Caffeine affects nearly every organ in the body. Caffeine may benefit certain organs and their functions, for example by helping reduce risk of liver disease or Alzheimer's disease. It may pose a risk to certain organs, for example by increasing risk of stomach ulcers or heart palpitations. The U.S. Food and Drug Administration says doctors recommend no more than 100 to 200 mg of caffeine per day, or the equivalent of one or two 5-oz. cups, although individual weight, physical condition and caffeine sensitivity are influencing factors. Speak with your doctor before increasing your intake of caffeine.
Brain
Caffeine stimulates the central nervous system, generally producing an immediate and temporary increase in alertness and a tendency toward either improved mood or anxiety. Numerous studies explore caffeine's potential benefits to neurocognitive health. In several studies, such as one published in "Journal of Alzheimer's Disease" in 2009, caffeine was found to reduce and reverse cognitive decline in mice with Alzheimer's disease. In the November 2010 "Annals of Neurology," caffeine was reported to improve brain development in premature infants. The FDA, however, classifies caffeine as a drug as well as a food additive, warning that its effects on the central nervous system may include nervousness, jitteriness, dizziness, headache and insomnia.
Heart
Caffeine increases heart rate and dilates blood vessels, thus raising blood pressure. It may also cause or exacerbate heart palpitations. Several studies, however, have linked caffeinated coffee with lowered risk of coronary heart disease and stroke. For example, a 2009 study in "Circulation" found that coffee consumption moderately reduced risk of stroke in women, and a 2010 study in "Arteriosclerosis, Thrombosis and Vascular Biology" found evidence supporting a link between moderate caffeinated coffee and tea consumption and reduced coronary heart disease risk.
Lungs
Caffeine relaxes the bronchial passages to and from the lungs, hence its use in treating asthma. In the May 2006 "New England Journal of Medicine," caffeine was found to be effective in helping premature infants with apnea, or the cessation of breathing, to restore breathing on their own. The researchers attributed this effect to caffeine's action of reducing the rate of enlargement of the lungs and bronchial passages common in infants with low birth weight.
Stomach and Intestines
Most of the caffeine you consume is absorbed into the bloodstream through the stomach and small intestine. Caffeine stimulates stomach acid secretion and can therefore lead to or exacerbate duodenal ulcers, upset stomach and heartburn.
Liver and Gallbladder
Most of the caffeine absorbed into the bloodstream is then metabolized in the liver. In such studies as a 2010 "Journal of Agriculture, Food and Chemistry" examination of caffeine's anti-diabetic effects in mice, caffeine helped improve several conditions of the liver, including fatty liver and hyperglycemia, in both cases helping reduce risk of Type 2 diabetes. A study reported in 2010 in the journal "Hepatology" linked caffeine consumption with reduced risk of liver disease. Caffeine stimulates gallbladder contractions and the secretion of bile. It also lowers the cholesterol content of bile. According to the University of Maryland Medical Center, studies mostly from the late 1980s have suggested that caffeine consumption in the form of coffee lowers risk of developing gallstones by stimulating bladder contractions and lowering biliary cholesterol levels, although caffeine from beverages like tea and cola did not provide the same benefits.
Bladder
Caffeine is a natural diuretic that stimulates the bladder and increases urination, as shown in a 2011 study in "Urology Annals" in which caffeine was found to promote early urinary frequency and urgency. In 2009, coffee and caffeine intake were linked to an increased risk of bladder cancer in Japanese adult male non-smokers or former smokers.
References
- U.S. Food and Drug Administration: Medicines in My Home: Caffeine and Your Body; 2007
- "Journal of Alzheimer's Disease"; Caffeine Suppresses Amyloid-beta Levels in Plasma and Brain of Alzheimer's Disease Transgenic Mice; C. Cao et al.; 2009
- "Annals of Neurology"; Caffeine and Brain Development in Very Preterm Infants; L.W. Doyle et al.; November 2010
- "Circulation"; Coffee Consumption and Risk of Stroke in Women; E. Lopez-Garcia et al.; March 2009
- "Arteriosclerosis, Thrombosis and Vascular Biology"; Tea and Coffee Consumption and Cardiovascular Mortality; J.M. de Koning Gans et al.; August 2010
- "New England Journal of Medicine"; Caffeine Therapy for Apnea of Prematurity; B. Schmidt et al.; May 2006
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