Chlorogenic acid and other antioxidants
Explanations for the association between coffee consumption and lower rates of heart disease and diabetes often point to chlorogenic acid and other obscure antioxidant substances as the responsible parties. Antioxidants are substances that sop up reactive molecules before they have a chance to harm sensitive tissue like the lining of blood vessels. Chlorogenic acid was probably the main antioxidant in your cup of coffee this morning. Some experiments have shown that it may also inhibit absorption of glucose in the digestive system and even out insulin levels.
Chlorogenic acid might be another coffee ingredient with a split personality. Along with caffeine, it seems to push up levels of homocysteine, an amino acid that has been associated with artery-clogging atherosclerosis.