High doses of caffeine, typically doses above 300 milligrams, can produce restlessness, anxiousness, nervousness, excitement, flushed face, diuresis, gastrointestinal problems, and headache. Doses above 1,000 milligrams can produce rambling speech, muscle twitching, irregular heartbeat, rapid heartbeat, sleeping difficulties, ringing in the ears, motor disturbances, anxiety, vomiting, and convulsions. Adverse effects of high doses of caffeine have been referred to as caffeine intoxication, a condition recognized by the American Psychiatric Association. Extremely high doses of caffeine— between 5,000 and 10,000 mg—can produce convulsions and death.
Extremely high doses of caffeine, well above dietary amounts, have been shown to produce teratogenic effects (birth defects) in mammals. Although there is some evidence to the contrary, dietary doses of caffeine do not appear to affect the incidence of malformations or of low-birth-weight offspring. Although there has been some suggestion that caffeine consumption increases the incidence of benign fibrocystic disease and cancer of the pancreas, kidney, lower urinary tract, and breast, asso ciations have not been clearly established between caffeine intake and any of these conditions. Similarly, dietary caffeine has been associated with little, if any, increase in the incidence of heart disease.
Controversies continue over the medical risks of caffeine. Although research has not definitively resolved all the controversies, health-care professionals must make recommendations regarding safe and appropriate use of caffeine. In a recent survey of physician specialists, more than 65 percent recommended reductions in caffeine in patients with arrhythmias, palpitations, tachycardia, esophagitis/hiatal hernia, fibrocystic disease, or ulcers, as well as in patients who are pregnant.
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