Most of us consume caffeine in large doses daily, but little of us know about its effects, other than it giving us a lift when we are not feeling quite so energetic, so what specifically is it and what does it do. Caffeine (1,3,7-trimethylxanthine) (methyltheobromine) is a stimulant belonging to a chemical group known as alkaloids. Specifically, it is a methylated xanthine alkaloid, and is structurally and functionally similar to other chemicals in the group such as theobromine and paraxanthine, and is known to increase alertness and energy. It occurs naturally in the normal diet in plant foods like cola, coffee, tea, cocoa. It is absorbed rapidly following ingestion and has a half-life of 150-270mins, and maximises in effectiveness at around 15-60mins following ingestion. It works by inhibiting adenosine A1 and A2A receptors in the brain, which reduce activity of the central nervous system, by slowing down firing of neurons. Through this inhibition of adenosine, caffeine increases the neurotransmission of dopamine and choline, which increases feelings of alertness. It also acts as a diuretic by reducing the reabsorption of water by the kidneys. It also works as a potent fat burner by increasing the release of fat cells to be used as energy. Moreover, this effect is amplified during low carbohydrate diets. In addition to increasing mental alertness it, in exercise, caffeine is also known to increase motor activity, meaning that caffeine may improve the control of muscle contractions during exercise. Given the increase in alertness, energy and muscle contractions, caffeine is of particular interest to elite athletes, as these factors may permit increased productivity. However individual response to caffeine varies and it is subject to down-regulation effects, like most stimulants. Therefore cycling caffeine is beneficial, in order to maintain the same benefits over time. If you are interested in conferring these effects, the intake for caffeine is 3mg/kg (bodyweight) 15-60min prior to physical activity for exercise. Less specifically, 100-200mg between meals has been shown as an effective intake for weight management , and 200-400mg one hour before activity for improved physical performance. Remember though that there are no additional benefits from taking higher intakes (approximately 400mg), and that higher intakes of caffeine have been associated with increased heart rate, dizziness, jitters, anxiety, and impaired physical performance.