Coffee: Its Perks and Reasons to Be Bitter



The sweet and smoky fragrances of a cup of Joe in the morning (or afternoon, or at any time of the day really) rarely fail to arouse our senses and minds. It’s no wonder that 54% of Americans drink coffee every day. [1] Although many of the components are the same, coffee is prepared in a wide variety of ways that determine the balance of chemicals and nutrients that end up in your cup. Research shows that it can benefit many diverse bodily systems, but excessive consumption presents concerns, mostly because of the physiological and mental effects of caffeine. We introduce both the positive and negative health effects so you can make an informed decision on how much coffee consumption feels healthy for you.


THE anatomy of a cup of coffee


Nearly 99% of a cup of coffee! [2]

caffeine (or not)

Caffeine is a chemical compound naturally occurring in plants. Because it increases cognitive, motor, and involuntary functions, it is considered a stimulant. Caffeine works by blocking the adenosine receptor, so the molecule adenosine can’t bind and induce processes like sleep. It also increases dopamine, a signaling molecule in the brain which elevates energy and mood (see Dopamine Q&A in Volume 14, Issue 3). [3]

There are on average 100 mg of caffeine in an 8 oz cup, enough for a noticeable stimulant effect. The caffeine concentration can vary greatly by roast and brand. For example, 8 oz of plain Starbucks coffee (much less than their standard cup sizes) has as much as 180 mg of caffeine! [4]

Your cup of Joe may also be decaffeinated, meaning that the caffeine has been dissolved out of young coffee beans to produce what’s commonly known as decaf. However, an 8 oz cup of decaf may still contain anywhere from 2 to 12 mg of caffeine. [5]

aromatic compounds

Coffee is made up of around 850 different volatile compounds that easily evaporate and allow us to smell that distinct fragrance of coffee we know and love. These chemicals are produced in the process of roasting. [6]


Coffee contains lots of chlorogenic acid, up to 12% of dried coffee beans by weight. This and other acids contribute to the bitter taste of coffee. They also contribute to the deep brown hue of beans after roasting. [7] Acidity in the beverage does not necessarily mean you’ll feel acidic in your stomach, although coffee may provoke heartburn by stimulating production of body acids that tend to leak back into the esophagus in certain people. [8]


Polyphenols give many plants, including the coffee bean, their color and act as antioxidants. [9] Antioxidants are commonly lauded for protecting against cancer, maintaining vision, and reducing the risk of heart disease, although evidence is mostly inconclusive for all of these. [10] A variety of antioxidants in coffee are absorbed into the bloodstream and protect against damage from free radicals. [6] Free radicals (unpaired electrons) are extremely reactive and will break apart molecules in the body, but antioxidants absorb the damage by eliminating the radical (with an unpaired electron of their own). [11]

extras for taste

This accounts for all the things you add into your coffee after it’s been brewed, like cream, sugar, and flavorings. Coffee by itself has only about 2 calories per cup—but cream and sugar can add up to 50 calories of nutritionally-empty carbohydrates each. [12]


Diterpenes, a kind of fat present in coffee oil, can raise cholesterol. Instant varieties are especially high in diterpenes because there is no paper filter involved to absorb the fats. [6]


what determines the balance of these things?

The balance of the chemical components of coffee is influenced by inherent properties of the coffee bean and production techniques like roasting and brewing. Roasting is heating the beans at a temperature between 356 and 446°F for a given amount of time. The exact temperature depends on the roast being made. It brings out the bean’s flavors and scents by generating aromatic compounds. [13] Finally, brewing processes take roasted coffee grounds and steep them in water for anywhere from a few seconds to several hours to allow the compounds in coffee to mix into the liquid and make the beverage we know and love. [14] Below are descriptions of the variations in beans, roasts, and brewing techniques.



the bean


A species of coffee bean that constitutes about 75% of global coffee production. Common in specialty coffees. Thought to produce a superior taste. Lower in caffeine and less acidic than robusta, but higher in polyphenols and fats. [15,16]


A species of coffee bean that constitutes about 25% of global coffee production. Common in instant varieties. Easier to grow/more resilient and thus cheaper on the market. It is high in caffeine and acids, but low in polyphenols and fats.


the roast 


Dark brown or even black in color. Bitter, smoky taste. Produced by roasting beans at relatively high temperatures (437 to 446°F). Used to produce espresso or French roasts. Contrary to common intuition, darker roasts are the least concentrated in caffeine—the process of roasting actually breaks down caffeine naturally present in the beans. They’re also the least acidic and highest in fat. [13]


Medium brown in color. Roasted in the middle range of 410 to 428°F. Considered an intermediate between dark and light, with balanced flavor, aroma, and acidity. Also known as regular, American, or breakfast roast.

Light (or Blond)

Light brown in color. Best retains flavors of original bean with more acidic tastes. Roasted at relatively low temperatures (356 to 401°F) for shorter durations. May be called a cinnamon or New England roast. It has the highest caffeine content of the three roasts and is the most acidic.




Hot water is filtered through coffee grounds so the caffeine, fats, aromatic compounds, polyphenols, and acids are quickly dissolved into the water at an optimal temperature. Examples of this are standard coffee makers or French press. The result is a steaming, fragrant cup of Joe that is best consumed fresh as it begins to taste acidic and bitter as time passes. [6,14]


Instant coffee is coffee that has been pre-brewed and dried out and is often sold as powder or crystals. It can be dissolved directly into hot water and is quick to prepare. Instant coffee tends to contain high levels of fat that are dissolved straight into the beverage instead of being passed through the filter and have a reputation for being lower quality in terms of taste.

Cold brew

Coffee grounds are put into room temperature water and allowed to sit for anywhere between 3 and 24 hours. The solids are filtered out before serving. The cold temperature keeps the fragrant compounds from evaporating as quickly and reduces the amount of acids that can dissolve into the water. Cold brews end up very concentrated because of the long steeping time and the amount of coffee grounds used, so they are usually enjoyed diluted with milk or water.


health effects of coffee


+ increases attention and cognition

In low doses, coffee improves mental performance. A cup or two of coffee speeds reaction time to light stimuli, although adverse effects begin to set in after that point. One study found that coffee increased speed and accuracy in subjects taking a mock GRE exam. Another study observed that 200 to 400 mg caffeine, or 2 to 4 cups of coffee, decreased lapses in attention in a night-driving simulation. This effect is due to dopamine and other similarly structured signaling molecules. [17]

+ protects from neurodegenerative disease

Long-term coffee use correlates to a reduced risk of cognitive decline in old age and developing diseases like Alzheimer’s or dementia. [7]

- sleep disruption

Caffeine taken less than 6 hours before bedtime can reduce sleep time and quality of sleep. The study used a 400 mg dose, the equivalent of 2 large coffees or 4 small cups. [18]

- anxiety

Caffeine produces anxious behaviors when administered in high doses to rats. [19] In human experiments, men who rarely or never drink caffeinated beverages have increased blood pressure (a physiological indicator of anxiety) and higher self-reported anxiety ratings after drinking coffee. [20]

urinary system

- increases urination

Subjects drinking caffeinated coffee reported higher urgency and frequency to urinate when compared to controls who drank decaf. The effect is most pronounced among low-coffee users. Caffeine has a diuretic (water-expelling) effect in the body, so it causes dehydration but there is no evidence to say it’s pathological. [21]

digestive system

+ may reduce risk of type II diabetes

Both caffeinated and decaffeinated coffee were shown to correlate with reduced risk of type II diabetes, where the body fatigues its capacity to break down sugars. It’s thought that coffee enhances the ability of fat cells to take up sugar, and this effect may be due to chlorogenic acid. [22,23]

- can induce bowel movements

For certain individuals, coffee consumption can increase movement through the far end of the colon and induce a desire to defecate in as little as 5 minutes. The effect is independent of caffeine, meaning that traditional and decaf brews have the same effect. Coffee also stimulates the release of gastrin, a hormone known to facilitate contractions of the colon. This can be a positive effect, though, if you’re looking to “move things along.” [24]


+ fights bacteria

Polyphenols, present in high concentrations in high caffeine varieties of coffee, prevent binding of certain bacteria to the tooth surface. [25,26]

- stains enamel

Polyphenols are also responsible for the infamous brown tint of coffee-stained teeth. These compounds, responsible for the rich color of coffee, can deposit and bind directly onto the tooth surface. [27]


+ increases physical performance

In trained athletes and at high doses, caffeine improves performance during both short exercise intervals and longer physical activities. It increases overall force output, a measure of effort, and time to fatigue, a measure of endurance. One likely mechanism is breaking down fat for energy instead of relying solely on muscle energy stores. [28]

+ reduces risk of certain cancers

Various studies have reported that coffee consumption is linked to lower risk of melanoma, a cancer of the skin, and breast, liver, kidney, and colorectal cancers. [29,30] In animal studies, however, caffeine has been shown to both suppress and stimulate tumors. [7] Additionally, coffee also contains acrylamide, a potential carcinogen produced during roasting, but research on its effects are inconclusive. [6]

- raises cholesterol

A large-scale study in 1983 found that coffee consumption was associated with higher overall blood cholesterol and triglycerides and lower HDL, or good, cholesterol. This could be due to the diterpenes present in coffee oil. [6,31]



  • Feel free to enjoy your daily cup of Joe! The European Food Safety Authority (EFSA) says that it is generally safe to drink moderate amounts of caffeine (no more than 400 mg) on a daily basis. [32]

  • Take note of what coffee’s effects are for you personally—the amount of mental stimulation, anxiety, withdrawal, and gastrointestinal disturbances vary greatly from person to person.


the message to go

Coffee is a part of daily life for many of us and is a habit that has a lot of benefits for the body and mind. However, consumption should be limited to where the negatives don’t outweigh the positives. You should be able to understand what kind of coffee and how much suits you best and gives you the energy, cognition, and disease protection you need.


References ▾

  1. “Coffee by the Numbers.” (2016).
  2. “What’s Inside a Cup of Coffee?” (2009).
  3. “Caffeine.” (2016).
  4. “The Complete Guide to Starbucks Caffeine.” (2016).
  5. “Caffeine content for coffee, tea, soda and more.” (2014).
  6. “All about coffee.” (2016).
  7. “Chemistry in every cup.” (2011).
  8. “Pathogenesis of Coffee-Induced Gastrointestinal Symptoms.” NEJM. (1980).
  9. “Polyphenols as Natural Food Pigments: Changes During Food Processing.” Am J Food Technol. (2007).
  10. “Antioxidants: Beyond the Hype.” (2016).
  11. “Chemical and molecular mechanisms of antioxidants: experimental approaches and model systems.” J Cell Mol Med. (2010).
  12. “I’m trying to lose weight. Should I cut back on coffee?” (2014).
  13. “Coffee Roasts from Light to Dark.” (2016).
  14. “Coffee Brewing Chemistry: Hot Brew vs. Cold Brew.” (2014).
  15. “10 Differences between Robusta & Arabica Coffee.” (2014).
  16. “Comparative study of polyphenols and caffeine in different coffee varieties affected by the degree of roasting.” Food Chem. (2011).
  17. “Caffeine and human behavior: Arousal, anxiety, and performance effects.” J Behav Med. (1982).
  18. “Caffeine Effects on Sleep Taken 0, 3, or 6 Hours Before Going to Bed.” J Clin Sleep Med. (2013).
  19. “Anxiogenic action of caffeine: an experimental study in rats.” J Psychopharmacol. (1997).
  20. “Storm in a coffee cup: caffeine modifies brain activation to social signals of threat.” Soc Cog Affect Neurosci. (2011).
  21. “Prospective study on the effects of regular and decaffeinated coffee on urinary symptoms in young and healthy volunteers.” Neurourol Urodyn. (2015).
  22. “Coffee, Caffeine, and Risk of Type 2 Diabetes.” Diabetes Care. (2006).
  23. “Roles of Chlorogenic Acid on Regulating Glucose and Lipids Metabolism: A Review.” Evid Based Complement Alternat Med. (2013).
  24. “Effect of coffee on distal colon function.” Gut. (1990).
  25. “Antiadhesive Effect of Green and Roasted Coffee on Streptococcus mutans' Adhesive Properties on Saliva-Coated Hydroxyapatite Beads.” J Agric Food Chem. (2002).
  26. “Anti-cariogenic effects of polyphenols from plant stimulant beverages (cocoa, coffee, tea).” Fitoterapia. (2009).
  27. “Dental Discoloration: An Overview.” J Esthet Restor Dent. (2007).
  28. “Caffeine and Exercise Performance.” Sports Sci. (1996).
  29. “Coffee consumption and the risk of cutaneous melanoma: a meta-analysis.” Eur J Nutr. (2015).
  30. “Coffee consumption and the risk of cancer: An overview.” Cancer Lett. (2008).
  31. “The Tromsø Heart Study — Does Coffee Raise Serum Cholesterol?” N Engl J Med. (1983).
  32. “Scientific opinion on the safety of caffeine.” EFSA J. (2015).

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