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Effects of Caffeine on the Body


Updated April 09, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Caffeine is a Stimulant Drug

Caffeine is currently the world's most commonly used drug. And because caffeine is present in so many common foods and drinks, it is easy to forget that it is a drug. It is even an ingredient in beverages and foods that are marketed to kids.

Caffeine is a stimulant drug -- it may surprise you to realize that this is the same type of drug as cocaine and meth, substances we think of as hard drugs. Stimulant drugs work partly by stimulating the sympathetic nervous system, which causes the same physical effects as the "fight or flight response" -- speeding up the heart and breathing, making you feel more alert, and increasing muscle tension. And when caffeine is consumed in large quantities, the side effects can range from unpleasant to severe, sometimes even resulting in caffeine overdose.

Even when caffeine is consumed in moderation, there is evidence that there are longer-term negative physical effects. This article gives an overview of both the short-term and longer-term effects of caffeine on the body.

Effects of Caffeine on the Heart

In simple terms, the stimulant effect of caffeine speeds up the heart rate. Research shows that the level of caffeine at which the heart rate is significantly affected is 360 milligrams, the equivalent of about three and a half cups of brewed coffee.

For most people who drink caffeine in moderation, this isn't necessarily harmful -- but for people who are prone to anxiety, this may increase the likelihood of panic reactions, because caffeine also increases anxiety, and people experiencing panic reactions often worry they are having a heart attack.

In higher doses, caffeine can cause more significant effects on the heart by changing the speed and regularity of your heartbeat. This is known as tachycardia or cardiac arrythmia, and can be serious. If you think your heartbeat is abnormal, check with your doctor.

It is unclear at the moment whether caffeine increases the risk of cardiovascular problems in the longer term. Several studies have indicated no increased risk for cardiovascular problems in either men or women related to caffeine intake, but current recommendations are that people who already have heart problems should avoid caffeine, as other studies show that these conditions can be exacerbated by caffeine and other stimulants. This includes children with cardiovascular problems, who may be exposed to caffeine through soda and energy drinks.

Effects of Caffeine on Blood Pressure

Studies have conclusively shown that caffeine consumption raises blood pressure. This effect of caffeine, known as the "pressor effect," is evident across age and gender groups, and is particularly pronounced in people with hypertension (high blood pressure). If you are unsure of whether this applies to you, it is a simple process to have your blood pressure checked by your physician, and to get their advice on moderating your caffeine intake.

Effects of Caffeine on Bone Density

High coffee consumption has been linked to osteoporosis in men and women. Consumption of soft drinks in children is associated with lower bone mass, although this seems to be at least partially accounted for by those children who drink a lot of soft drinks also having a lower intake of milk. In older women, several studies have shown a link between high caffeine intake and lower bone density, while in younger women, this seems of particular concern when the women use progesterone-only contraceptives such as depot medroxyprogesterone acetate, or Depo Provera.


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Farag, N., Whitsett, T., McKey, ., Wilson, M., Vincent, A., Everson-Rose, S., & Lovallo, W. "Caffeine and Blood Pressure Response: Sex, Age, and Hormonal Status." Journal of Women's Health 19:1171-1176. 2010.

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Hammond, C., & Gold, M. "Caffeine Dependence, Withdrawal, Overdose and Treatment: A Review." Directions in Psychiatry 28:177-189. 2008.

El Maghraoui et al. "Risk factors of osteoporosis in healthy Moroccan men," BMC Musculoskeletal Disorders 11:148. 2010.

Libuda, L., Alexy, U., Remer, T., Stehle, P., Schoenau, E. & Kersting, M. "Association between long-term consumption of soft drinks and variables of bone modeling and remodeling in a sample of healthy German children and adolescents." The American Journal Of Clinical Nutrition 88: 1670-1677. 2008.

Seifert, S., Schaechter, E., Hershorin, E. & Lipshultz, S. "Health Effects of Energy Drinks on Children, Adolescents, and Young Adults." Pediatrics 127:511-528. 2011.

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