How harmful is caffeine?

Caffeine is a type of chemical, known as an alkaloid, which occurs in several kinds of plant. Biologists do not fully understand why plants such as coffee and tea make caffeine, but one theory is that it has evolved as a natural herbicide to help growing shrubs overcome competing plants.
The effects of caffeine vary. Women retain caffeine in their body for much longer when they are pregnant, where as smokers eliminate caffeine twice as quickly as non-smokers. 
 
The most noticeable effect is to stimulate the nervous system; people whop are sensitive to caffeine will certainly sleepless if they drink ordinary coffee before going to bed. However, the body can become habituated to caffeine and many regular coffee drinkers can take a cup or two in the evening without their sleep being disturbed.
 
Other physiological effects of caffeine include stimulating the production of urine and susceptible to irregular heart rhythms and palpitation find that these are triggered by caffeine.
 
Caffeine dose not accumulate in the body, so its effects are short-lived. But it has been accused at one time or another of contributing to most of the serious health problems of the 20th century, including heart disease, cancer and birth defects.