Caffeine, known chemically as 1,3,7 trimethylxanthine, is a bitter substance found in coffee beans, tea leaves, cacao pods and kola nuts. It is one of the most common stimulants in the world, and achieves its main effects by making certain changes in your central nervous system. It also produces changes in other systems throughout your body.
Caffeine Absorption
When you consume caffeine, roughly 99 percent of it passes from your small intestine to your bloodstream in about 45 minutes, and the effects of the chemical can start to take hold in as little as 15 minutes. Unlike some other substances, caffeine can easily pass through the blood-brain barrier and enter the bloodstream in your central nervous system, as well as your cerebrospinal fluid. It can also pass through the placental barrier and enter the bloodstream of a developing fetus. Because of certain details in its chemical construction, caffeine can pass through cellular membranes throughout your body.
Central Nervous System Stimulation
Inside your brain, caffeine competes with a chemical called adenosine, which acts as a neurotransmitter and relays certain signals inside your nervous system. Normally, adenosine levels build up in your body while you're awake and trigger a gradual drowsiness that eventually makes you want to sleep. By stopping adenosine from activating receptors on your nerve cells, caffeine inhibits its effects, disrupts sleep signaling and causes central nervous system stimulation. The metabolism of caffeine inside your body produces two other chemicals, called theophylline and paraxanthine, which also have stimulating effects.
Additional Effects
In addition to its stimulating effects, caffeine affects your body by increasing your urine output, constricting your blood vessels, increasing your heart rate and relaxing your airways. It can also trigger significant short-term increases in your blood pressure. No one knows precisely why this blood pressure-related effect occurs, according to MayoClinic.com, although it may be a result of caffeine's blood vessel-constricting effects or its alteration of normal function in your adrenal glands. If you regularly consume large amounts of caffeine, it may also eventually lower your bone density by interfering with your body's absorption and use of the mineral calcium.
Dependence and Side Effects
If you regularly consume caffeine, your body can potentially develop a dependence on its presence. Possible consequences of this dependence include withdrawal symptoms such as headaches, nausea, vomiting, irritability and drowsiness. Avoid withdrawal symptoms by gradually decreasing caffeine use rather than stopping abruptly. If you consume more caffeine per day than is found in approximately four cups of coffee, you can develop side effects that include nervousness, muscle tremors, a rapid heartbeat, restlessness, insomnia, irritability and an upset stomach. Consult your doctor for more information on the ways in which caffeine can affect you.
References
- University of Washington: Caffeine
- Biology Online: Caffeine
- MayoClinic.com; Caffeine; How Does It Affect Blood Pressure?; Sheldon G. Sheps, M.D.; November 14, 2009
- MedlinePlus: Caffeine in the Diet
- MayoClinic.com: Caffeine; How Much Is Too Much? (Page 1); March 9, 2011
- Biology Online: Consumption and Metabolism of Caffeine
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