy of certain medications, as routine caffeine intake can result in up to a 20% decrease in the CYP1A2 enzyme efficacy.

***For a real-world example, coffee is shown to reduce the efficacy of escitalopram oxalate (more commonly known as Lexapro) by 28% in human trials. It also affects the intake of necessary vitamins and minerals. Iron absorption after caffeine intake can be decreased from 39%-90% after a single cup of coffee. Conversely, some medications have higher concentrations in the body after caffeine intake: taking a 650mg tab of aspirin with caffeine (120mg, or a cup of coffee) shows a peak of ~60 micrograms per milliliter vs. a peak of ~45 micrograms per milliliter, an 33% increase.***

The physical effects of caffeine show that it can increase performance in aerobic sports, especially those that require prolonged endurance. These athletes show delayed symptoms of muscle and central nervous system fatigue, meaning that they can operate for longer at that increased effort level before needing to take a break. For individuals that are considered to have lower physical fitness, it is shown to have an increased effect on the oxidation of fatty acids, meaning that it breaks down fat quicker. This happens due to the increase of hormone-sensitive lipase (HSL and an enzyme that breaks down fats) and inhibits glycogen phosphorylase (which is the enzyme that is used to break down polysaccharides or carbohydrates in the body. Because of this, there are higher levels of glycogen in the muscles after exercise, which means the body can potentially recover energy faster as these carbohydrate stores have not been depleted. Because of these potentially performance-enhancing aspects of caffeine, it was placed on the World Anti-Doping Association ban list from 1962 to 1972 and 1984 to 2003. It was removed in 2004 but is still monitored by the WADA because of its potential for misuse during competitive sports. Caffeine also causes diuresis, or excessive urination, which is a direct effect on the kidney at the adenosine receptors (similar to the effects in the brain).

Psychological effects of caffeine can range from person to person, depending on their particular caffeine sensitivity, but usually fall into general symptoms. In the Journal of Alzheimer’s Disease, it was shown that caffeine had been associated with decreased depressive symptoms and overall suicide risk. It also can increase alertness and increase emotional arousal (most noticeably in low caffeine users). However, it can work inversely. In larger doses or more sustained use, it has been shown that caffeine can increase anxiety-related symptoms, such as faster breathing, headaches, and increased sweating/pulse rate, and was placed in the DSM-5 as a subclass of Substance-Induced Anxiety Disorder (look for caffeine-induced anxiety disorder). It has also been classified as a potential cause of sleep disorders (reducing the slow-wave sleep in the early sleep cycle as well as a reduction in REM (rapid eye movement) sleep), eating disorders (increasing the metabolic rate and suppressing appetites) and possibly schizophrenic disorders (the adenosine receptors in the brain and the control of dopamine release).

Caffeine is a ubiquitous substance in our daily lives, and has helped many people with school, work, sports and more. But it is important to know the pros and cons of caffeine usage, no matter if you are casual tea drinker or downing multiple espresso shots before shooting out for the day. Always take all foods in moderation.