Caffeine is classified as a central nervous system stimulant. Ingested in moderate doses, caffeine can increase alertness; it also can increase the amount of time it takes to fall asleep, cause headaches and nervousness, and reduce fine motor coordination.
Caffeine enters the bloodstream via the stomach and small intestine. Its effects can begin as quickly as 15 minutes after it is ingested. Caffeine stays in the body for hours – only about half of the caffeine is eliminated in the first 6 hours.
Some studies show that caffeine can cause a physical dependence if someone takes the equivalent of four or more cups of coffee per day. One way to tell if there is a physical dependence is if someone feels the “need” for caffeine, and has withdrawal symptoms such as headache, fatigue and muscle pain 24 (or more) hours after their last cup of coffee or bottle of coke.
Caffeine can also be fatal to those who overdose to the extreme. Medical literature contains several reports of people who died after submitting to unorthodox practices such as caffeine injections or coffee enemas. However, the lethal caffeine level is very high – more than 10 grams, or the equivalent of 80 to 100 cups of coffee at one sitting.
During the past 40 years, a number of studies have been conducted to determine whether there is any link between coffee consumption and cardiovascular disease. To date, the weight of scientific evidence has established no causal link between coffee consumption and cardiovascular disease. The lack of a causal relationship is strongly supported by well-controlled, prospective studies, including the extensive Framingham Heart Study.
Heart Attack. Among the participants of the Framingham Heart Study were 717 people who began the study with some type of cardiac disease. Over the course of the study investigators tracked these individuals' cardiovascular health, including occurrence of heart attack, and then analyzed risk factors that led to recurrence. They concluded that there was no association between coffee intake and recurring heart attack episodes.
High Blood Pressure. In 1990, researchers at the University of Tennessee concluded that moderate daily consumption of coffee does not elevate blood pressure. Many studies show that any change in blood pressure on first drinking coffee is minimal. There is no strong evidence that caffeine intake increases the risk of being classified or treated for sustained hypertension.
Arrhythmias. Irregular heartbeats are experienced as "skipped," "flutters," or "palpitations." There is little evidence that caffeine can induce such arrhythmic episodes. In 1987, research published in the American Journal of Cardiology concluded, "caffeine does not increase the frequency or severity of ventricular arrhythmias." A 1990 study also concurs with these findings.
Cholesterol Levels. Most studies involving U.S. style filter-brewed coffee have not found an association between caffeinated or decaffeinated filtered coffee and increased risk of cholesterol-related heart disease. The best evidence to date shows neither caffeinated nor decaffeinated coffee consumption contributes significantly to the risk of heart disease or estimated risk based on serum cholesterol levels.
Sleeplessness. For most adults who have been caffeine-free for about 24-hours, a 200 mg dose of the stimulant - approximately the amount contained in two cups of coffee - can fight off fatigue. It can also extend the time necessary to pass through the early stages of slumber into deep sleep. Given caffeine's long half-life, if you drink several cups of coffee to ward off midday sleepiness, you may find yourself awake at 10 p.m.
Caffeine Addiction. It is possible to become habituated to caffeine. The Diagnostic and Statistical Manual of Mental Disorders IV describes caffeine-induced anxiety as characterized by rambling speech and thought and periods of inexhaustability. It notes that caffeine intoxication can be mistaken for manic episodes or panic attacks.
Caffeine can also be fatal to those who overdose to the extreme. Medical literature contains several reports of people who died after submitting to unorthodox practices such as caffeine injections or coffee enemas. However, the lethal caffeine level is the equivalent of oer 80 cups of coffee.