The most commonly known sources of caffeine are coffee and cocoa beans, cola nuts, and tea leaves. Caffeine is a pharmocologically active substance, yet the effects of caffeine are temporary and usually pass with several hours. The average caffeine consumption is 200 mg per day, and the top ten percent of Americans consume an average of 400 mg per day. With regular use, tolerance develops to many of the effects of caffeine. For example, a regular coffee drinker may not notice the effects of caffeine after several cups of coffee, yet the non-coffee drinker may feel nervous and jittery after only one serving of coffee.
Caffeine is one of the most thoroughly studied ingredients in the food supply.
Extensive research has not linked moderate caffeine consumption to any health risks, including cancer, heart disease, high blood pressure, or birth defects. Although many women report decreased symptoms of benign fibrous lumps in the breast, a 1986 study involving 3,000 women showed no association between caffeine intake and benign tumors, fibrocystic breast disease, or breast tenderness. Ulcer patients may not be so lucky, however. Caffeine can be hard on your bones. The more coffee a woman drinks, the more calcium is excreted in her urine suggesting caffeine is a risk factor for osteoporosis.