There is no indication that caffeine, a natural component of both coffee and tea, is a risk factor in human cancer. All clinical studies to date suggest that caffeine consumption does not increase the risk of breast cancer. Researchers in a worldwide examination of 100,000 deaths due to breast cancer concluded that the data do not support an association between caffeine intake and the development of breast cancer. After reviewing the results of 17 studies, scientists reported in the Archives of Internal Medicine that coffee, tea and other caffeinated beverages do not cause any persistent increase in blood pressure. Some individuals sensitive to caffeine may experience a very small, short-lived rise in blood pressure, usually not lasting more than several hours.
Studies show any rise in blood pressure is less than that normally experienced when climbing stairs.
The bulk of scientific research does not support a link between caffeine consumption and cardiovascular disease. Finally, a recent review of studies on caffeine consumption of the equivalent of five to six cups of coffee a day did not increase the frequency or severity of cardiac arrhythmias. Three major studies involving more than 15,000 women have found no birth defects associated with caffeine consumption. Even offspring of the heaviest coffee drinkers were not found to be at higher risk of birth defects. Similarly, evidence from other human studies continues to support the conclusion that moderate consumption of caffeine by pregnant women does not predispose the mother to spontaneous abortion or preterm delivery, nor the fetus to low birth weight.