Tea is the most popular beverage worldwide (after water), but coffee is close behind it in industrialized countries. While caffeine is a natural component of both tea and coffee, coffee contains more of it: anywhere from 60 to 120 milligrams in six ounces, depending on brewing methods and other factors. Caffeine is a mild psychoactive substance—it stimulates the central nervous system and improves alertness. It also boosts the analgesic effect of aspirin and other pain relievers, which is why it's added to some of these drugs. In large enough amounts, it can cause heart palpitations, stomach upset, and insomnia.

Coffee, derived from a bean, contains many other phyto-chemicals besides caffeine, and some of them may have beneficial effects in the body, as do those in tea, though this aspect of coffee is only beginning to be studied. Coffee itself has been extensively studied for years, generally to see if it causes disease. While many people believe decaf is more healthful than regular, there's no proof that it is.

Coffee has been blamed for causing many ailments, but in nearly every instance, it has been declared not guilty.

• It was linked to heart disease, as well as pancreatic cancer—but then exonerated. Research suggesting such links hasn't been supported by subsequent studies. Some researchers still worry that coffee drinking may promote hypertension—but many studies have failed to show that it does. When risk factors like cigarette smoking and heavy alcohol consumption are taken into account, any apparent link between coffee and heart attacks disappears.

• Coffee was blamed for fibrocystic breast disease (lumpy, painful breasts), but there proved to be no connection.

• Coffee was a suspected risk factor for osteoporosis, but it does not appear to increase the risk, even in heavy coffee drinkers—though there is still some controversy about this. (It's true that heavy coffee consumers are more likely to eat poorly and smoke, which boosts the risk of osteoporosis.)

• Coffee was suspected of raising the risk of miscarriage and birth defects, but—again—studies haven't supported this, except perhaps for high intakes. Some researchers are still not willing to let coffee off the hook. Pregnant women should probably drink no more than a cup or two a day.

Research on coffee continues. Here are the latest news tidbits:

• According to one well-designed study in Honolulu, coffee may reduce the risk of Parkinson's disease. Men who drank no coffee were two to three times more likely to develop the disease than those who drank one to four cups a day, and five times more likely than those who drank more than four cups a day. The caffeine was identified as the protective substance. No one can adequately explain this, and it's only a single study, with many limitations. But it's worth investigating further.
• In another study, those who drank two or three cups of coffee daily cut their risk of gallstones by 40%. Again, there's no explanation for this—and it's only one study. It's far too early to recommend coffee for this purpose.

The studies continue, occasionally raising a few worries. As we've reported, studies have shown that drinking five to eight cups a day of unfiltered coffee—European-style coffee, made in a French press (a pot with a plunger)—raises blood cholesterol. The great majority of coffee consumed in the U.S. and Canada is filtered. And anyway, that's a lot of coffee.

Another study found that drinking lots of coffee may increase the risk of urinary incontinence. The solution: cut down.

The bottom line is still this: If you're healthy it's fine to drink coffee in moderation (no more than three or four cups a day). If you like the lift it gives, and the sociability it affords, there's no health reason to deprive yourself of coffee. If you overindulge and get coffee nerves, the remedy is simple—cut back. If it keeps you awake, stick to decaf in the evening.