Score one for java junkies. A recent analysis of the Nurses’ Health Study, a large, long-term investigation of factors that affect women’s health, has found a reduced risk of depression among coffee drinkers compared with people who do not drink coffee. Decaf appeared to have no significant effect on depression, nor did tea.

Of course, tea aficionados can point to other evidence that supports their drink of choice. Here’s a rundown on the evidence for both beverages.

Coffee contains antioxidant compounds called polyphenols, which may help regulate blood sugar and prevent deadly blood clots. In fact, regular (as opposed to occasional or infrequent) coffee consumption was associated with a longer life — mostly due to a reduced risk of heart attacks and strokes — in a 2008 study of nearly 130,000 people who were followed for two decades.

Tea is also rich in polyphenols, which, at least in laboratory studies using cell cultures and animals, have been found to help keep blood vessels healthy, reduce cholesterol, prevent the buildup of artery-clogging plaque and inhibit the growth of cancer cells. Fluoride and estrogen-like substances in tea might also bolster bone density, but further research is needed to confirm that benefit. Some evidence from population studies suggests that tea drinkers have a lower risk of heart disease and certain types of cancer, but that’s far from definitive.

Bottom line: Coffee and tea can be a healthful part of your diet. But don’t overdo the caffeine, which is easier advice for tea drinkers to follow, since coffee typically contains twice as much of the stimulant as black tea and about four times as much as green. Most healthy adults can safely consume up to 300 milligrams of caffeine daily (roughly three eight-ounce cups of coffee); pregnant women, fewer than 200 milligrams.

People who suffer from anxiety, headaches, palpitations or tremors may want to reduce or eliminate their consumption of caffeinated beverages to see if it helps.

The buzz on caffeine

Is caffeine safe? To put it in context, explains Neal Benowitz, professor of medicine at the University of California at San Francisco, caffeine is just one constituent of coffee and tea, which have many things in them. For caffeine itself, probably the most important risk is that it can precipitate a panic attack. If you ingest too much of it, you can get what’s called caffeinism: jitters and tremor. Caffeine can increase blood pressure and can aggravate heart arrhythmias.

However, if you consume caffeine on a regular basis, you develop a tolerance to most of its side effects. A study was done in which people were given the equivalent of 12 cups of coffee a day. At first they were wide awake and stimulated, and their blood pressure went up, but after three or four days those effects went away. As for heart disease, how you brew the coffee is a factor. French press or boiled coffee has chemicals that can raise cholesterol. But filtering coffee removes those chemicals; in fact, filtered coffee can actually protect the heart because it also contains antioxidants.

How much caffeine is too much? There aren’t a lot of harmful effects if you have a cup or two of coffee a day. But other things have caffeine, too, such as soft drinks and energy drinks. Guarana, an ingredient in many weight-loss and athletic-performance supplements, has caffeine in it. It would be nice if all these products were labeled so people could tell how much caffeine they’re getting.

Is caffeine addictive? You can clearly become physically dependent on caffeine, but that isn’t the same thing as addiction, in which you have a compulsion to use a substance and can’t easily quit even if you need or want to. Physical dependence means that when your body doesn’t have the substance, you get withdrawal symptoms. The most well-known symptoms of caffeine withdrawal are headache and a feeling of lethargy in the morning.

In itself, being dependent on caffeine isn’t harmful, but it can be inconvenient, especially if you’re traveling and don’t have access to coffee or another source of caffeine.