Almost 200 years ago, a young German chemist named Friedrich Ferdinand Runge isolated a molecule from coffee beans; he named the substance kaffein. Today, scientists are still studying the properties of this bitter, white powder. More than sixty plants are known to produce caffeine, whose pungent taste helps protect them from insect predators.

Caffeine is probably the most widely used drug in the world. Humans have been consuming caffeine for hundreds of years, primarily in the form of coffee, tea and cocoa. Today, it is also added to soft drinks and energy drinks and is a component of some over-the-counter medications. Many of the world’s people, including children, ingest it in some form daily.

The body absorbs caffeine in less than an hour, and it remains in the system for only a few hours, passing from the gastrointestinal tract into the bloodstream within about ten minutes and circulating to other organs, including the brain. Caffeine molecules are small and soluble in fat, properties that allow them to pass through a protective shield known as the blood-brain barrier and directly target the central nervous system.

Caffeine acts on the body in many ways, some of them probably still unknown. However, caffeine accomplishes its principal action as a stimulant by inhibiting adenosine, a chemical that binds to receptors on nerve cells and slows down their activity. Caffeine binds to the same receptors, robbing adenosine of the ability to do its job and leaving caffeine free to stimulate nerve cells, which in turn release epinephrine (also known as adrenaline), a hormone that increases heart rate and blood pressure, supplies and energy boost, and in general makes people feel good.

For all its popularity, caffeine retains a somewhat negative image. It is, after all, a mildly habit-forming stimulant that has been linked to nervousness and anxiety and that causes insomnia. It affects most of the body’s major organs. Recent research casts doubt on the magnitude of many of these seemingly undesirable effects and even suggests that a daily dose of caffeine may reduce the risk of some chronic diseases, while providing short-term benefits as well.

Daily caffeine consumption has been associated with lowered incidence of type II diabetes, Parkinson’s disease, and Alzheimer’s disease. How caffeine works to thwart diabetes, a condition characterized by high levels of glucose in the blood, remains unknown, but glucose tolerance or more efficient glucose metabolism may be involved. Parkinson’s disease, a central nervous system disorder that causes tremor and joint stiffness, is linked to insufficient amounts of a substance called dopamine in the brain.

Caffeine may interact with brain cells that produce dopamine and help maintain a steady supply. The role of caffeine in Alzheimer’s disease, which damages the brain and causes memory loss and confusion, may be related to a problem in the blood-brain barrier, possibly a contributor in Alzheimer’s, if not the minor cause. Caffeine has been found to protect the barrier against disruption resulting from high levels of cholesterol.

Habitual coffee and tea drinkers had long been observed to have a lower incidence of non-melanoma skin cancers, although no one knew why. A recent study found that caffeine affects skin cells damaged by ultraviolet radiation, a main cause of skin cancer. Caffeine interferes with a protein that cancerous cells need to survive, leaving the damaged cells to die before they become cancerous. Drinking caffeinated coffee has also been associated with a decreased incidence of endometrial cancer – that is, cancer of the cells lining the uterus. The strongest effect appears to be in overweight women, who are at greatest risk for the disease. Researchers believe blood sugar, fat cells, and estrogen may play a role. Although the mechanism remains unknown, people who drink more than two cups of coffee or tea a day reportedly had about half the risk of developing chronic liver disease as those who drink less than one cup of coffee daily; caffeinated coffee has also been associated with lowered risk of cirrhosis and liver cancer.

While many of caffeine’s undesirable effects, such as elevated heart rate and blood pressure, are brief, some short-term benefits, including pain relief, increased alertness, and increased physical endurance, have also been attributed to caffeine. As a component of numerous over-the-counter diet pills and pain relievers, caffeine increases their effectiveness and helps the body absorb them more quickly. By constricting blood vessels in the brain, it can alleviate headaches – even migraines – and can help counter the drowsiness caused by antihistamines.

Caffeine does not alter the need for sleep, but it does offer a temporary solution to fatigue for people who need to stay alert. Research has shown that sleep-deprived individual who consumed caffeine had improved memory and reasoning abilities, at least in the short term.Studies of runners and cyclists have shown that caffeine can improve their stamina – hence its addition to energy boosting sports drinks.

People who consume a lot of caffeine regularly may develop temporary withdrawal symptoms, headache being the most common, if they quit or cut back on it abruptly. Fortunately, these symptoms last only a day or two in most cases. Individuals who are more sensitive to the stimulatory side effects of caffeine may want to avoid it, but most doctors agree that the equivalent of three cups of coffee a day does not harm healthy people. There is no medical basis to give up daily caffeine and many reasons to include a moderate amount in one’s diet.