Caffeine

Caffeine is also known as mateine and its chemical name trimethylxanthine. Once consumed, caffeine boosts levels of epinephrine and norepinephrine, increasing vigilance, heart rate, blood pressure and fat oxidation and reducing sleepiness as a result.
There is currently no RDA for caffeine, but experts have stated that healthy adults can generally consume up to 400 milligrams, the amount in about four cups of coffee, safely.
Caffeine has been consumed around the world for thousands of years in coffee, tea and yerba mate, but it was first isolated by German chemist Friedrich Ferdinand in 1819.

Caffeine Deficiency

Because caffeine is not naturally present in the human body, no strict deficiency can exist. However, levels of the substance can vary after consumption, and a relative deficiency can occur after cessation of long-term use. Some individuals naturally have high levels of the enzymes that break down caffeine, which results in their levels of the substance decreasing rapidly after ingesting it.

Habitual use of caffeine results in physical dependency on its effects. If this habit is discontinued, many bodily functions, including blood pressure and energy, slow down as the body perceives what can be considered a deficiency. As cessation continues, the body returns to homeostasis sans caffeine.

Caffeine Excess

An excess of caffeine can result from overconsumption of the substance or reduced ability to metabolize it. If a person drinks too much coffee for his or her tolerance, for example, anxiety and other symptoms of caffeine excess may result.

Some individuals have unusually low levels of enzymes necessary to process caffeine in the body, resulting in abnormally prolonged effects and increased side effects, such as muscle tension and nervousness. Notably, individuals who experience the longest effects from caffeine have also been found to be more prone to cardiovascular side effects from long-term use of caffeinated products.