Caffeine can be found in coffee, tea, cocoa and soft drinks. As a stimulant, it boosts alertness levels and energy production. For this purpose, it commonly is seen as a necessity for fast-paced modern life. In the short term, caffeine can have positive effects, but overconsumption or regular consumption over a long period of time can have profound negative effects on the body.
Caffeine enters the bloodstream through the stomach lining. It blocks adenosine, a neurotransmitter that calms the body and nerves in preparation for sleep. Instead, the body secretes adrenaline or epinephrine. The secretion of adrenaline into the bloodstream provokes the "fight or flight" response. Alertness and energy levels rise as a result. Dopamine production in the brain also increases, leading to feelings of happiness--the often-reported "caffeine high." According to the website Body Building 4 You, caffeine also increases muscular endurance by stimulating the release of calcium into the muscle cells. Calcium causes the electrochemical signals created by the brain and nervous system to pass through the muscles more efficiently, increasing strength and endurance in muscle exertion.
According to Southern Australia's Children, Youth and Women Health Services, long-term harmful effects of caffeine will occur in an average person if daily consumption exceeds 600 mg--approximately three cups of coffee or 10 cups of tea. Some long term health effects of caffeine include ulcers, cardiac stress and chronic insomnia. Caffeine causes ulcers because of increased stomach acid production. This acid wears through the mucous membrane that protects the stomach and esophagus from acid erosion. A constant state of adrenaline keeps the heart working. With little time to recuperate, the cardiac muscle begins to wear down more quickly from a constant influx of caffeine.
Different amounts of caffeine have varying effects on the human body. Metabolism, body size and frequency of use contribute to the effects caffeine will have. Someone with a high metabolism will process the caffeine quickly through the body so its effects will last a shorter time. Height and weight play a factor--the larger a person is, the more caffeine they have to consume to reach effective concentrations within the bloodstream. If someone uses caffeine regularly, her body will build up a tolerance to it over time. Therefore, the amount of caffeine needed to bring about its effects increases.