Caffeine is a bitter, white crystalline xanthine alkaloid acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants. It is most commonly consumed by humans. In humans, caffeine acts as a central nervous system, temporarily causing alertness. It is the world's most widely consumed psychoactive drug containing caffeine. Beverages containing caffeine such as, coffee, tea and energy drinks has great popularity worldwide. Caffeine is toxic at sufficiently high doses, but ordinary consumption poses few known risks to health, even when carried on for years — there may actually be a modest protective effect against some diseases, including certain types of cancer. The effect of caffeine on sleep is highly variable across individuals. With heavy use, strong tolerance develops rapidly and caffeine can produce clinically significant physical and mental dependence.Caffeine increases the movement of free fatty acids in the blood. Caffeine has also been shown to decrease fatigue during low to moderate intensity exercise lasting over 2 hours. However, it increases the metabolic rate, heart rate and blood pressure. Rapid heart rate can occur leading to an unusually high heart rate during exercise. Longterm effects decrease as the body adjusts to the caffeine intake level. Caffeine may promote dehydration due to increased urination. Any level of dehydration can decrease energy levels up to 30%.
Short-term Effects
Caffeine taken in beverage form begins to reach all tissues of the body within five minutes. Peak blood levels are reached in about 30 minutes. Half of a given dose of caffeine is metabolized in about four hours, more rapidly in smokers and less rapidly in newborn infants, in women in late pregnancy, and in sufferers from liver disease. Almost all ingested caffeine is metabolized.
Ingestion of the amount of caffeine in one or two cups of coffee (75-150 mg) causes many mild physiological effects. General metabolism increases - expressed as an increase in activity or raised temperature, or both. The rate and breathing increases, as does urination and the levels of fatty acids in the blood and of gastric acid in the stomach. However, at least one other component of coffee also increases gastric acid secretion. Therefore ulcer sufferers may not achieve relief by switching to decaffeinated coffee.
Caffeine use may increase blood pressure:
Caffeine stimulates the brain and behavior. Use of 75-150 mg of caffeine elevates neural activity in many parts of the brain and enhances performance at simple intellectual tasks and at physical work that involves endurance but not fine motor coordination.
The effects of caffeine on sleep:
If taken before bedtime, it usually delays sleep onset, shortens overall sleep time, and reduces the depth of sleep. After using caffeine, sleepers move more during sleep, and report a reduction in the quality of sleep. Larger doses of caffeine, especially when given to non-users, can produce headache, abnormally rapid heartbeat and even delirium.
Tolerance and Dependence:
Tolerance refers to the body's "getting used" to a drug with its repeated taking. Researches has suggested that, with experience of the drug, the same dose produces a reduced effect and a larger dose is required to produce the same level of effect. Absence of caffeine also makes regular users feel irritable and tired. Relief from these withdrawal effects is often given as a reason for using caffeine.
Long-term Effects:
Long-term effects of a toxic nature do not appear evident when regular caffeine use is below about 650 mg a day. Above this level, users may suffer from chronic insomnia, persistent anxiety and depression, and stomach ulcers. Caffeine use appears to be associated with irregular heartbeat and it may raise cholesterol levels. Caffeine can cause changes in the cells of the body and in the way in which they reproduce themselves. Pregnant women have been advised to restrict caffeine.
Stimulant effects:
Caffeine is a cenral nervous system, metabolic stimulant,and is produces increased wakefulness, faster and clearer flow of thought, increased focus, and better general body coordination. The amount of caffeine necessary to produce effects varies from person to person, depending on body size and degree of tolerance. Caffeine has a number of effects on sleep, it improves performance during sleep deprivetion may lead to subsequent insomnia.
Physical effects:
Consumption of large amounts of caffeine can lead to a condition known as caffeinism. Caffeinism usually combines caffeine dependency a wide range of unpleasant physical and mental conditions including nervousness, irritability, restlessness, insomnia, and headaches caffeine use. There is evidence that caffeine consumption may protect against the development of Alzheimer's disease in later life. There is no evidence that coffee stunts a child's growth. Caffeine may increase the effectiveness of some medications including ones used to treat headaches.
Psychological:
In moderate doses it may reduce symptoms of depression and lower suicide risk. High doses may trigger anxiety and rarely mania and psychosis. Caffeine can have both positive and negative effects on anxiety disorders depending on the dose. At high doses, typically greater than 300 mg, it can both cause and worsen anxiety. At low doses it may reduce symptoms of anxiety. Caffeine withdrawal, on the other hand, can cause an increase in anxiety level. Moderate doses caffeine typically does not affect memory or learning. It does however improve cognitive function in people who are fatigued, due to its effect on alertness.
Sources:
http://lifehacker.com/5585217/what-caffeine-actually-does-to-your-brain
http://www.overcaffeinated.org/effects-of-caffeine-on-the-body.php
