That boost you get from your morning cup of java isn't imaginary. Alertness, cognitive performance, and some measures of physical ability do improve after a modest amount of caffeine. And coffee may have other, more surprising health benefits as well. A June 2008 study of 130,000 people followed for two decades, published in the Annals of Internal Medicine, linked regular coffee drinking with longer life.

But coffee has a dark side as well. Too much can make you jittery and interfere with your ability to concentrate. Skip your morning dose and you may suffer caffeine-withdrawal headaches. And caffeine or other substances in coffee may weaken the bones and cause other health problems, at least in some people.


Coffee's perks

Here's how coffee may help your health.

Heart and brain protection. The lower mortality rate among coffee drinkers in the 2008 study stemmed mostly from a reduced risk of death from heart attack and stroke, especially in women. Those who consumed between two and five cups a day had about a 30 percent lower risk of cardiovascular death compared with those who had less than one cup a month. Drinking more than five cups a day didn't seem to provide extra benefits but didn't seem to hurt either.

Researchers don't know what accounts for that apparent benefit, but it doesn't seem to be caffeine. The decaf drinkers got a boost similar to those who drank regular coffee. Antioxidant compounds, called phenols, in coffee beans may provide some of the health boost, since preliminary research suggests they may help prevent potentially deadly blood clots from forming.

Fears that coffee raises blood pressure and increases the risk of abnormal heartbeats have been calmed by recent studies. But other research does suggest that unfiltered coffee, such as that made in French press coffeemakers, contains a fat-like compound called cafestol that can raise levels of LDL (bad) cholesterol.

And according to one study, getting 200 milligrams of caffeine—the amount in about two cups of coffee—before exercise might reduce blood flow to the heart, a risk to people with heart disease.

Blood-sugar control. The heart-healthy phenols in coffee may also help regulate blood sugar levels, according to a few studies. That may help explain why coffee consumption has been linked to a lower risk of developing type 2 diabetes.

Gallbladder health. Caffeine appears to stimulate gallbladder function and prevent bile from crystallizing into painful gallstones.

Parkinson's disease prevention. Caffeine may protect against the disease by boosting the supply of the neurotransmitter dopamine to the brain.


Grounds for concern

Drinking caffeinated beverages before bed can obviously undermine sleep. And too much caffeine may contribute to the health problems described below.

Weak bones. Large amounts of caffeine increase the excretion of calcium in urine, which might weaken bones and increase risk of kidney stones. And it can undermine the effectiveness of the bone-building drug alendronate (Fosamax and generic).

Heartburn and stomach pain. The acids in regular and decaf coffee can inflame the esophagus, contributing to heartburn, and the stomach, which can provoke gastritis, a problem marked by upper abdominal pain accompanied by belching, bloating, and nausea.

Pregnancy problems. High doses of caffeine might lead to lower birth weight in babies. And drinking more than five cups a day appears to double the risk of spontaneous abortion, one well-designed study found.

Drug interactions. Caffeine can interact with several medications, including certain antidepressants and antipsychotics, increasing the risk of side effects.


Recommendations

Moderate coffee consumption (one to two cups per day), both regular and decaffeinated, is safe and possibly healthful for most people. But certain individuals may need to take some precautions:


This article first appeared in the November 2008 issue of Consumer Reports on Health.