Being one of the most widely used stimulants in the world, caffeine causes the heart rate and blood pressure to increase, making the individual temporarily feel awake and energetic. Foods and beverages like coffee, teas, soft drinks, chocolate and cocoa are few of the most popular foods with caffeine. Caffeine acts as a stimulant on the central nervous system which cause the heart rate and blood pressure to increase. The caffeine can also be diuretic, causing the kidneys to excrete more urine.

However, too much intake of this substance can cause anxiety, jitters, inability to focus, irritability, insomnia. gastrointestinal unrest and nervousness. Much higher doses can even lead the risk to irregular heart beats increases and even miscarriage or slow growth of fetus in pregnant women. It can also lead to increased risk of osteoporosis and bone fracture in post menopausal women.

Caffeine acts as an ergogenic aid, affecting performance in exercise and sports. This ergogenic effect of caffeine can hardly be explained by researchers. Ingested caffeine is quickly absorbed in the body and peak in 1-2 hours and can increase endurance to well-trained athletes. Caffeine has a direct effect on muscle contraction during anaerobic exercise.

How come can caffeine improve endurance? It's because the muscle glycogen, which is the stored energy in the muscle tissue that is broken down during exercise, is spared. Glycogen sparing may occur as a result of caffeine's ability to increase fat availability for skeletal muscle use.

The researches also showed an improvement on the athletes' performance after caffeine intake, although many of the mechanisms to explain performance are unclear. There are still much research to do. And because caffeine enhances performance in many individuals, it has been banned by the International Olympic Committee.