Source, serving size
|Drip 8 oz./ 237 mL||234|
|Percolated 8 oz./ 237 mL||176|
|Regular instant 8 oz./ 237 mL||85|
|Decaffeinated instant 8 oz./ 237 mL||3|
|Espresso 1 to 2 oz./ 30 to 59 mL||45 – 100|
|StarbucksTM Grande 16 oz./ 473 mL||330|
Cocoa and chocolate
|Cocoa from box 6 oz./ 170 g||10|
|Milk chocolate 1 oz./ 28 g||6|
|Baking chocolate 1 oz./ 28 g||35|
Soft drinks 12 ounces/ 355 mL
|Mountain Dew™ (US)||54|
|1 min brew||9 – 33|
|3 min brew||20 – 46|
|Instant||12 – 28|
|Iced tea 12 oz./ 355 mL||22 – 36|
|Red Bull™ 8.3 oz./ 245 mL||80|
|Monster™16 oz./ 473 mL||160|
|Rockstar™ 16 oz./ 473 mL||160|
|Redline™ Power Rush™ 2.5 oz./ 74 mL||350|
|Wired™ X505 24 oz./ 710 mL||505|
Humans have consumed caffeinated products for centuries. As far back as the Stone Age, we knew that eating seeds, leaves or parts of certain plants eased fatigue. Those on the Asian continent have drunk tea, or the extract of caffeine from the leaves, for several millennia. Coffee appears to have originated in the Middle East.
The use of coffee and tea eventually spread across the globe. Today, caffeine is the world’s most widely used stimulant. It is estimated that more than 120,000 tonnes are consumed each year.
Caffeinated products such as coffee and tea are often used to stimulate the central nervous system. It temporarily increases energy, alertness, and concentration, and gives feelings of wellbeing. Moderate caffeine use may even improve athletic performance.
Caffeine interacts with adenosine and dopamine, two of the systems that transmit nerve impulses. The adenosine system slows down the brain and causes drowsiness. Caffeine prevents the action of adenosine and helps to activate the nervous system. Dopamine is involved in the reward and pleasure centre of the brain. By increasing dopamine levels, caffeine elevates mood. It may also cause caffeine addiction.
The interaction between caffeine and the central nervous system means caffeine can make us anxious. As the nervous system is activated, it releases adrenaline, our ‘flight or fight’ response. This can cause tremors and anxiety, especially in those already suffering from anxiety disorders. As caffeine use can make us feel good, its withdrawal can also mimic symptoms of depression.
Several studies showed that drinking as little as two or three cups of coffee per day was associated with a lower risk of type 2 diabetes. The effect is similar for both caffeinated and decaffeinated coffee. This suggests an ingredient other than caffeine may be involved in the link with type 2 diabetes. At least one study showed that drinking six or more cups of green tea reduces the risk of developing diabetes. However, these studies are based on observation and do not prove a cause and effect relationship between caffeine and diabetes. Drinking coffee or tea is currently not recommended as a strategy to prevent diabetes.
Most studies have shown no relationship between caffeine intake and the risk of cardiovascular disease in men. However, in women, drinking two or more cups of coffee a day has been linked with a lowered risk of cardiovascular death.
In people who do not drink coffee often, caffeine can raise blood pressure by as much as 10 mm Hg. This increase is temporary. It likely reflects the activation of the nervous system. No link has been shown between chronic caffeine intake (up to six cups of coffee a day) and the risk of high blood pressure.
Coffee can contain kahweol and cafestol, both shown to increase cholesterol levels. During filtered coffee preparation, these chemicals can be removed by the filter paper. As a result, drinking filtered coffee is not usually associated with increased blood cholesterol.
In people with arrhythmias (abnormal heart rhythm) such as atrial fibrillation, average caffeine intake does not seem to interfere with the electrical activity of the heart. Unusually high amounts of caffeine may cause an abnormal heart rhythm in a person with cardiac disease.
It has been suggested that caffeine intake may be linked with a lower risk of colorectal (large bowel) cancer. Some research supports this idea. However, other more rigorous studies have not shown this link. Caffeine is not linked with the development of breast, prostate, ovary, bladder or pancreatic cancer.
Alcohol, viral hepatitis, iron overload and impaired glucose metabolism can all damage the liver. Coffee intake is associated with less risk of liver injury from these causes. Studies have also shown that the risk of cirrhosis and hepatocellular carcinoma (a type of liver cancer) is less for those who drink coffee. Caffeine users also seem to have a lower risk of some kidney cancers. As there is uncertainty in the research, caffeine use is not recommended as a way to reduce the risk of cancer.
The most apparent effect of caffeine on the kidneys is diuresis (increased production and passing of urine). At this time, no evidence suggests that caffeine damages the kidneys when up to three to four cups of coffee a day are consumed. However, higher amounts of caffeine could lead to kidney failure in some people.
(Aspirin™) and acetaminophen (Tylenol™), or diuretic medication simultaneously increases the risk. Those who have had calcium kidney stones and consume caffeine should drink more fluids to avoid developing stones.
Caffeine does not seem to lower bone mineral density. Several studies show that drinking four or more cups of coffee a day is linked to a greater risk of hip fracture. Adequate calcium and vitamin D intake, and limiting coffee to three cups a day, are essential to maintaining healthy bones.
Children are more at risk for behaviour changes caused by caffeine. Still, effects including nervousness, anxiety and disturbed sleep are generally not seen at doses less than 3 mg/kg of body weight. Health Canada recommends limiting the amount of caffeine given to children to 2.5 mg/kg of body weight. For a 15-kilogram child, this equals about 38 milligrams of caffeine, the amount in a can of cola or four chocolate brownies.
Caffeine may exaggerate changes that occur in pregnancy, like increased urine production or higher heart rate. These changes are generally harmless. Although there is great controversy on this topic, high amounts of caffeine (four or more cups of coffee) have been associated with delays in becoming pregnant. As well, the risk of miscarriage and low birth weight may also increase. It is reasonable for women who want to be or are pregnant to limit caffeine intake to 300 mg daily, about two to three cups of coffee.
Older adults may be more at risk when drinking caffeine. A number of medical conditions that commonly affect this age group may be made worse. These include bone fractures and urinary incontinence (difficulty holding urine). Caffeine may interact with common medications such as acetylsalicylic acid (ASA) and diuretics. Those who drink too much coffee or tea may also be at higher risk of malnutrition and lack vitamins and minerals.
Caffeine can enhance the effect of medications like epinephrine and albuterol/salbutamol (VentolinTM). It can also increase the effect of acetaminophen and acetylsalicylic acid. Talk with your family doctor about the safe amount of caffeine for you. Heart patients going for a cardiac stress test must not have caffeine for 24 hours beforehand.
Combining caffeine and ephedrine may enhance athletic performance. However, this combination could seriously affect the cardiovascular and central nervous systems. The safety of caffeine and ephedrine together has not been established. This is not a recommended way to excel in sport.
Caffeine overdose can result in agitation, seizures, difficulty breathing, abnormal heart rhythm, nausea, vomiting, and other problems. Intake of 15 to 30 milligrams of caffeine per kilogram of body weight (six to eight cups of coffee in a 75 kilogram adult) can result in toxic symptoms. Having more than than 100 mg/kg can be deadly.
Caffeine withdrawal can cause headaches, fatigue, drowsiness, irritability, difficulty concentrating and depressed mood.
Caffeinated energy drinks, such as Red Bull™, have become more popular over the last several years. This is especially true for college and university students. The main active ingredient in these beverages is caffeine. Use such drinks with caution. Health Canada recommends limiting Red Bull™ to two cans a day. Most importantly, it should not be mixed with alcohol. The combination can mask symptoms of intoxication, causing injury.
Caffeine may be linked with health benefits such as reduced risk of diabetes and liver cancer. However, scientific evidence does not support using it as a way to reduce the risk of these conditions. A healthy lifestyle that includes a well-balanced diet and adequate physical activity is a much better strategy.
Caffeine can boost alertness, mental concentration and energy levels. Still, it would be best to limit intake to 300 mg per day (two to three cups of coffee) for adults. Children should have no more than 2.5 mg/kg (a can of cola for a 15-kilogram child). If you have health problems, discuss your caffeine intake with your doctor.