Nutrition & Health Info Sheets contain up-to-date information about nutrition, health, and food. They are provided in two different formats for consumer and professional users. These resources are produced by Dr. Rachel Scherr and her research staff. Produced by Elisa Gonzalez-Smith, Ione Yu, Philena Nguyen, Rosie Ou, Britt Robinson, Anna M. Jones, and Rachel E. Scherr.
What is caffeine?
Caffeine is a chemical stimulant that nearly 90% of American adults consume every day.  This bitter substance is found naturally in the leaves and seeds of some South American and Asian plants. [1-3] However, caffeine is also added to other products, like energy drinks and medications. [1, 3] Coffee is the most commonly consumed caffeinated beverage worldwide. 
What are common dietary sources of caffeine?
Some natural sources of caffeine include coffee beans, tea leaves, kola nuts, and cacao (chocolate). Synthetic caffeine (which is produced in a lab) is sometimes added to energy drinks, medications, soft drinks, gum, and snacks [1, 3].
Caffeine is most commonly consumed in drinks which can contain a wide range of caffeine. An 8 ounce cup of coffee may contain anywhere from 95-200mg of caffeine, while an 8 ounce cup of tea may contain 14-60mg of caffeine. 
How much caffeine is safe to consume?
Caffeine can be safely consumed by most adults at levels of around 400 mg per day, or approximately four cups of brewed coffee. This does not take into account that certain people are more sensitive to caffeine than others. [3, 4] Consuming too much caffeine can lead to certain side effects, such as:
- Restlessness and shakiness
- Rapid or abnormal heart rhythm
- Dependency, where an individual needs to intake more caffeine to get the same results of caffeine they usually would feel 
The effects of caffeine should be limited in certain groups of people, such as:
- Pregnant or breastfeeding women
- Individuals with sleeping disorders
- Individuals with migraines or chronic headaches
- Individuals with anxiety
- Individuals with ulcers or acid reflux
- Individuals with fast or irregular heart rhythms
- Individuals with or had high blood pressure
- Children and teenagers
- Individuals taking certain supplements or medications 
What are the effects of caffeine supplementation on health?
Caffeine can affect the nervous system, metabolism, and the ability to sleep. Caffeine levels in blood are highest during the first hour of consumption and its effects can last up to six hours. 
- Neurological effects: Caffeine stimulates the central nervous system and consumers can feel energized by it.  Some studies have demonstrated some positive effects of caffeine consumption on the brain. One study found that 200 mg of caffeine per day may improve long-term memory. According to other reports, caffeine may also be valuable in treating some kinds of headaches. [3, 6]
In children, caffeine consumption can affect the reward-and-addiction center. These results may differ by gender and can affect food and drink preferences later in life, and caffeine consumption is not recommended for children. [6,7]
- Metabolic effects: The stimulating effect of caffeine to the body’s central nervous system may cause feelings of alertness or agitation, increased blood pressure, and more frequent urination.  It can also increase the amount of stomach acid that is released and cause heartburn. It can also interfere with the body’s ability to absorb calcium from food and supplements. 
- Sleep effects: Restricted sleep studies suggest that gum that contains caffeine may increase both response- and event-detection speed and be beneficial for cognitive function in general.  Results varied between individuals that were sleep deprived and caffeine might hinder sleeping while it is active in the blood. 
What are the effects of cutting back on caffeine?
Suddenly cutting out caffeine after routine consumption may cause caffeine withdrawal.
Symptoms of caffeine withdrawal include headaches, drowsiness, irritability, nausea, and difficulty concentrating. [1-3] Slowly cutting down intake of caffeine over time can help limit these symptoms. [5, 6]
Does caffeine improve physical performance?
Research on caffeine’s effect on physical performance has been inconsistent. Caffeine consumption has been shown to reduce triathlon swim time and allow for faster completion of triathlons.  It has also been shown to slightly enhance race performance and increase performance in basketball players. [11, 12] However, caffeine consumption was not shown to increase jump height, non-treadmill sprint speeds, or cardiovascular fitness. [12, 13]
- Frary C, Johnson R, Wang M. Food sources and intakes of caffeine in the diets of persons in the United States. J Am Diet Assoc. 2005;105(1):110-113. doi:10.1016/j.jada.2004.10.027
- Caffeine: MedlinePlus. MedlinePlus Trusted Health Information for You. https://medlineplus.gov/caffeine.html. Accessed March 14, 2017.
- Caffeine: How much is too much? Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/caffeine/art-20045678. Published March 8, 2017. Accessed March 17, 2019.
- Angelucci M, Cesário C, Hiroi R, Rosalen P, Cunha CD. Effects of caffeine on learning and memory in rats tested in the Morris water maze. Brazilian Journal of Medical and Biological Research. 2002;35(10):1201-1208. doi:10.1590/s0100-879x2002001000013.
- Shapiro RE. Caffeine and headaches. Current Pain Headache Reports. 2008;12(4):311-315.
- Seifert SM, Schaechter JL, Hoershorin ER, Lipshultz SE. Health Effects of Energy Drinks on Children, Adolescents, and Young Adults. Pediatrics. 2011;127(3):511-528. doi:10.1542/peds.2009-3592.
- Spilling the Beans: How Much Caffeine is Too Much?. U.S. Food and Drug Administration. https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much. Published 2019. Accessed September 26, 2019.
- Kamimori GH, Mclellan TM, Tate CM, Voss DM, Niro P, Lieberman HR. Caffeine improves reaction time, vigilance and logical reasoning during extended periods with restricted opportunities for sleep. Psychopharmacology. 2014;232(12):2031-2042. doi:10.1007/s00213-014-3834-5.
- Griffin M. Arabica and Robusta Coffee Plant. Coffee Research. http://www.coffeeresearch.org/agriculture/coffeeplant.htm. Accessed March 14, 2017.
- Potgieter S, Wright HH, Smith C. Caffeine Improves Triathlon Performance: A Field Study in Males and Females. International Journal of Sport Nutrition and Exercise Metabolism. 2018:1-34. doi:10.1123/ ijsnem.2017-0165.
- Clarke ND, Richardson DL, Thie J, Taylor R. Coffee Ingestion Enhances One-Mile Running Race Performance. International Journal of Sports Physiology and Performance. 2017:1-20. doi:10.1123/ ijspp.2017-0456
- Puente C, Abián-Vicén J, Salinero J, Lara B, Areces F, Coso JD. Caffeine Improves Basketball Performance in Experienced Basketball Players. Nutrients. 2017;9(9):1033. doi:10.3390/nu9091033.
- Hahn CJ, Jagim AR, Camic CL, Andre MJ. The acute effects of a caffeine-containing supplement on anaerobic power and subjective measurements of fatigue in recreationally-active males. Journal of Strength and Conditioning Research. 2018:1. doi:10.1519/jsc.0000000000002442.
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