Caffeine is an active ingredient in many of the world’s most popular beverages – including coffee, tea and a wide range energy drinks and sodas-as well as in chocolate and certain other foods. Much of this substance’s popularity stems from its ability to stimulate the central nervous system, which includes your brain and spinal cord. While most people don’t often think of their favorite foods and drinks in chemical terms, caffeine’s ability to alter normal nervous system function technically qualifies it as a type of drug. As with other drugs, excessive use of caffeine can potentially harm your health in a number of ways.
Caffeine occurs naturally in portions of a variety of plants, including the beans of several different species of coffee plants; the buds and leaves of the tea species Camelia sinensis; the seeds of two different species of cola (or kola) plants; the seeds of the cocoa-bearing species Theobroma cacao; and the seeds of the Brazilian guarana plant (Paulinia cupana). It is also frequently produced synthetically by a number of food and beverage companies. Chemically, caffeine is a member of a group of substances known as xanthines; it has a relatively complex chemical structure, and scientists refer to it by several different names, including 1,3,7-trimethylxanthine and 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6,-dione.
Caffeine has a structural resemblance to a naturally occurring substance in your brain called adenosine, which also belongs to the xanthine chemical group. Under normal circumstances, adenosine plays a vital role in your central nervous system by regulating various aspects of your natural sleep cycle and making you drowsy if you’ve been awake for a long period of time. Like a variety of other naturally occurring substances, known collectively as neurotransmitters, adenosine achieves its effects by relaying specific chemical messages from nerve cell to nerve cell inside your brain. These nerve cells, or neurons, accept messages from adenosine and other neurotransmitters at specialized sites on their surfaces called receptors.
When caffeine enters your bloodstream, it travels to your brain; there, its structural resemblance to adenosine gives it the ability to block or disrupt adenosine’s access to the receptors on large numbers of neurons. In turn, this disruption delays the normal drowsiness that occurs when adenosine builds up over time at receptor sites. The overall effects of this process also include increases in your general alertness, increases in your ability to focus and concentrate, and decreases in your normal sensitivity to the presence of physical fatigue. It usually takes anywhere from five to 30 minutes for caffeine’s stimulating effects to kick in; residual effects of the chemical can linger for as long as 12 hours. Many people rely on the drug effects of caffeine as part of their normal daily routines.
Most caffeine users have a moderate daily intake of 200 to 300 milligrams, roughly the same as the average caffeine content of two to four eight-ounce cups of coffee. This level of intake is essentially harmless to most adults, according to the Mayo Clinic. However, some people have unusual sensitivities to this amount of caffeine and develop uncomfortable side effects such as restlessness, rapid heartbeat, insomnia, nervousness, stomach distress or abnormal irritability. Most people only risk the development of these problems when they raise their daily intake to 500 or 600 milligrams or more per day. In addition to your level of regular intake, factors that can alter your degree of caffeine sensitivity include your age, your weight, the presence of any anxiety-related health problems, and the amount and type of medications you normally take. Generally speaking, men appear to be more sensitive to caffeine than women.
People who use caffeine to avoid sleeping can potentially damage their long-term sleep cycles. This problem most commonly begins when daytime caffeine intake interferes with the user’s ability to sleep at night and, in response, the user consumes more caffeine the following day in order to stay awake. Over time, this pattern of usage can lead to sleep deprivation and cumulative sleep deficits that have increasingly negative effects on daytime alertness and general function.
Regular consumption of caffeine can also lead to a minor dependence on its central nervous system effects. Dependence means that your body needs a drug in order to feel “normal,” and that absence of that drug will lead to some form of withdrawal. Symptoms of caffeine withdrawal typically appear within a day after usage is suspended, and can include headaches, muscle pain, sweating, fatigue and feelings of unusual anxiousness. These symptoms generally ease a day or two after they begin.