More and more evidence is showing that coffee in moderation can be a healthy part of your diet. “Unsweetened coffee, either black or with a small amount of nonfat or low-fat milk, would be the healthiest option,” says Kennedy. Coffee drinkers may have a lower risk of developing heart disease, type 2 diabetes, and certain types of cancer. According to a study published in March 2011 in the journal Stroke, women who drink a cup or more of coffee a day have up to a 25 percent lower stroke risk as compared with nondrinkers.
And — as if you didn't know it already — coffee's caffeine can help with mental alertness and physical performance, as long as you don't overdo it. Too much caffeine can leave you jittery and anxious, so dietitians generally recommend that you drink no more than a couple of cups a day (depending on the way it's prepared).
“It’s generally considered safe to have up to 400 milligrams of caffeine each day,” says Kennedy. “Certain types of brewing will have different amounts of caffeine.” And some people are more sensitive to caffeine than others. Pregnant women and those trying to become pregnant may want to avoid it, though research on this is mixed.