Evidence suggests that tea contains high amounts of antioxidants. These antioxidants have been measured and their bioavailability in humans evidenced. Green tea is particularly high in catechins (flavan-3-ols) and black tea contains high amounts of theaflavins and thearubigins. These chemicals may act as antioxidants in humans and may confer protection against disease. Tea consumption shows inverse associations with various forms of cancer (most notably of the gastrointestinal tracts) as well as cardiovascular disease and obesity. The health benefits of tea have largely been attributed to the antioxidants it contains. However, coffee is also a good source of antioxidants. As with tea, coffee contains a number of phenolic compounds of which chlorogenic acid is the most prevalent. As with tea phenolics,. Coffee phenolics are likely extensively metabolised in the gut prior to absorption, and this may result in the generation of a large number of products including caffeic acid and ferulic acid.
Like tea, coffee contains a high concentration of antioxidant compounds. In coffee these are most prevalent as chlorogenic acid, an ester of caffeic acid. As with tea, coffee phenolics are extensively metabolised in the gut and this makes determining the chemical composition of the absorbed fraction very difficult to determine. Rather than the effects of coffee being attributed to a single compounds, it is much more likely that a range of phenolic compounds are produced in the gut, including caffeic acid and ferulic acid. These compounds are absorbed and can be detected in whole blood. While it is unclear what biochemical effects these compounds have, some of the effects likely stem from the antioxidant potential they possess. As antioxidant capacity raises quickly and is transient, as with tea, regular consumption of coffee likely provides the most consistent antioxidant protection to the consumer.
Phenolic acids may confer particular health effects in humans. Some of these effects may stem from their antioxidant capacity, although other cellular effects may occur. Studies have investigated the effects of coffee consumption and shown that consuming coffee resulted in significant increases in ferulic acid and caffeic acid 1 hour post consumption. In addition, at 1 hour post consumption there was also a significant increase in the plasma antioxidant capacity of the plasma. Therefore the phenolic acids from the coffee could be providing significant levels of antioxidant compounds and this may in turn be improving antioxidant status. However, the absorption of phenolic acids may be limited by the absorption capacity of the gut, as medium and high levels of chlorogenic acids (420 mg and 780 mg) in coffee provide similar increases in antioxidant capacity (6 % and 5 %, respectively). It should be noted that the coffee in this study was filter coffee made from coffee beans, instant coffee may have different effects.
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