Coffee lovers think they know how to start the day right: a whistling noise of the coffee machine then comes to the scent of freshly brewed espresso coffee. A special, the early morning, coffee flavor. Which makes billions of cups drunk daily. The rest is history.
What coffee beans are made of?
Caffeine (1, 3, 7-trimethylxanthine) is the main coffee ingredient, among nearly 1000 of others, ‘guilty’ for the alertness and many other effects it has on our body. It is also present in tea, chocolate, cocoa beverages, soft drinks, energy drinks, medications, specialized sports foods and supplements, skin care products, body creams, shampoos, soaps, and more. As we can see, the exposure to caffeine can be via skin and/or consumption of other caffeinated drinks. Not just by drinking tea and coffee!
Interestingly, the first mentions of caffeine in 1025, reads that coffee was used as a skin cleanser and for better body odor! It was only later that its popularity grew due to its ability to induce wakefulness or for keeping us awake at night.
Caffeine has several mechanisms of action. The most famous is the blockade of adenosine receptors: the negative inotropic (strength of contraction of heart muscle) and the chronotropic effect (heart rate) of adenosine. That leads to increased contractility of the heart muscle and the heart rate (heartbeats per minute), which occurs due to inhibition of enzymes called phosphodiesterase and the mobilization of intercellular calcium. Therefore, the volume of blood pumped by the ventricles (heart’s chambers) also increases, as well as blood pressure, temporarily, though.
Adenosine receptors – adenosine binds to them, creating a negative inotropic and chronotropic effect, ie. it slows down the work of the heart and reduces the force of contraction of the heart muscle.
If caffeine binds to these receptors and blocks them, then the opposite effects will occur – increased strength of contraction of the heart muscle and accelerated heart rate.
In other words, caffeine prevents adenosine from activating these receptors.
In addition to this, caffeine also blocks enzymes called phosphodiesterases and leads to the mobilization of intracellular calcium. As a result, there is an increased force of contraction of the heart muscle and accelerated heart rate.
However, it is established by various studies that there is no significant increase in blood pressure (BP), during exercise or at rest, in health, younger people after caffeine consumption. Which is not the case with obese individuals. Caffeine consumption increases blood pressure in those who already have elevated BP levels, or are known to be at higher risk of hypertension.
In the brain, it induces the release of dopamine and glutamate neurotransmitters, that is, it acts as a stimulant. It has a similar effect as other psychostimulants, i.e., nicotine, that participate in the ‘rewarding’ system by raising beta-endorphins, dopamine levels, as well as norepinephrine (noradrenaline) in the part of the brain called Nucleus Accumbens. Therefore, caffeine consumption carries dependence potential similar to addictive drugs, like cocaine and opiates.
The alertness effect of coffee is thanks to the secretion of the stress hormones by the adrenal gland. Originally, these chemicals are supposed to be released in reaction to physical threats that put us in a survival, autosave mode. But, researchers claim that adding little stress to our life, by drinking coffee, can actually positively affect parts of the brain responsible for memory, behavior, and emotions.
However, a long-term, force increase in adrenalin production, with symptoms like restlessness, sleep deprivation, nervousness, like being literally on the edge so to speak, means only one thing: we better start watching our daily caffeine doses!
Caffeine On Body & Mind
Based on experimental results in the literature, the main effects of caffeine can be divided into two groups:
- Cardiovascular effect and
- Effect on the central nervous system (CNS)
As mentioned before, adenosine acts as a negative chronotropic and inotropic agent at low doses of coffee. By blocking adenosine receptors, which increases heart rate, it could be expected that caffeine cause tachycardia and arrhythmias. As these expectations are confirmed in animal studies, results from human studies found that drinking low doses of coffee doesn’t increase the risk for dangerous heart arrhythmias during the exercise or at rest, in healthy young adults.
Additionally, a reduction in cardiovascular disease risks was reported (atherosclerotic cardiovascular disease, coronary heart disease, stroke, etc.), when up to 3 cups of coffee per day were consumed (about 300–400 mg/d of caffeine).
However, according to another study, consumption of coffee exceeding recommended daily doses (up to 4 cups/400 mg/d of caffeine) has been linked to double the risk of affecting hearth chambers responsible for pumping the blood throughout the body. Consequently, a higher rate of sudden cardiac death in patients with a history of coronary artery disease after drinking 9 or more coffee cups daily is reported.
Neurodegenerative diseases prevention
Researchers also found that (healthy) elderly patients can boost their memory and protect themselves from the risk of cardiovascular mortality by drinking a small amount of coffee on a regular basis.
In line with previous findings, some recent studies have linked regular consumption of low doses of caffeine to reduced risk for neurodegenerative diseases: Alzheimer’s and Parkinson’s. For Parkinson’s disease results differ for men and women due to the presence of estrogen in women (because estrogen interacts with caffeine, men actually see better improvements).
This is confirmed by animal-testing research: when the mice were given a low to medium dose of caffeine, it was noticed that there was an improvement in memory and motor function. However, when a high dose was administered, the opposite effects on memory, such as learning difficulties and anxiety, occurred.
However, a significant difference in the metabolism, clearance, and elimination of caffeine, that is, an individual’s tolerance to caffeine, could be the reason for different metabolic responses. In other words, what works for some people, may not work for others. For example, metabolism may slow down in pregnancy and women taking birth control pills. On the other hand, smoking can accelerate caffeine metabolism. Also, some individuals can develop caffeine tolerance, which means that by drinking coffee regularly the stimulatory action of caffeine does not trigger the stimulative response and an increase in blood pressure.
Therefore, it can be concluded that low intake of caffeine does not seem harmful to the cardiovascular system, and can even be beneficial; but higher doses of caffeine can cause severe reactions in people who already have certain conditions. In pregnancy, for example, recommended daily doses of caffeine should not exceed 300 mg per day (3 cups), i.e., 200 mg per day for women who are likely to have a high-risk pregnancy.
Low doses for better performance
The mild psychoactive effect of caffeine on the CNS is the main reason for its widespread use. The most famous are those promoting wakefulness and the performance effects, such as (temporary) increased locomotor activity (coordination of muscle movement, etc.) and intellectual stimulation. Admittedly, these effects are dose-dependent and confirmed after a low dose of caffeine is administered. Perhaps, this is the reason why this stimulant is not banned in sport. However, too much caffeine induces anxiety (restlessness, tension, increased heart rate, insomnia, worrying, etc.).
Another study found regular caffeine consumption (again, at low doses) hepatoprotective, with potential to reduce the risk of severe liver diseases such as cirrhosis, hepatocellular carcinoma, and other metabolic diseases (like type 2 diabetes), due to anti-inflammatory and antioxidant activity of caffeine, i.e., its phenolic compounds. Again, this is only in theory, the pathways are not fully understood.
Additionally, drinking too much coffee is often thought to be associated with stomach discomforts such as heartburn, indigestion, and ulcer. However, for gastric ulcers, duodenal ulcers, reflux esophagitis, and non-erosive reflux disease scientific results are inconclusive.
Caffeine Addiction & Overdose
The development of caffeine tolerance during habitual coffee drinking means an increase in dose to experience the same stimulating effect. However, as dependence on caffeine develops, the increase of cardiovascular responses, such as blood pressure, after caffeine ingestion, will be greatly reduced.
For nonhabitual coffee drinkers, however, the vulnerability to caffeine intoxication is significantly higher. Also, consumption of other energy drinks may increase the risk of caffeine overdose. Symptoms of caffeine intoxication include anxiety, agitation, restlessness, insomnia, gastrointestinal disturbances, tremor, tachycardia, and in severe cases life-threatening conditions like heart attack and stroke.
Regarding caffeine’s dependence and abuse and its possible detrimental effects on human health, more research is needed, with the issues subsequently covered by appropriate regulation. Withdrawal symptoms (symptoms which occur when coffee intake is interrupted after chronic consumption) include headache, fatigue, increased heart rate, sweating, nausea, and tremor. Headache and fatigue reach a peak 12-24 hours after the last dose and can persist for one week.
To drink or not to drink, that is the question?
Common (Sense) Facts & Challenges
- Coffee is roasted at 180°C – 205°C (356°F – 401°F), which means the baking releases cancerogenic substances such as acrylamide.
- During the metabolism of coffee, intercellular calcium is forced out of the cell, what is left for the bones then, especially with chronic drinkers?
- If coffee drinking accelerates heart rate, does it mean that the heart loses its natural rhythm? How that can be beneficial?
Another source of uncertainty regarding beneficial effects of coffee is the fact that these plant-based, insufficiently researched, compounds in coffee beans can be highly poisonous, to the degree that they can act as an insecticide, for the plant own protection. To illustrate this point it is enough to say that when dead coffee leaves drop to the soil, it prevents other seeds germinating. That’s why some people use leftover coffee grounds to control weeds in their gardens.
But, according to Victor A. Albert, an evolutionary biologist from University at Buffalo, there is also a positive side: nectar in the flower of the coffee plant and other plants, make insects, like bees, more likely to remember it and come back for more, so they can spread their pollen further. In other words, caffeine is insect-attracting for a good purpose.
“I wouldn’t be able to do all this fabulous work on coffee if it weren’t for the coffee itself”, the scientist admits, adding that “it wakes me up every morning”.
So, by keeping our doses low, we can retain only pleasant experiences and look forward to the morning show again. Just like bees.
Otherwise, consuming too much caffeine would certainly change our brain chemistry and we might start experiencing dependency symptoms.
However, the truth is that scientists know little about the combined effects of chemicals in coffee, and their potential toxicity in larger amounts. And, until we gather more information and evidence on their extraordinary complex pathways in our body, we better limit the caffeine intake.
And for coffee lovers, why not end this article with interesting news on cold and hot brew coffee?
A recent study investigated acidity and antioxidant activity of cold-brew coffee to compare results to that of hot-brew coffee. The researchers evaluated differences in the acidity and antioxidant activity as a function of brewing temperature and time. They concluded that cold brew coffee has lower concentrations of acidic compounds and is less chemically diverse. While their pH values are comparable, hot brew coffee has higher antioxidant activities than cold brew coffee, which means that hot brew has higher potential to prevent tumor growth, biliary cholesterol crystallization, and formation of gallstones. Again, this is only in theory.
In the meantime, we should carefully listen to the signals our body sends us (like, for example, heart palpitations or sleep deprivation), to determine how much coffee is too much. But, we need to have in mind that chronic, long term consumption of higher doses of caffeinated drinks significantly increase the risk of tolerance and addiction. And this is the clear case where more doesn’t mean better. On the contrary.
By Sanja Petrovic, MSc Pharmacy
Edited by firstname.lastname@example.org
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- Rao, N.Z., and Fuller, M. (2018). Acidity and antioxidant activity of cold brew coffee. Sci. Rep. 8: 16030