Caffeine is used by the masses on a daily basis to increase wakefulness, alleviate fatigue, and improve concentration and focus.
In fact, caffeine is the most commonly used drug in the world.
Since caffeine is consumed so widely, there are a lot of half-truths, hearsay, urban legends, media hype, and even fiction surrounding the substance. In this article, we will clear up some of these misunderstandings.
Although the consumption of low to moderate doses of caffeine is generally safe and has proven health benefits, long-term excessive caffeine intake is a potential risk factor for certain health problems.
Contents of this article:
Fast facts on caffeine
Here are some key points about caffeine. More detail and supporting information is in the main article.
- At least 68 million Americans drink three cups of coffee every day.
- Over 21 million Americans drink six or more cups of coffee every day.
- It is believed that some 3 out of 4 regular caffeine users are "addicted" to the substance.
- Around 5 grams of caffeine can be fatal. This is the equivalent of 30-40 cups of regular coffee.
What is caffeine?
More than 90 percent of adults in the U.S. use caffeine regularly.
The Food and Drug Administration (FDA) describes caffeine as both a drug and a food additive; it is used in prescription and OTC medicines to treat tiredness, drowsiness, and to improve the effect of some pain relievers.
The chemical formula is C8H10N4O2. Caffeine can be prepared by extraction from natural sources or synthesized from uric acid.
Caffeine belongs to a group of medicines called central nervous system (CNS) stimulants. In conventional foods, caffeine can help restore mental alertness.
Caffeine's use as an alertness aid should only be occasional. It is not intended to replace sleep and should not regularly be used for this purpose.
In the U.S., more than 90 percent of adults use caffeine regularly, with an average consumption of more than 200 milligrams of caffeine per day - more caffeine than in two 6-ounce cups of coffee or five 12-ounce cans of soft drink.
Where is caffeine found?
Caffeine occurs naturally in the leaves, seeds, or fruit of more than 60 plant species, including:
- Coffee beans - seed
- Tea leaves - leaves, bud
- Kola nuts - seed
- Cacao beans - seed
- Guarana - seed
- Yerba mate - leaf
- Yoco - bark
Caffeine acts as a natural pesticide for plants; it paralyzes and kills insects that attempt to feed on them.
Caffeine no longer only features in tea, coffee, and chocolate; it is regularly added to gum, jelly beans, waffles, water, syrup, and more.
In response to the trend of "added caffeine" in a growing number of products, the FDA is investigating the safety of caffeine in foods and particularly its effects on children and adolescents.
"Energy drinks" with caffeine are considered by some to be aggressively marketed, particularly to young people, with additional products appearing on the market, from "psyched up" oatmeal to "wired" waffles.
Caffeine is even being added to marshmallows, sunflower seeds, and other snacks for its stimulant effect.
Caffeine content in products
For healthy adults, about 4 or 5 cups of coffee a day is an amount not associated with dangerous or negative side effects.
For healthy adults, the FDA has cited 400 milligrams of caffeine a day - about 4 or 5 cups of coffee - as an amount not associated with dangerous or negative side effects.
The FDA has not set an amount for children, but the American Academy of Pediatrics discourages the consumption of caffeine and other stimulants by children and adolescents.
The amount of caffeine included in some common foods and beverages are:
- Coffee, brewed - 102 -200 milligrams per cup
- Coffee, instant - 27-173 milligrams per cup
- Coffee, decaffeinated - 3-12 milligrams per cup
- Tea, brewed American - 40-120 milligrams per cup
- Tea, brewed imported - 25-110 milligrams per cup
- Tea, instant - 28 milligrams per cup
- Tea, canned iced - 22-36 milligrams per 12 ounces
- Caffeine-containing cola and other soft drinks - 36-71 milligrams per 12 ounces
- Cola and other soft drinks, decaffeinated - 0 milligrams per 12 ounces
- Cocoa - 3 - 13 milligrams per cup
- Chocolate, milk - 3-6 milligrams per ounce
- Chocolate, bittersweet - 25 milligrams per ounce
How does caffeine affect the body?
Caffeine binds to the same receptors as adenosine.
Whether caffeine is consumed in food or as a medicine, it changes the way the brain and body work. Once consumed, caffeine is absorbed into the blood and body tissues within around 45 minutes.
Caffeine is molecularly similar to adenosine, a chemical that is present in all human cells.
In the brain, adenosine acts as a central nervous system depressant.
In normal conditions, adenosine promotes sleep and suppresses arousal by slowing down nerve activity. Adenosine binding also causes blood vessels in the brain to dilate, to increase oxygen intake during sleep.
When awake, the levels of adenosine in the brain rise each hour.
To a nerve cell, caffeine looks like adenosine. Caffeine binds to the adenosine receptors. However, in contrast to adenosine, it does not decrease the cell's activity. As caffeine utilizes all the receptors adenosine binds to, the cells can no longer sense adenosine. As a result, instead of slowing down because of the adenosine level, cellular activity speeds up.
Caffeine blocks adenosine's ability to open up the brain's blood vessels, causing them to constrict - this is the reason caffeine is used in pain relief medicine for headaches. If the headache is vascular, the effect of caffeine narrowing the blood vessels can offer relief.
With caffeine blocking adenosine, there is an increase in excitatory neurotransmitters in the brain. The pituitary gland observes the increased activity and releases hormones that tell the adrenal glands to produce epinephrine. Caffeine's main effect on the body is an increased temporary sense of wakefulness and alertness, but it can also cause issues such as:
- Jitters and shakes
- Disrupted sleep
- Fast or uneven heartbeat
- High blood pressure
Once consumed, caffeine reaches peak level in the blood within 1 hour and remains there for 4-6 hours. Caffeine increases the release of acid in the stomach, sometimes leading to an upset stomach or heartburn.
Caffeine has been associated with increased urinary volume and frequency causing the body to lose water and electrolytes like potassium and sodium; however, studies show that caffeinated beverages in standard servings may not have a strong diuretic effect. There may be great variability in caffeine's diuretic property on different people.
Caffeine side effects
Heavy daily caffeine use - more than 500-600 milligrams a day - may cause side effects such as:
- Stomach upset
- Fast heartbeat
- Muscle tremors
Caffeine can interfere with the sleep cycle. Sleep loss is cumulative, and even small nightly decreases can add up and disturb daytime alertness and performance. The irony, of course, is that people often use caffeine as a way to improve alertness after a bad night's sleep.
Some medicines may interact with caffeine:
- Some antibiotics interfere with caffeine breakdown
- Theophylline: a bronchodilator - caffeine increases concentration of theophylline in blood
- Antiplatelet and anticoagulant drugs - aspirin, warfarin (Coumadin) and others - caffeine appears to have an antiplatelet effect, but this has not been confirmed in humans
- Beta-adrenergic agonists: ibuterol (Ventolin, Proventil) and isoproterenol (Isuprel) for instance - caffeine may increase the cardiac effects of these drugs
- Carbamazepine: caffeine reduces the bioavailability of this anti-seizure medication and could increase the risk of seizures
Caffeine is also thought to interact with other medications:
- Cimetidine (Tagamet)
- Clozapine (Clozaril)
- Dipyridamole (Persantine)
- Disulfiram (Antabuse)
- Diuretic drugs
- Flutamide (Eulexin)
A number of herbs and supplements can interact with caffeine to varying degrees; these include:
- Creatine: a combination of ephedra, caffeine, and creatine has been associated with ischemic stroke
- Ephedra: can increase the risk of serious, life-threatening effects such as hypertension, heart attack, stroke, and seizures - avoid taking ephedra with caffeine
- Red clover
Is caffeine addictive?
There has been much debate surrounding the question of whether caffeine is an addictive substance. In 2013, the American Psychiatric Association added caffeine withdrawal to the list of recognized conditions in the Diagnostic and Statistical Manual of Mental Disorders (DSM-V). Not all caffeine consumers suffer withdrawal symptoms, though.
Symptoms begin about 12-24 hours after sudden cessation of caffeine consumption and reach a peak after 20-48 hours. A gradual reduction in consumption over a period of days does not result in these symptoms.
Research has shown that caffeine does not activate the pathways in the brain that are related to addiction and reward in opposition to other drugs. Therefore, researchers conclude that caffeine is not an addictive substance.
Caffeine health benefits
Caffeine can improve physical performance during endurance exercise.
Studies have shown caffeine to have potential health benefits; some of these are discussed below.
Caffeine may boost weight loss or prevent weight gain, although there is no conclusive evidence to determine long-term results. Possible theories of how caffeine might affect weight include:
- Appetite suppression: caffeine may temporarily reduce the desire to eat
- Calorie burning: caffeine may stimulate thermogenesis - one method your body uses to generate heat and energy from digesting food
Weight loss products that are marketed as thermogenics may contain caffeine and ephedra (ephedrine).
The European Food Safety Authority (EFSA) concluded that there is a link between a 75 milligram serving of caffeine and both increased attention and alertness.
Taking a 160-600 milligrams dose of caffeine can improve mental alertness, speed, reasoning, and memory when subjects are fatigued. However, while caffeine can help recover alertness, it is not comparable to getting sufficient sleep.
Caffeine does not sober up someone who is drunk, nor does it make them fit to drive - it does not get rid of the effects of alcohol.
Caffeine can improve physical performance during endurance exercise.
The EFSA recognizes that caffeine can increase endurance performance, endurance capacity, and reduction in perceived exertion.
The effects of caffeine on short-term, high-intensity exercise remain inconclusive.
Caffeine works at adenosine receptors in the brain. Also, when caffeine is absorbed in the form of coffee, other compounds in coffee, such as polyphenol antioxidants, act on various pathways and may play an additional protective role.
Several studies suggest that regular, lifelong, moderate consumption of caffeine may slow down physiological, age-related cognitive decline, especially in women and those over 80 years old.
Alzheimer's and Parkinson's disease
Caffeine decreases the risk for age-related cognitive decline in diseases such as Alzheimer's and Parkinson's.
There are a wealth of epidemiological studies reporting an inverse association between coffee consumption and risk of Parkinson's disease.
Research from Johns Hopkins University suggests that a dose of caffeine after a learning session may help to boost long-term memory.
Liver and colon
Caffeine enemas may help prepare the colon for an endoscopy or colonoscopy by supporting the excretion of bile through the colon wall. Although proponents of coffee or caffeine enemas claim that this therapy increases the levels of glutathione (an antioxidant) and thereby supports the natural processes of detoxification in the liver, there is little evidence to support this theory.
There is evidence that coffee consumption is associated with decreased risk of cirrhosis and lower rate of disease progression in hepatitis C infection. Observational studies demonstrate a protective effect of coffee with regard to hepatocellular cancer.
Caffeine may help protect people from an eye disorder known as blepharospasm, according to a study published in the Journal of Neurology, Neurosurgery, and Psychiatry. The condition, caused by abnormal brain function, makes people blink incessantly and can leave them functionally blind.
Researchers from the University of Maryland School of Medicine in Baltimore, MD, found that caffeine may be effective in protecting the lens against damage that could lead to the formation of cataracts.
A Rutgers study strengthens the theory that caffeine guards against certain skin cancers. Based on studies in mice, scientists believe that caffeine applied directly to the skin might help prevent damaging ultraviolet light from causing skin cancer.
In another study, researchers found that drinking three cups of caffeinated coffee a day was linked to a 21 percent lower risk of developing basal cell carcinoma in women, and a 10 percent lower risk in men, compared with drinking less than one cup per month.
A study of 217,883 participants analyzed the association between caffeine intake and the risk of developing kidney stones.
Mouth and throat cancer
In a study of 968,432 men and women, participants who reported drinking more than 4 cups of coffee a day had a 49 percent lower risk of death from oral cancer compared with those who drank no coffee at all or only an occasional cup.
Scientists examining data collected in Sweden about 34,670 women without a history of cardiovascular disease found that women who drank more than one cup of coffee per day had a 22-25 percent lower risk of stroke compared with women who drank less.
They found that low or no coffee drinking was linked to an increased risk of stroke.
Type 2 diabetes
In an analysis of data from three large studies, covering a 20-year period, researchers noted that participants who increased their coffee intake by more than one cup a day over a 4-year period had an 1 percent lower risk of developing type 2 diabetes compared with people who did not change their intake.
In addition, people who lowered their daily consumption by more than one cup of coffee showed a 17 percent higher risk for type 2 diabetes.
Further claimed health benefits of caffeine include:
- Decreased risk of endometrial cancer
- Reduced risk of prostate cancer
- Protection against head and neck cancer
- Helping to prevent the return of breast cancer
What are the health risks of consuming caffeine?
While much of the research published does allude to the safety and even potential benefits of caffeine (in moderation), there are a handful of research studies that highlight the potentially harmful effects of caffeine.
There is no clear link between caffeine intake and depression. However, caffeine intake and depression may be linked indirectly among people who are particularly sensitive to the effects of caffeine or who consume too much caffeine.
The effects of caffeine on blood glucose levels and insulin activity are highly variable among different people. There is some evidence that caffeine impairs insulin action but does not necessarily affect blood sugar (glucose) levels in young, healthy adults.
However, if you have type 2 diabetes, the impact of caffeine on insulin action may be associated with a small but detectable rise in blood sugar levels, particularly after meals.
Pregnant people are recommended to consume less than 300 milligrams of caffeine a day.
Studies in humans have shown that doses of caffeine greater than 300 milligrams (an amount equal to around three cups of coffee) a day may cause miscarriage or slow the growth of a developing fetus.
Also, use of large amounts of caffeine by the mother during pregnancy may cause problems with the heart rhythm of the fetus.
Those who are pregnant are recommended to limit caffeine to less than 200 milligrams a day.
Caffeine passes into breast milk in small amounts and may build up in the nursing baby.
Studies have shown that babies may appear jittery and have trouble sleeping when their mothers drink large amounts of caffeinated beverages.
Preliminary research suggests that an extra jolt or two of caffeine may trigger a gout attack in people with the condition.
Drinking six or more caffeinated beverages in 24 hours is associated with an almost four-fold increase in the risk of recurrent gout attacks.
In a study from the University of Alabama evaluating data on 1,356 women who reported taking in 329 milligrams of caffeine a day - about three cups of coffee or more - 70 percent had a higher likelihood of bladder problems.
Results from a study published in the Journal of Clinical Sleep Medicine showed that consuming caffeine 3 and even 6 hours before bedtime significantly disrupts sleep - even when consumed 6 hours before bedtime, it reduced objectively measured total sleep time by more than 1 hour.
A population-based study published in Neurology found that dietary and medicinal caffeine consumption appears to be a modest risk factor for chronic daily headache onset, regardless of headache type.
There is some research to suggest that caffeine reduces muscle activity in the fallopian tubes that carry eggs from the ovaries to the womb.
The authors of the study say that caffeine can reduce a woman's chances of becoming pregnant by about 27 percent.
A study published in the journal Menopause found that menopausal women who consumed caffeine had a greater degree of vasomotor symptoms including hot flashes and night sweats.
Dangers of mixing alcohol and energy drinks
Energy drinks are beverages that typically contain caffeine, other plant-based stimulants, simple sugars, and additives.
When alcoholic beverages are mixed with energy drinks, the caffeine can mask the depressant effects of alcohol. Alcohol also decreases the metabolism of caffeine, prolonging its effects.
Drinkers who consume alcohol mixed with energy drinks are three times more likely to binge drink than drinkers who do not report mixing alcohol with energy drinks. They are also twice as likely to report experiencing sexual assault, sexually assaulting someone else, riding with a driver who was under the influence of alcohol, being physically hurt or injured, and requiring medical treatment.
Ingesting massive doses of caffeine all at once should be avoided as it can cause numerous health problems.
Death by caffeine might sound unlikely, but it can and has happened.
The FDA knows of a 19-year-old college student who died after taking an overdose of caffeine tablets to stay awake. A caffeine tablet contains as much caffeine as one to three 5-ounce cups of coffee.3
A single teaspoon of pure caffeine is roughly equivalent to 25 cups of coffee. Pure caffeine is a powerful stimulant, and very small amounts may cause accidental overdose. Parents should be aware that these products might be attractive to young people.
The symptoms of a caffeine overdose include:
- Jitters, restlessness, and nervousness
- Increased heartbeat
- Heart palpitations
- Cardiac arrest
Studies suggest that moderate amounts of caffeine are not harmful. How much is moderate? One hundred to 200 milligrams (one to two 5-ounce cups of coffee) each day is the limit that some doctors suggest, but each person is different.
How caffeine affects people varies with their size, their sex, how sensitive they are to caffeine's effects, and any medications or supplements they may be taking. Experts agree that 600 milligrams (four to seven cups of coffee) of caffeine or more each day is too much.
The human body has evolved various mechanisms to reduce the likelihood of caffeine overdose by preventing excessive consumption. Well before reaching a toxic level of caffeine, a person would experience side effects such as nausea and vomiting that would prevent them from consuming additional caffeine.
Indeed, it would take 149 or so cans of caffeinated energy drink to kill an average adult male, meaning that vomiting would most certainly occur before a fatal overdose of caffeine.