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Caffeine: A User's Guide

Nancy Clark, MS, RD


Waking up to a steaming mug of coffee, enjoying an iced tea with lunch, and drinking a cold cola for an afternoon pick-me-up are daily pleasures enjoyed worldwide. And because the mild stimulant effect of caffeine lasts only a few hours, people in need of a lift often seek out serving after serving of these caffeinated beverages.

Caffeine, however, has been condemned by "clean living" advocates because it has no nutritional value, is not needed for any physiologic function, and is commonly abused by the tired and stressed. As a result, many coffee drinkers worry that their early morning mugful will contribute to health problems. The truth is, coffee and other caffeinated beverages in moderation are not health demons.

Caffeine and Your Health

Caffeine is one of the best-researched substances in the food supply. The overwhelming scientific evidence suggests that, in moderation, it has no adverse health effects. According to the International Food Information Council, moderation means 1 to 2 mugs (10 to 20 ounces) of brewed coffee per day, or 3 to 6 12-ounce glasses of iced tea (table 1: not shown).

While little harm can be directly associated with coffee or other caffeinated beverages, coffee drinkers do tend to do things that contribute to health risks. Surveys suggest that they are more likely to smoke cigarettes, exercise too little, and eat fatty meats. Tea drinkers, in comparison, tend to exercise more and eat more fresh fruit.

For women, caffeine has been suspected as a factor in fibrocystic breast disease. But no research supports the connection, and the American Medical Association has stated that there is no association between caffeine intake and fibrocystic breast disease, benign tumors, breast tenderness, or breast cancer—or cancer of any type. Also, caffeine is not an important risk factor for osteoporosis in women who drink at least one glass of milk per day. But when caffeinated beverages replace milk, low calcium intakes may interfere with bone health.

A woman who wants to start a family should be aware that consuming over 300 milligrams of caffeine a day might increase the time it takes to get pregnant, as well as the risk of miscarriage or a low-birth-weight baby. The US Food and Drug Administration recommends that pregnant women avoid caffeine-containing foods and drugs or consume them only sparingly, because caffeine crosses the placenta and is a stimulant to the unborn baby. It is also transferred into breast milk, so women who breastfeed should avoid caffeine.

If you are prone to anemia, note that polyphenols in coffee and tea can interfere with iron absorption. Your best bet is to drink caffeinated beverages an hour before a meal, rather than afterward.

Some people become dependent on caffeine, experiencing withdrawal symptoms such as headaches, fatigue, or drowsiness if they abstain. These effects last only a few days and can be avoided by gradually reducing caffeine intake instead of quitting "cold turkey."

Energy-Enhancing Properties

Because caffeine enhances performance in many individuals, it has been banned by the International Olympic Committee. But ironically, the level at which caffeine is banned far exceeds the amount needed to enhance performance. Higher, illegal levels are generally attained with caffeine supplements, since a 150-pound athlete would need to drink 3 to 4 large cups of coffee within an hour before activity to reach the upper acceptable limit. Just 1.5 to 3 milligrams of caffeine per pound of body weight (225 to 450 milligrams for a 150-pound man) is enough for an energy-enhancing effect. That's as little as one 10-ounce cup of coffee!

Habitual caffeine consumers experience less ergogenic effect than people who consume it rarely. For the optimal ergogenic benefit, the trick may be to use caffeine strategically at certain points to allow for harder training, and then discontinue it to avoid developing a tolerance.

Caffeine affects each person's performance differently. Some athletes thrive on it; others prefer to abstain because it causes stomach upset, nervousness, or jitters. Clearly, if caffeine makes you queasy or lightheaded during exercise, don't use it!

Caffeine and Hydration

Caffeine also has a diuretic effect—that is, it enhances urine formation, often causing a need to urinate within an hour after consumption. Yet two studies with subjects who took caffeine before they exercised (1,2) showed no detrimental effects on hydration during exercise. Thus it appears that caffeine does not increase urine production during exercise. The extra adrenaline your body secretes during exercise may block caffeine's effect on the kidneys (3). However, responses to caffeine vary, so you should base your preexercise consumption on how caffeine affects your body.

After exercise, caffeine is a poor choice for fluid replacement. The safest bet is to tank up on noncaffeineated beverages just after activity, and then later, if you so desire, enjoy your favorite caffeinated beverage in moderation.


  1. Falk B, Burstein R, Rosenbloom J, et al: Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise. Can J Physiol Pharmacol 1990;68(7):889-892
  2. Gordon NF, Myburgh JL, Kruger PE, et al: Effects of caffeine ingestion on thermoregulatory and myocardial function during endurance performance. S Afr Med J 1982;62(18):644-647
  3. Graham TE, Spriet LL: Caffeine and exercise performance. Sports Science Exchange (Gatorade Sports Science Institute) 1996;9(1)

Remember: You, your physician, and your nutritionist need to work together to discuss nutrition concerns. The above information is not intended as a substitute for appropriate medical treatment.

Ms Clark is director of Nutrition Services at SportsMedicine Brookline in the Boston area. She is a fellow of the American College of Sports Medicine, a fellow of the American Dietetic Association, and a member of its practice group, Sports and Cardiovascular Nutritionists (SCAN).




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