Caffeine has been part of our diet for more than thousands of years. Historically, the most common sources of caffeine are coffee, tea and chocolate. In its pure form, caffeine was first extracted from cacao bean. Nowadays, caffeine is often obtained from processed products such as soft and energy drinks. The type of predominant caffeine source varies between different age groups and parts of the world.1 In the USA, more than 90 % of adults consume caffeine regularly, with the highest amounts taken by 50- 65 old consumers. Coffee represents the main caffeine source among American adults, while children obtain caffeine mostly through carbonated soft drinks. In Canada the pattern of caffeine consumption is similar, although Canadian children consume less caffeine than American ones. Based on the EFSA (European Food Safety Authority) reports, coffee represents the leading caffeine source among European adults as well. The exceptions are UK and Ireland, where tea is the most common caffeine source.2
Caffeine in processed products
Caffeine is commonly added to carbonated soft drinks. The US Food and Drug Administration (FDA), set the level of caffeine in these drinks not to be higher than 0.02%. A can of Coca-Cola contains 32 mg of caffeine, while a can of Diet Coke contains around 42 mg, according to the manufacturer.3 Scientific literature reports similar amounts for Coca-Cola (33.9 mg/12 oz, i.e. can of 355 ml), Diet Coke (46.3 mg/12 oz), Pepsi (38.9 mg/12 oz), and Diet Pepsi (36.7 mg/12 oz) among other carbonated soft drinks.4
Besides in soft drinks, caffeine is present in energy drinks which are largely consumed by adolescents. A substantial increase in the consumption of these drinks is detected in Western and Asian countries.5 Caffeine content in energy drinks can vary from none to more than 140 mg per serving.6 In other words, caffeine content in energy drinks may range from 14 to 35 mg per 100 ml, with mean caffeine content per serving around 102 mg. 7
Natural sources of caffeine
Caffeine is naturally present in fruits, beans and leaves of more than sixty plants. The most popular sources are coffee beans, namely Coffea Canephora (syn. Coffea Robusta) and Coffea Arabic. The content of caffeine in coffee depends on the roasting temperatures and the water volume used for the extraction of ground coffee. In general, a typical cup of coffee contain from 80 to 175 mg of caffeine, but this content may range from 48 to 317 mg per servings.8 Geographical origin and cultural traditions have great influence on caffeine content in a cup of coffee. Thus, one American coffee cup contains the similar amount of caffeine (316 mg) as three Turkish (336 mg) and five Espresso coffee cups (320 mg).9
Biological Effects of Caffeine
After being ingested, caffeine is rapidly absorbed into the circulatory system. Once it is absorbed, caffeine can reach all body tissues as it crosses the blood-brain, blood-placenta and blood-testis barrier. Caffeine represents the most commonly consumed neuroactive compound worldwide. It acts as a stimulant of the central nervous system. In other words, caffeine increases alertness, wakefulness and cognitive performance. Also, caffeine affects muscles, where it increases post-exercise accumulation of glycogen. Further on, this ensures faster recovery after the intense exercise. Caffeine reaches the cardiovascular system where it affects heartbeat and blood pressure.10
Health benefits of caffeine
Caffeine is well-known for its effects on memory and concentration enhancement, and physical performance improvement. It promotes both mental and physical alertness by acting antagonistically on adenosine receptors. This further affects the dopaminergic system. Caffeine regulates dopamine concentrations especially in brain parts responsible for attention. This is how caffeine increases vigilance, attention and reduce fatigue.11
Caffeine has the ability to reduce muscle pain and sensation of force. This decreases the perception of effort during exercise, and, hence, promotes sustained efforts during exercise. Also, caffeine stimulates post-exercise muscle glycogen resynthesis, which ensures faster recovery following intense physical activity.10
Caffeine influences energy balance, by increasing energy expenditure and decreasing energy intake. Thus, caffeine can be used as a regulator of body weight. It helps in the maintenance of body weight through its effects on energy intake, thermogenesis and fat oxidation.12 Caffeine increases fatty acid oxidation, i.e. lipolysis by switching the preference from glycogen to lipids as a main energy source.
There is strong evidence that caffeine reduces the risk of type 2 diabetes. According to scientific studies, coffee and caffeine can significantly decrease the type 2 diabetes incidence. More precisely, the incidence of diabetes can be decreased by 12 % for every 2 cups increment in coffee intake and 14 % for every 200 mg increment in caffeine intake.13
Caffeine acts protectively against main neurodegenerative disorders. Consumption of 3 to 5 cups of coffee per day at midlife leads to about 65 % reduced risk of Alzheimer’s disease and dementia later in life. Coffee drinkers have also lower risk of developing Parkinson’s disease, based on caffeine effects on dopaminergic neurons.10
Recommended doses and side effects
According to the EFSA habitual daily intake of caffeine up to 400 mg for adults and 3mg per kg of body weight for children and adolescents bring no safety concerns. Total daily intake for pregnant and breastfeeding women should not exceed 200 mg.2 Consumption of more than 20 mg/kg of caffeine represents potentially toxic amount, while potentially lethal dosage is more than 150 mg/kg.14
High doses of caffeine express negative effects on the cardiovascular system, which is primarily affected by caffeine toxicity. Caffeine over-consumption leads to disturbances in heartbeat such as arrhythmia and tachycardia. Besides fast heartbeats, high doses of caffeine, i.e. 500 to 600 mg per day causes nervousness, insomnia, upset stomach and muscle tremors.15 Pregnant women should be especially careful not to exceed the recommended daily dose (200 mg). Higher amounts may lead to preterm delivery, low birth weight babies, or some birth defects.
When to avoid caffeine?
Infants and children are better to stay away from caffeine intake, as well as certain adult populations.
If you have glaucoma, epilepsy, anxiety or trouble sleeping you should quit caffeine intake. Also, if you are dealing with heart problems, i.e. high blood pressure or irregular heartbeats, consider restricting or eliminating caffeine. Caffeine may interact with some medications. For instance, caffeine might inhibit the metabolism of warfarin, and, hence, increase its blood concentration and anticoagulant effects. Thus, during warfarin therapy, you should limit the intake of caffeine-rich products.16 Importantly, caffeine should not be combined with other stimulant drugs since this leads to too much stimulation and serious side effects. Some antibiotics, as well as estrogens (births control pills), may slow down the caffeine break down and elimination from the body, and, thus, increase its blood concentrations.17
Caffeine makes everyday life easier with its stimulant effects. Also, caffeine brings numerous health benefits. In moderate amounts, caffeine promotes mental and physical alertness but reduces the risk of type 2 diabetes and neurodegenerative diseases as well. Still, we should all cautious not to exceed recommended doses. This is especially important in certain health conditions, such as pregnancy. When calculating our total caffeine intake, we should count not only cups of coffee or tea, but cans of carbonated soft and energy drinks as well.
- Verster JC, Koenig J. Caffeine intake and its sources: A review of national representative studies. Crit Rev Food Sci Nutr. 2018;58(8):1250-1259. https://www.tandfonline.com/doi/full/10.1080/10408398.2016.1247252
- EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). (2015). Scientific Opinion on the safety of caffeine. EFSA J. 13:4102, doi:10.2903/j.efsa.2015.4102
- Chou KH, Bell LN. Caffeine content of prepackaged national-brand and private-label carbonated beverages. J Food Sci. 2007;72(6):C337-342. https://www.ncbi.nlm.nih.gov/pubmed/17995675
- De Sanctis V, Soliman N, Soliman A, et al. Caffeinated energy drink consumption among adolescents and potential health consequences associated with their use: a significant public health hazard. Acta Biomed. 2017;88(2):222-231. https://www.ncbi.nlm.nih.gov/pubmed/28845841
- McCusker RR, Goldberger BA, Cone EJ. Caffeine content of energy drinks, carbonated sodas, and other beverages. J Anal Toxicol. 2006;30(2):112-114. https://www.ncbi.nlm.nih.gov/pubmed/16620542
- Keaver L, Gilpin S, Fernandes da Silva JC, Buckley C, Foley-Nolan C. Energy drinks available in Ireland: a description of caffeine and sugar content. Public Health Nutr. 2017;20(9):1534-1539. https://www.ncbi.nlm.nih.gov/pubmed/28438229
- Ludwig IA, Mena P, Calani L, Cid C, Del Rio D, Lean ME, Crozier A. Variations in caffeine and chlorogenic acid contents of coffees: what are we drinking? Food Funct. 2014;5(8):1718-1726. https://www.ncbi.nlm.nih.gov/pubmed/25014672
- Derossi A, Ricci I, Caporizzi R, Fiore A, Severini C. How grinding level and brewing method (Espresso, American, Turkish) could affect the antioxidant activity and bioactive compounds in a coffee cup. J Sci Food Agric. 2018;98(8):3198-3207. https://www.ncbi.nlm.nih.gov/pubmed/29230816
- Cappelletti S, Piacentino D, Sani G, Aromatario M. Caffeine: cognitive and physical performance enhancer or psychoactive drug? Curr Neuropharmacol. 2015;13(1):71-88. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4462044/
- Meeusen R, Roelands B, Spriet LL. Caffeine, exercise and the brain. Nestle Nutr Inst Workshop Ser. 2013;76:1-12. https://www.ncbi.nlm.nih.gov/pubmed/23899750
- Harpaz E, Tamir S, Weinstein A, Weinstein Y. The effect of caffeine on energy balance. J Basic Clin Physiol Pharmacol. 2017;28(1):1-10. https://www.ncbi.nlm.nih.gov/pubmed/27824614
- Jiang X, Zhang D, Jiang W. Coffee and caffeine intake and incidence of type 2 diabetes mellitus: a meta-analysis of prospective studies. Eur J Nutr. 2014;53(1):25-38. https://www.ncbi.nlm.nih.gov/pubmed/24150256
- Pendleton M, Brown S, Thomas CM, Odle B. Potential toxicity of caffeine when used as a dietary supplement for weight loss. J Diet Suppl. 2013;10(1):1-5.
- Zafar S, Ashraf MM, Ali A, et al. Effect of caffeine on anti-clotting activity of warfarin in healthy male albino rabbits. Pak J Pharm Sci. 2018;31(2(Suppl.)):611-616. https://www.ncbi.nlm.nih.gov/pubmed/29625932