Tea leaves, coffee and cocoa beans, as well as kola nuts all contain caffeine. In 1987 the US Food and Drug Administration found no evidence that normal caffeine intake produced any increased risk to health. The American Medical Association came to a similar conclusion in relation to the health and safety of drinking coffee. Two studies in Norway and Hawaii found no relationship between coffee intake and cancer risk, confirming the stance of the American Cancer Society that there does not seem to be any relationship between caffeine and cancer. However, different individuals react differently to caffeine.
Caffeine can cause some individuals to have difficulty sleeping at night.
It can also cause some people to have fitful sleep, mood changes, heartburn, stomach upsets, or headaches. People who have a high caffeine intake may experience headaches or withdrawl symptoms if they suddenly cease getting their normal amount of caffeine. Because it is a stimulant, caffeinated beverages are not recommended for replacing body fluids lost while sweating in hot weather or hot work environments.