Senior author Chang Y. Lee, a professor of food science at Cornell University in Ithaca, N.Y., said raw coffee is, on average, just 1 percent caffeine, but it contains 7 percent to 9 percent chlorogenic acid, a strong antioxidant, which might slow the release of glucose into the bloodstream after a meal.
The researchers said chlorogenic acid might also prevent retinal degeneration in mice. The retina is a light-sensitive layer of tissue, lining the inner surface of the eye, which serves much the same function as the film in a camera. Light striking the retina initiates a series of chemical and electrical events which trigger nerve impulses sent to the brain via the optic nerve.
The retina is one of the most metabolically active tissues -- meaning it needs a consistently high and steady supply of uncontaminated oxygen. Without high levels of oxygen it is prone to oxidative stress -- a lack of this oxygen and production of free radicals leads to tissue damage and loss of sight.
A free radical is an atom, molecule or ion that has unpaired electrons or an open electron shell and one or more "dangling" bonds. For example, a hydroxyl radical -- HO -- is a molecule one hydrogen atom short of a water molecule and thus has one bond dangling from the oxygen which can react with other substances. Free radicals are thought to contribute to the aging process.
The scientists gave mice nitric oxide, which creates oxidative stress and promotes forming certain harmful free radicals, leading to retinal degeneration, which impairs and can ultimately contribute to the loss of sight.
However, the study published in the Journal of Agricultural and Food Chemistry, found the mice exposed to the nitric oxide who were pretreated with chlorogenic acid did not develop any detectable signs of retinal damage.
The study is "important in understanding functional foods, that is, natural foods that provide beneficial health effects," Lee said in a statement.
"Coffee is the most popular drink in the world, and we are understanding what benefit we can get from that."
Previous research linked coffee to reduced risk of Parkinson's disease, prostate cancer, diabetes, Alzheimer's and age-related cognitive declines.