Remember when people (and their doctors) used to worry that coffee was bad for the heart, would give them ulcers, and would make them overly nervous?

In excess, it can cause problems. But recent research has linked coffee to health benefits, not harm, including possible (it’s not a done deal) protective effects from everything from Parkinson’s disease to diabetes to some types of cancer.

The January 2012 issue of the Harvard Health Letter looks at some of the ingredients in coffee that might explain its possible positive effects:

Caffeine. Caffeine probably has multiple targets in the brain, but the main one seems to be adenosine receptors. A part of the brain affected by Parkinson’s disease, called the striatum, is loaded with adenosine receptors. By docking on them, caffeine may have some protective effects against the disease. Caffeine has some negative short-term effects on the cardiovascular system, raising blood pressure and perhaps making arteries stiffer. But habitual use may cause some of those effects to wear off.

Cafestol and kahweol. Coffee contains oily substances called diterpenes; the two main types are cafestol and kahweol. They may have anticancer effects, but they also have a downside, increasing cholesterol levels. Coffee filters trap most of the cafestol and kahweol so they don’t wind up in the beverage that people drink.

Antioxidants. Antioxidants are substances that sop up reactive molecules so they don’t harm sensitive tissues like those that line the inside of blood vessels. Coffee contains a fair amount of antioxidants, including a powerful one called chlorogenic acid.

Vitamins and minerals. Coffee isn’t a great source of vitamins and minerals, but it does contain small amounts of magnesium and potassium.

Read the full length article: "What is it about coffee?"