Should family physicians discourage, encourage, or ignore their patients' caffeine intake? After years of investigation and concern over caffeine's adverse effects, there is evidence that caffeine in moderate amounts is not harmful and may have some health benefits.
The most common sources of caffeine for adults are coffee, tea, and sodas. The serving size, the type of product ingested, and the preparation of the product determine the amount of caffeine consumed. An 8-oz serving of drip-brewed coffee contains an average of 85 mg of caffeine, compared with 40 mg in the same amount of brewed tea and 3 mg in decaffeinated coffee. The amount of caffeine in sodas ranges from 24 to 45 mg per 8-oz serving. The Wall Street Journal recently reported large variations in the caffeine content of commercially available coffee (86 to 124 mg per 12 oz).1 Most studies of caffeine are extrapolated from coffee consumption.
The major health concerns about caffeine are whether it is carcinogenic and what effects, if any, it has on the cardiovascular and reproductive systems. Lesser concerns include its potential physiologic and behavioral effects.
Caffeine does not cause or worsen cardiovascular disease.2 It also does not cause serious arrhythmias,3 hypertension,4,5 or coronary artery disease.6 The Joint National Commission for the Detection and Treatment of High Blood Pressure VII does not recommend restricting caffeine consumption to control high blood pressure.
Caffeine is not carcinogenic. It does not increase the risk of colon or breast cancers,7 but the data for stomach, liver, prostate, and lung cancers are limited. Most studies of its effects on bladder and pancreatic cancers found no increased risk8; in the few case-control studies that found an association between caffeine consumption and bladder or pancreatic cancers, the association was weakened when results were adjusted for cigarette smoking.9
Women can drink caffeine safely; it does not increase the risk of fibrocystic breast disease or symptomatic breast discomfort. Although some women may experience delayed conception with caffeine intake greater than 250 mg per day (i.e., the equivalent of three 8-oz cups of brewed coffee), the most detailed prospective study found no association between caffeine consumption and delayed conception.10
Pregnant women are not at greater risk of spontaneous abortion when their caffeine consumption is adjusted for the nausea associated with early pregnancy or when caffeine intake is less than 300 mg per day.11,12 Caffeine does not increase the risk of preterm delivery, genetic abnormalities, or reduction in intellectual functioning.
Caffeine intake is associated with an increase in urinary calcium excretion. However, caffeine intake of less than 400 mg per day has no effect on calcium balance,13,14 and studies that controlled for calcium intake did not find a correlation between caffeine consumption and reduced bone mineral density.15
Because caffeine is a methylxanthine with mild diuretic properties, it is commonly thought that caffeinated beverages are dehydrating. However, normal caffeine intake does not increase the risk of dehydration in athletes or nonathletes.16
Caffeine's effect on human behavior is difficult to determine because of the small size of many studies and numerous variables that can confound the results. Its effect on behavior seems to be the most individually dependent. In general, caffeine increases alertness in situations where arousal is low (e.g., in night-shift workers, in the early morning). Daytime vigilance is also increased. In large amounts, caffeine can increase the time required to fall asleep and reduce sleep duration. However, tolerance to this effect does occur in that regular consumers experience less sleep disturbance.17 Withdrawal symptoms may occur with abrupt discontinuation of caffeine.
What about caffeine's possible health benefits? Coffee drinking is associated with a reduced risk of developing type 2 diabetes, possibly by inducing weight loss. The risk of symptomatic gallstone disease in men, rheumatoid arthritis, alcoholic cirrhosis, and Parkinson's disease is also reduced.
Caffeine intake causes no long-term health consequences in adults and may confer some health benefits. Therefore, moderate caffeine intake is not contraindicated; patients may safely consume two to three cups of coffee or the equivalent amount of caffeine on a daily basis. Family physicians can devote their dietary counseling time to other issues.