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Rob van Dam, PhD, adjunct assistant professor of nutrition at Harvard School of Public Health

For most of us, java isnt harmful.
Its true that caffeine may raise blood pressure, so if you have hypertension, its smart to switch to decaf. Caffeine can also interfere with sleep; if you suspect its causing you to toss and turn, cut back. Otherwise, there is no health reason to stop drinking it.

It may lower your risk of becoming diabetic.
Every cup of coffee you drink seems to reduce your risk of the disease. In fact, a review of research in Archives of Internal Medicine found that after three or four cups a day, you see a 25 % lower risk. Other research shows that decaf may also cut your risk of diabetes, which suggests that its not the caffeine but something else in coffee, possibly an antioxidant called chlorogenic acid, thats responsible. Coffee drinkers may also be less likely to develop cirrhosis of the liver and liver cancer.

Caffeine may have its own benefits.
It could reduce your risk of Parkinsons disease and possibly even Alzheimers. Thats not a reason to start consuming it, but its good news if you already enjoy a cup of joe.

James D. Lane, PhD, director of the Duke University Medical Center Psychophysiology Laboratory

The research on coffees perks is weak.
The main problem is that many studies compare coffee drinkers with people who dont drink coffee. Coffee drinkers may have something else in common thats the true cause of these benefits. Just because two things are correlated doesnt mean that one causes the other.

It can make health conditions worse.
The caffeine in coffee does have negative effects, especially for people with high blood pressure or diabetes. In one study, hypertensives blood pressure came down a bit after they quit coffee for a week. In another study, we found that giving diabetic patients caffeine before giving them a glucose tolerance test made their blood sugar rise higher than when they didnt have caffeine. In other words, for people who already have diabetes, it appears to make the condition worse. Decaf, however, is fine.

Your brew can aggravate stress.
My studies have shownthat adrenaline responses to stress are higher if youve had caffeine than if you havent—it may make you more tense, anxious, andjittery, in addition to giving you sleep problems.

Our advice:
If you dont have diabetes or high blood pressure, a coffee habit probably doesnt hurt—and may even help your health. While research suggests that some people are more sensitive to caffeine than others, theres no need to cut back unless you suffer from anxiety or insomnia, in which case you may want to switch to decaf.

If you dont drink coffee, theres no reason to start: Adding fruits, vegetables, and whole grains to your diet is a surer way to reduce disease risk.