This is the first paper that presents data on absorption of chlorogenic acid and caffeic acid in humans. Chlorogenic acid and caffeic acid are important phenolic compounds in our diet. The interest in these compounds is increasing because phenolic compounds are antioxidants in vitro. Antioxidants are believed to contribute to the prevention of cardiovascular disease. However, knowledge on the absorption of these components is essential to evaluate potential health effects. We showed that chlorogenic acid and caffeic acid are absorbed in humans which increases the possibility that they might affect health.

We investigated the absorption of caffeic acid and chlorogenic acid in healthy volunteers without a colon (ileostomy volunteers). In such subjects degradation of the compounds by the colonic bacteria is minimal, and absorption can be calculated as the amount ingested minus the amount excreted in ileostomy effluent. This method offers a unique opportunity to measure actual absorption of orally ingested compounds in humans. We now show for the first time that the phenolic compounds caffeic acid and chlorogenic acid are absorbed in humans.

Phenols are antioxidants in vitro, but their antioxidant activity in vivo is uncertain. The effects of dietary compounds in vivo are in part determined by their bioavailability. Because the phenolic compound chlorogenic acid (an ester of caffeic acid and quinic acid) occurs in high amounts in coffee and daily intake is substantial, we were interested in the bioavailability. A main aspect of bioavailability is absorption, and information on absorption of chlorogenic acid in humans was lacking. Therefore we decided to investigate the absorption of chlorogenic acid and caffeic acid in humans as a first step in our project 'bioavailability and health effects of phenolic compounds in humans'. Peter Hollman (co-author) and his group also used the method with the ileostomy volunteers to calculate the absorption of quercetin, an important dietary flavonoid. They showed that the method with the ileostomy volunteers is very valuable. Therefore we decided to use this method for our study.

There is increasing interest in antioxidants because they might reduce disease risk. Dietary phenols are important antioxidants, but their bioavailability determines whether they can exert health effects in humans. There is information available on the bioavailability of these compounds, but this comes mainly from animal studies and in vitro studies. Data in humans are sparse. We showed for the first time that the absorption of chlorogenic acid and caffeic acid in humans is substantial. Therefore, potential effects of these compounds on human health can be expected. Furthermore, we showed that the absorption of caffeic acid is hampered when it is estrified with quinic acid (chlorogenic acid). This offers opportunities for modification of the absorption of these compounds. This work is an important contribution to the knowledge on behavior of phenolic compounds in the human body.

Margreet R. Olthof Ph.D.
Wageningen Centre for Food Sciences
Human Nutrition and Epidemiology
Wageningen
The Netherlands