What facts should I know about caffeine?
- Caffeine is a stimulant obtained from over 60 different types of plants worldwide.
- The scientific name for caffeine is 1,3,7-trimethylxanthine.
- Caffeine is considered to be the most commonly used psychoactive drug in the world.
- Coffee, soda, and tea are the most common sources of caffeine in the American diet.
- Discontinuation of regular caffeine use may produce withdrawal symptoms.
- The effects of caffeine persist for about three hours or less.
- Caffeine is found in some combination medications and weight control products.
- The American Medical Association and US Food and Drug Administration consider a moderate intake of caffeine to be "generally recognized as safe."
What is caffeine?
There are few people who are not aware of the stimulating effect that caffeine provides. We have a choice and choose caffeinated beverages for a reason. Caffeine is considered the most commonly used psychoactive drug in the world. A majority of adults consume it on a daily basis, and research is being done on its health benefits and consequences.
We may love our caffeine, but what exactly is it? Caffeine is the common name for 1,3,7-trimethylxanthine. When purified, caffeine produces an intensely bitter white powder that provides a distinctive taste in soft drinks. The word "caffeine" came from the German word kaffee and the French word café, each meaning coffee.
After ingesting caffeine, it is completely absorbed within 30 to 45 minutes, and its effects substantially diminish within about three hours. It is eventually excreted so there is no accumulation in the body. Caffeine has been shown to affect mood, stamina, the cerebral vascular system, and gastric and colonic activity. But caffeine may not be for everyone. This article will discuss the health benefits and consequences of caffeine.
What are the sources of caffeine?
Caffeine is naturally found in certain leaves, beans, and fruits of over 60 plants worldwide. Its bitterness acts as a deterrent to pests. The most common sources in our diet are coffee, tea leaves, cocoa beans, cola, and energy drinks. Caffeine can also be produced synthetically and added to food, beverages, supplements, and medications. Product labels are required to list caffeine in the ingredients but are not required to list the actual amounts of the substance.
The U.S. Food and Drug Administration (FDA) and the American Medical Association (AMA) classify a "moderate intake" of caffeine as "generally recognized as safe." This means that if you consume a moderate amount it is generally safe for the people on whom it has been studied. Most of these studies have been done on adults. Here is the definition of what is considered low, moderate, high, and heavy amounts of caffeine intake:
- a low to moderate intake is 130 mg-300 mg per day
- a moderate is 200 mg-300 mg per day
- high doses are above 400 mg per day
- heavy caffeine consumption is more than 6,000 mg/day.
It is estimated that the average daily caffeine consumption among Americans is about 280 mg/day, while some people consume more than 600 mg daily. The top three sources of caffeine in adults are coffee, soda, and tea.
One mistake that people make is assuming that decaffeinated means that there is no caffeine in the food or beverage. Decaffeinating happens through a process. According to the site Coffeeresearch.org, decaffeinating coffee usually consists of soaking the beans in water to dissolve the caffeine, extracting the caffeine with a solvent or activated carbon, and then re-soaking the beans in the decaffeinated water to reabsorb the flavor compounds that were lost in the initial extract.
A study published by the Journal of Analytical Toxicology found that nine out of 10 tested cups of decaf coffee from coffee from shops and restaurants contained 8.6 mg-13.9 mg of caffeine. It also found that decaffeinated espresso shots contained 3 mg-16 mg of caffeine per shot. Another study done by Consumer Reports tested 36 cups of small decaf coffees from six locations. They found that more than half had less than 5 mg of caffeine while the rest had a range from 20 mg-32 mg per cup. Depending on how much you consume in a day, you can end up consuming more caffeine from decaffeinated drinks than you would in one cup of coffee.
There is no way to know for sure exactly how much caffeine you consume so it's a good idea to put a limit on the total amount caffeinated and decaffeinated products that you consume. You can also choose products with lower caffeine contents. You won't find the content on the food labels, so refer to this chart. Make sure that you check the serving size on the can, bottle, or cup and do the math based on the serving size provided here:
|Caffeine source||Amount of caffeine|
|Plain, brewed coffee 8 oz||135 mg (range 102-200)|
|Instant coffee 8oz||95 mg (range 27-173|
|Espresso 1 oz||40 mg (range 30-90)|
|Plain, decaffeinated coffee 8 oz||5 mg (range 3-12|
|Green tea 8 oz||53 mg (range 40-120)|
|Black tea 8 oz||40-70 mg|
|Barq's root beer||22 mg|
|Coca-Cola Classic 12 oz||35 mg|
|Diet Coke 12 oz||47 mg|
|Dr. Pepper 12 oz||42 mg|
|Diet Dr. Pepper 12 oz||Data 44 mg|
|Jolt Cola 12 oz||72 mg|
|Mountain Dew regular or diet 12 oz||54 mg|
|Mountain Dew, MDX, regular or diet 12 oz||71 mg|
|Pepsi-Cola 12 oz||38 mg|
|Diet Pepsi 12 oz||36 mg|
|Sunkist Orange 12 oz||42 mg|
|Tab 12 oz||46.5 mg|
|Vault 12 oz||71 mg|
|Full Throttle energy dring 16 oz||144 mg|
|Monster Energy 16 oz||160 mg|
|Red Bull 8.5 oz||80 mg|
|Rip It energy drink 8 oz||100 mg|
|Sobe No Fear energy drink 8 oz||130 mg|
|Spike Shooter energy drink 8.4 oz||300 mg|
|Milk chocolate bar 1.5 oz||9 mg|
|Sweet chocolate bar 1.45 oz||37 mg|
|Cocoa powder mix 3 tsp||5 mg|
|Hershey's Special chocolate bar 1.45 oz||31 mg|
|Hot cocoa 8 oz||9 mg (range 3-15)|
|Jolt caffienated gum, 1 stick||33 mg|
|Ready-to-eat chocolate pudding 4 oz||9 mg|
|Ben & Jerry's Coffee Heath Bar Crunch 8 oz||84 mg|
|Ben & Jerry's Coffee Flavored Ice Cream||68 mg|
|Häagen-Dazs Coffee ice cream 8 oz||58 mg|
|Häagen-Dazs Coffee frozen yogurt 8 oz||58 mg|
|Excedrin Extra Strength, 1 tablet||65 mg|
|Bayer Select Maximum Strength||64.5 mg|
|Midol Menstrual Maximum Strength||60 mg|
|NoDoz Maximum Strength, 1 tablet||200 mg|
|Pain reliever tablets||65 mg|
|Vivarin 1 tablet||200 mg|
Is caffeine addictive?
Have you ever said that you can't function until your morning cup of coffee? Do you find yourself reaching for caffeinated coffee, tea, or soda when you are feeling lethargic? Could it be that you are addicted to caffeine? That all depends on whom you ask. Whether we consume caffeine for pleasure or purpose is a controversial topic. Those opposed to caffeine being addictive claim that we consume it for the pleasure of the product, while those who believe that it is addictive claim that we consume it for the purpose of satisfying our craving for it.
Psychiatric diagnoses are categorized by a manual published by the American Psychiatric Association called the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV). This manual covers all mental-health disorders for both children and adults. The DSM-IV does not classify substances as addictive but instead sets the criteria for substance dependence, including:
- substance-specific withdrawal syndrome;
- substance often taken in larger amounts or over a longer period than expected;
- persistent desire or unsuccessful efforts to cut down or control use;
- a great deal of time spent in activities necessary to obtain, use, or recover from the effects of the substance;
- important social, occupational, or recreational activities given up or reduced because of the substance; and/or
- use continued despite knowledge of a persistent or recurrent physical or psychological problem likely to have been caused or exacerbated by the substance.
In order for a user of a substance to be considered dependent upon it, the substance needs to meet at least three of the above criteria. It is clear that people can be dependent on caffeine based on these criteria.
Those who disagree with the idea that people can be dependent on caffeine point to the fact that studies do not show that 100% of people who consume caffeine experience symptoms of withdrawal or dependence. They also argue that people can often tell when caffeine is present by taste difference, so results of the studies are altered by that awareness. Instead of the addiction aspect they believe that the pleasurable aroma, taste, and social aspects of coffee are the reasons for consumption.
I don't know if we need to classify caffeine as addictive or something that you can be dependent on. I think that we need to be educated about the pros and cons of it in our diets and be aware of how our own body reacts to it. There is no doubt that there are withdrawal symptoms that you can experience. These symptoms include
- decreased energy/activeness,
- decreased alertness/attentiveness,
- decreased contentedness/well-being,
- depressed mood,
- difficulty concentrating,
- irritability, and
- feeling muzzy/foggy/not clearheaded.
The onset of withdrawal symptoms typically begins 12-24 hours after abstinence, with the peak intensity occurring at 20-51 hours. The withdrawal symptoms last for a range of two to nine days. This is a considerable amount of time that makes it easy to understand why people would have a hard time cutting caffeine from their diet.
There is no disputing the fact that caffeine "addiction" is not as intense or dangerous as drug addictions. You may feel "addicted" or dependent on it and it can be dangerous to overdo it. You can experiment and see how you feel with and without low to moderate amounts of caffeine. Some people do not feel anything when they consume caffeine and others don't feel anything when they stop consuming it.
For those who do feel the withdrawal symptoms it is best to slowly decrease your intake. Just as your body got used to the amount that you are consuming it will get used to less or none at all. All of this information is based on research done on adults. We can't say for sure that caffeine will have the same effect on children and adolescents without the proper research.
Is caffeine a diuretic?
Caffeine has been considered a diuretic by experts and consumers for years. Some people believe that drinking caffeinated beverages will cause them to lose fluids so they can't be counted as part of their daily intake. Others say that caffeinated beverages do not increase fluid losses. The best way to flush out the truth is to examine the research.
Each day our body has a need for water. We lose water through respiration, skin, renal, and gastrointestinal tract losses. Our intake of water comes from liquids and foods. We need to maintain an adequate water balance for our bodies to function properly. Factors such as age, activity level, health, diet, and environment can affect our water balance.
Some research has shown that caffeine intake can also affect our fluid balance. In one study, 12 caffeine consumers were told to abstain from caffeine for five days and were then given 642 mg of caffeine in the form of coffee. Their urine output increased when given the caffeine. Another study done on eight men tested the effect of 45 mg, 90 mg, 180 mg, or 360 mg of caffeine on urine volume. An increase in urine volume was seen only at the 360 mg dose of caffeine. One limitation to these studies is that they did not evaluate the impact of caffeine when consumed on a regular basis. A onetime dose may affect the body differently than daily consumption.
Back in 1928, caffeine was shown to have no significant impact on urinary output. Subsequent studies have shown that caffeine-containing beverages did not impact urinary output any differently than other beverages. Based on this, the Institute of Medicine recommends that "unless additional evidence becomes available indicating cumulative total water deficits in individuals with habitual intakes of significant amounts of caffeine, caffeinated beverages appear to contribute to the daily total water intake similar to that contributed by noncaffeinated beverages."
This doesn't mean that caffeine does not increase your need to urinate. Your reaction can depend on the amount that you consume, the type of product, and your tolerance level. If you have urinary incontinence, you may experience a greater "urgency" to urinate after consuming a caffeinated beverage. You will need to monitor your reaction and tolerance to caffeine to determine how you are affected. Water is still the recommended choice for optimal hydration, so be sure to include it as part of your daily fluid consumption.
How much caffeine is too much?
The amount of caffeine a product contains is not listed on the food label. If there were any dangers to consuming too much caffeine the law would require that the amount be listed, right? Unfortunately, this is a case in which the law hasn't caught up with reality.
We are consuming more caffeine than ever and the number of products that contain caffeine continues to grow. It used to be that coffee, tea, and cola were the only places where we got our caffeine. Now it's in supplements, medications, gum, candy, and energy drinks. People are reaching for their jolt of caffeine like they used to reach for their cigarette. We all eventually learned the truth about cigarettes and we are slowly learning the truth about excess amounts of caffeine.
The DSM-IV lists caffeine intoxication as a clinical syndrome. Caffeine intoxication is described by the following: recent consumption of caffeine and five or more symptoms that develop during, or shortly after, caffeine use including restlessness, nervousness, excitement, insomnia, flushed face, diuresis, and gastrointestinal complaints. People who do not consume caffeine regularly have a higher risk of this, but anyone who consumed more then what their body is used to or can handle is at risk.
Beyond intoxication there is death from "massive" doses of caffeine. A fatal dose for adults has been shown to be more than 10 grams, which would be drinking 80-100 cups of coffee in rapid succession. That may seem unlikely to happen, but there is now at least one report of death from too much caffeine.
A British man died after consuming caffeine powder at a party. The spoonfuls that he consumed were equal to consuming 70 energy drinks. The only "warning" that I found on one of these caffeine powders is "limit the use of caffeine-containing medications, foods or beverages while taking this product because too much caffeine may cause nervousness, irritability, sleeplessness and occasionally rapid heartbeat.
Do not give to children under 12 years of age. In case of accidental overdose, seek professional assistance or contact a poison control center immediately." On one online advertisement for a supplement, they actually brag about the fact that "one package of this product contains more caffeine than: 1,000 cups of coffee, 1,800 cans of Mountain Dew, 1,200 Red Bull Energy Drinks, or 4,000 cans of Coca-Cola Classic."
The reality is that it is possible to consume too much caffeine, and too much can mean death. The law needs to recognize this and require the caffeine content be listed on every product with a warning label about the dangers of consuming excess amounts.
Does caffeine cause heart disease?
With the high prevalence of heart disease, links between lifestyle factors, such as diet and physical activity, are undergoing extensive research. The original research into caffeine's role in this epidemic resulted in conflicting answers. Some evidence suggests an elevation in stress hormones from caffeine consumption that could pose a cardiovascular risk, but recent research has shown no relationship between caffeine ingestion and heart disease.
In fact, studies have actually shown a protective effect against heart disease with habitual intake of caffeinated beverages in the elderly population. The reason for the discrepancy may be due to the kind of beverage being consumed. Studies have shown that coffee and tea were not associated with increases in blood pressure or arrhythmias, while soft drinks were. Research also showed that decaffeinated coffee and tea did not provide the same benefits as the caffeinated versions.
The well-respected Framingham Heart Study examined all potential links between caffeine intake and cardiovascular disease and found no harmful effects from drinking coffee. There can, however, be exceptions to this. People react differently to caffeine, and some may experience elevations in blood pressure or arrhythmias. The blood pressure elevations are said to be short lived, lasting no more than several hours and are comparable to modest elevations experienced climbing a flight of stairs. It's always best to check with your physician if you are experiencing any side effects.
Does caffeine cause bone loss?
Too much of a good thing could be a problem for caffeine consumers. Evidence suggests that high caffeine intake may accelerate bone loss. One study found that elderly postmenopausal women who consumed more than 300 mg per day of caffeine lost more bone in the spine than women who consumed less than 300 mg per day. However, coffee and tea drinkers may be able to counteract this negative effect by adding milk to their beverage. The consumption of cola has also been shown to be associated with lower bone mineral density. While these studies were compelling, more evidence is needed to make a definitive decision about the role of caffeine and osteoporosis.
Does caffeine help with weight loss?
The weight-loss industry is estimated to be a $50 billion a year industry. Many people are looking for a way to get their piece of the money-making pie without a lot of credibility behind what they are promoting. The supplement industry is constantly promoting a new product to enhance weight loss by increasing satiety or burning fat. The claims are convincing, but the research backing many products is often lacking. To make matters worse, supplements often contain combinations of ingredients in the hopes of enhancing each one's effect without safety or efficacy tests. Caffeine is one of the ingredients now being included in many of the weight-loss supplements. It's added for its energy enhancement, appetite suppressant, and "fat-burning" properties.
The scientific evidence about caffeine as a weight-control agent is mixed. In a study done to monitor the impact of a green tea-caffeine combination on weight loss and maintenance, participants were divided into those who consume low levels of caffeine (<300 mg/day) and high-caffeine consumers (>300 mg/day). Weight loss was significantly higher in the high-caffeine consumption group, but weight maintenance was higher in the low-caffeine consumption group. The conclusion was that the caffeine was related to greater weight loss, higher thermogenesis, and fat oxidation, while the tea was responsible for the greater weight maintenance. Other studies have stated that caffeine actually contributes to weight gain by increasing stress hormones. It appears that caffeine's role in weight loss is as inconclusive as the efficacy of the majority of weight-loss supplements on the market.
Is caffeine safe during pregnancy?
There is no disputing the importance of proper nutrition during pregnancy. There is some dispute about the safety of caffeine during this time. One concern is that caffeine may lead to miscarriages. In a study following 431 pregnant women, no relationship between caffeine consumption up to 300 mg/day and adverse pregnancy outcomes was found. Another study examined the relationship between caffeine consumption and spontaneous abortions in over 5,000 women and found no association. A recent study found that caffeine can reach the follicular fluid of the ovaries. It also found that an increase in coffee consumption was associated with an increased number of aborted pregnancies.
On the other side, research has also shown no clear relationship between caffeine intake and fertility and birth defects. Even with this evidence, everyone agrees that there is a limit for how much caffeine can be consumed during pregnancy. The majority of the subjects in the studies were consuming small to moderate amounts of caffeine. It is difficult to accurately test the effects of very high intakes of caffeine without risking the health of the mother and child.. The American College of Obstetricians and Gynecologists recommends a caffeine limit of the equivalent of one to two cups of coffee per day during pregnancy.
Is caffeine safe for children?
With the increased popularity of coffee shops, a new generation of caffeine consumers was born. Children are being exposed to caffeine with products designed specifically to target them as early as 4 years of age. With the increase in caffeine-containing products, children can now be consuming as much caffeine as some adults. Could this trend be harming children?
Children and adolescents are the fastest growing population of caffeine users, with a large increase in the amount that they consume over the past 30 years. It is estimated that the average caffeine intake for children 2-11 years of age is 0.4 mg per kg of body weight each day, and those 12-17 years of age consume 0.55 mg/kg per day. This is almost half of what adults consume (1.3 mg/kg). These numbers are averages, so there are children and adolescents who are consuming even more than adults. The difference with adults and children is that there is research to show how much is acceptable for adults and what impact it will have on them when they go above that, but that is not the case with children. We can't be sure of the short-term or long-term effects of this kind of exposure to caffeine.
The Centers for Disease Control and Prevention's School Health Policies and Practices Study (SHPPS) 2000 survey concluded that 43% of elementary schools, 89.4% of middle/junior high, and 98.2% of senior high schools had a vending machine or a school store, canteen, or snack bar where students could purchase foods or beverages. The trend in milk consumption has declined over time, while soft drink consumption has risen. Studies have shown that children 2-18 years of age who consume over 9 oz of soda per day drink less milk and juice and end up consuming about 200 calories more each day compared to infrequent soda drinkers. Fortunately, this problem has gained a great deal of recognition, and some states have now enacted legislation to replace existing food and drinks of minimal nutritional value for healthier options or to restrict student access to the machines.
Companies are aware of the growing population of young caffeine drinkers. There are now products being marked directly to them. Energy drinks are the fastest growing segment of the beverage industry, and their marketing is often geared toward children and adolescents. Their caffeine content can be up to five times the amount of caffeine in one cup of coffee! Caffeine is also being added to water, gum, candy bars, potato chips, and oatmeal. A web site for a caffeine-containing gum makes this marketing statement:
"Each pack contains 12 pieces -- the energy/alertness boost of six coffees. Doing the math for you, a dozen packs contain a "makes-you-the-most-popular-kid-on-the block" 144 pieces of gum (72 cups of coffee). And you may be able to get Art History 101 credit by chewing Spearmint Gum. Each piece is a brilliant shiny white with green Jackson Pollock-ish speckles."
With all of these products, just imagine how easy it would be for a child to consume dangerous amounts of caffeine without anyone even realizing it. We have evidence for how much is fatal for an adult but do not know what that would be for a child.
The effect of caffeine on children's moods and behavior is another concern. In a study done by the National Institute of Mental Health, 8- to 13-year-olds who regularly consumed high doses of caffeine were judged to be more restless by teachers, and one-third were hyperactive enough to meet the criteria for attention deficit disorder with hyperactivity (ADHD). A Stanford study of fifth- and sixth-graders deprived of daily caffeine reported them as having symptoms that included trouble thinking clearly, not feeling energetic, and getting angry. These symptoms were even reported by children who typically consume 28 mg of caffeine a day. The research in this area is somewhat limited, but the studies that have been conducted are compelling enough to warrant restricting caffeine intake in children to as little as possible. If there is no nutritional need for caffeine, why take the risk and allow children to consume it?
How much fluid do we need?
Anyone who has ever been on a diet will tell you that you are supposed to drink at least 8 cups of water a day. Everyone knows this, but finding the evidence to support it is another story. In 2004, the Food and Nutrition Board established recommendations on the intake of water. The recommendations were set based on the necessary amount needed to maintain health and reduce chronic disease risk:
- The vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide.
- The report did not specify exact requirements for water but set general recommendations for women at approximately 2.7 L (91 oz) of total water (from all beverages and foods) each day and men at an average of approximately 3.7 L (125 oz daily) of total water.
- The panel did not set an upper level for water.
- About 80% of people's total water intake comes from drinking water and beverages (including caffeinated beverages), and the other 20% is derived from food.
- Prolonged physical activity and heat exposure will increase water losses and therefore may raise daily fluid needs, although it is important to note that excessive amounts of fluid can be life threatening. Acute water toxicity has been reported due to rapid consumption of large quantities of fluids that greatly exceeded the kidney's maximal excretion rate of approximately 0.7 to 1.0 L/hour.
The report allows all fluids to be counted into your total intake, so people began eliminating water from their diets in favor of other liquids. However, the recommendations were not intended to reduce water consumption. Water should be your primary source of fluid. Our bodies are made up of over 60% water, not coffee, tea, juice, or soda. Caffeine is a treat that will have health consequences when consumed in excessive amounts and is not safe for everyone. Set limits on the treats that you allow yourself, and be sure to give your body what it needs in adequate amounts. Too much of anything is just too much for our bodies to handle.
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Al-Saleh, I, I. El-Doush, B. Grisellhi, and S. Coskun. "The Effect of Caffeine Consumption on the Success Rate of Pregnancy as Well Various Performance Parameters of In-Vitro Fertilization Treatment." Med Sci Monit. 16.12 Nov. 2010: CR598-605. American Beverage Association
American Heart Association
Center for the Science in the Public Interest
"Children Increasingly Consuming Caffeine." National Drug Strategy Network. May-June 1998. <http://ndsn.org/mayjun98/caffeine.html>.
Cohen, D.L. J Clin Hypertens. 8.10 Oct. 2006: 744-745.
"Is It Really Decaf?" Consumer Reports. Nov. 2007. <http://www.consumerreports.org/cro/food/beverages/coffee-tea/is-it-really-decaffeinated-coffee-11-07/overview/decaf-coffee-ov.htm>.
"Caffeine Content of Food & Drugs." Center for Science in the Public Interest. Sept. 2007. <http://www.cspinet.org/new/cafchart.htm#table_coffees>.
Department of Health and Human Services
Diepvens, K. Am J Physiol Integr Comp Physiol. 292.1 Jan. 2007: R77-85.
Dixit, A. Indian J Phsyiol Pharmacol. 50.2 Apr.-June 2006: 175-180.
Dulloo, A.G. Am J Clin Nutr. 70.6 Dec. 1999: 1040-1045.
Eddy, N.B. J Pharmacol Exp Ther. 33 (1928): 167-174.
Fray, C.D. J Amer Diet Assoc. 105 (2005): 110-13.
Goldstein, A. Exp Clin Psychopharmacol. 5.4 Nov. 1997: 388-392.
Grandjean, A.C. J Am Coll Nutr. 19.5 Oct. 2000: 591-600.
Greenberg, J. Int J Obes (Lond). 29.9 Sept. 2005: 1121-1129.
Greenberg, J.A. Am J Clin Nutr. 85 June 2007: 392-398.
Harnack, L. J Am Diet Assoc. 99 (1999): 436-441.
Howland, J. Addiction. 106.2 (2011): 335-341.
Hughes, J.R. Am J Psychiatry. 149.1 Jan. 1992: 33-40.
Iso, H., et al. "The Relationship Between Green Tea and Total Caffeine Intake and Risk for Self-Reported Type 2 Diabetes Among Japanese Adults." Ann Intern Med. 144.8 Apr. 18, 2006: 554-562.
Juliano, L.M. Psychopharmacology. 176.1 Oct. 2004: 1-29.
Kendler, K.S. Am J Psychiatry. 156.2 Feb. 1999: 223-228.
Lane, J.D. Psychosom Med. 552.3 May-June 1990: 320-326.
March of Dimes
Maslova, E. Am J Clin Nutr. 92.5 Nov. 2010: 1120-1132.
National Academy of Sciences
Neuhauser-Berthold, M. Ann Nutr Metab. 41 (1997): 29-36.
Noordizij, M. J Hypertens. 23.5 May 2005: 921-928.
Ogawa, N. Psychiatry Clin Neurosci. 61.3 June 2007: 263-268.
Passmore, A.P. Clin Sci. 72 June 1987: 749-756.
Rapuri, P.B. Am J Clin Nutr. 74 Nov. 2001: 694-700.
Satel, S. Am J Drug Alcohol Abuse. 32.4 2006: 493-502.
Schuh, K.J. Psychopharmacology. 130.4 1997: 320-326.
Smith, A.P. Hum Psychopharmacol. 20.6 Aug. 2005: 441-445.
Temple, J. Neurosci Biobehav Rev. 33.6 Jan. 2009: 793-806.
The Beverage Institute for Health and Wellness
Tucker, K.L. Am J Clin Nutr. 84.4 Oct. 2006: 936-942.
U.S. Department of Agriculture
Warner, Jennifer. "Decaf Coffee Isn't Caffeine-Free." WebMD. Oct. 11, 2006. <https://www.webmd.com/diet/news/20061011/decaf-coffee-isnt-caffeine-free>.
Westerterp-Plantenga, M.S. Obes Res. 13.7 July 2005: 1195-1204.
Winkelmayer, W.C. "Habitual Caffeine Intake and the Risk of Hypertension in Women." JAMA. 294.18 Nov. 9, 2005: 2330-2335.