Caffeine is the most widely used mild central nervous system stimulant, naturally present in many foods, including coffee, tea and cacao, among others. Coffee and tea remain the chief sources of caffeine in the U.S. diet; Coffee and brewed tea contain approximately 65-125 and 20-90 mg of caffeine per 8 oz. serving (1). However, energy beverages and caffeine-containing dietary supplements have been on the rise in the general population but more notably among athletes and active individuals.
Performance benefits attributed to caffeine include physical endurance, reduction of fatigue, and enhancing mental alertness and concentration (2). Many studies confirm caffeine’s ability to enhance mood and alertness (3), exercise performance (4), the speed at which information is processed, awareness, attention, and reaction time (5). At safe levels, caffeine through its wide-ranging physiological and psychological effects increases endurance in well-trained athletes. Abstaining from caffeine at least 7 days before use will give the greatest chance of optimizing the stimulant effect (6).
Perhaps no substance has been the subject of more conflicting scientific reports in recent years. For healthy adults, FDA has cited 400 mg/d as an amount not generally associated with dangerous, negative effects (7). Currently there are more than 25 published reviews supporting the safety of caffeine; the weight of evidence does not support a positive relationship between caffeine consumption and adverse effects, including reproductive or cardiovascular events in healthy individuals consuming at levels under 300 – 400 mg per day (8). Individuals with impaired vascular and/or cerebrovascular function should talk with a medical professional about their caffeine intake. Caffeine may act as a gastrointestinal irritant for those with gastritis, esophagitis, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), ulcerative colitis, Crohn’s Disease, and/or other related disorders. It can also increase urinary calcium if you consistently consume large quantities above 300 mg per day; this weakens your bone structure.
- International Food Information Council. Fact sheet: caffeine and health. Available at: http://www.foodinsight.org/Resources/Detail.aspx?topic=Fact_Sheet_Caffeine_and_Health. Accessed August 1, 2013.
- Heckman MA, Weil J, De Mejia EG. Caffeine (1, 3, 7-trimethylxanthine) in foods: A comprehensive review on consumption, functionality, safety, and regulatory matters. J Food Sci. 2010;75(3):R77-R87.
- Lorist M, Tops MM. 2003. Caffeine, fatigue and cognition. Brain Cogn 53:82–94.
- Doherty M, Smith PM. Effects of caffeine ingestion on exercise testing: a meta-analysis. Intn J Sport Nutr Exerc Metab 2004;14:626–46.
- Cysneiros RM, Farkas D, Harmatz JS, Von Moltke LL, Greenblatt DJ. Pharmacokinetic and pharmacodynamic interactions between zolpidem and caffeine. Clin Pharmacol Ther 2007;82:54–62.
- Ganio MS, Klau JF, Casa DJ, Armstrong LE, Maresh CM. Effect of caffeine on sport-specific endurance performance: A systematic review. J Strength Cond Res. 2009;23(1):315-324.
- U.S. Food and Drug Administration. For consumers: FDA to investigate added caffeine. Accessed on July 30, 2013. Available at: http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm350570.htm
- Peck JD, Leviton A, Cowan LD. A review of the epidemiologic evidence concerning the reproductive health effects of caffeine consumption: a 2000-2009 update. Food Chem Toxicol. 2010;48(10):2549-76.