Caffeine is the reason that many people just can't function in the morning until they've had that first cup of coffee. It's a mild stimulant that occurs naturally in coffee and cocoa beans, tea leaves, and kola nuts (the basic ingredient in colas). While long-term, heavy coffee drinking has been shown not to harm the heart, too much caffeine can goose your heart rate and make you anxious for a few hours until the drug has had a chance to work its way out of your system. Though people who take caffeine regularly are generally less sensitive to its effects and it won't sober you up if you've been drinking, this buzz may keep you awake at night. Caffeine also stimulates the flow of stomach acid, so avoid it if you're susceptible to ulcers.

Experts disagree, but many studies show that caffeine junkies do experience withdrawal symptoms, including headaches , drowsiness, and a lack of concentration, when they miss their fix. Kids can get hooked, too. One study found that 8- to 12-year-olds who had been getting the equivalent of three cans of cola a day had shorter attention spans for a week when their caffeine supply was taken away. Cutting back gradually can help you avoid symptoms.

On average, a 5-ounce cup of drip-brewed coffee contains about 115 milligrams of caffeine. Instant kinds provide only half as much. A typical cup of brewed tea contains about 40 mg, although some brands can have as much as coffee. A can of soda contains around 35 mg, a mug of cocoa only 5 mg. A 1-ounce square of milk chocolate also averages 5 mg, but dark packs 20 mg. Many medications, including some pain relievers, cold and allergy remedies, and appetite-control pills, contain caffeine as well. One Excedrin has 65 mg; one NoDoz has 200 mg.

Each cup of coffee you drink steals a little bit of calcium from your bones -- about the amount you'd get from a teaspoon of milk. That's not a problem for café au lait fans, but it could be worrisome for postmenopausal women who drink their coffee black and don't get enough calcium. One study showed an acceleration in bone loss among older women who drank as little as two or three cups of coffee a day, compared with those who drank less or none at all. On the other hand, caffeine consumption had no effect on women who got more than 800 mg of calcium a day.

Moms-to-be and nursing mothers should go easy on caffeine. You may be more sensitive to its effects, and you can pass the drug on to your baby through the placenta or through breast milk. A Danish study of more than 86,000 pregnant women showed that unusually high coffee consumption led to a greater risk of complications. Researchers found that compared to the women who didn’t drink coffee, the risk of fetal death doubled among women who drank eight or more cups of coffee per day.

While a few studies have shown that taking 200 to 400 mg of caffeine just before exercise can increase endurance, there is more evidence to suggest that taking caffeine raises blood pressure and can be dangerous when combined with exercise. Many herbal "energy boosters," for example, combine caffeine with other stimulants like ephedra (now banned in all states) that have contributed to the deaths of famous athletes like Baltimore Orioles pitcher Steve Bechler. Keep in mind also that caffeine causes your body to lose water more quickly, so you should be careful to drink plenty of noncaffeinated drinks while working out.

Further Resources

Roberta Larson Duyuff, MS, RD, CFCS, The American Dietetic Association's Complete Food &Nutrition Guide. Chronimed Publishing, 1996, 1998.

References

First published January 5, 1999
Last updated November 20, 2008
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