The study, which involved healthy, non-diabetic men, used green coffee polyphenols that were free of caffeine. Results of the randomized acute clinical intervention study with crossover design indicated that the polyphenols significantly increased a measure called reactive hyperemia index (RHI), which is a transient increase in blood flow, and an indicator of endothelial function.
The endothelium performs many functions including maintaining the suppleness of blood vessels and regulating the activity of neutrophils, white blood cells that form a key part of the immune system.
Dysfunction in the endothelium leads to arteries with little suppleness, raising the risk of high blood pressure (hypertension), and arteries that are chronically inflamed, leading to an overabundance of adhesion molecules.
Coffee, one of the world's largest traded commodities and generating more than $70bn in retail sales a year, has come under increasing study with research linking it to reduced risk of diabetes, and improved liver health.
As a source of polyphenols, one cup of coffee could provide 350 milligrams of phenolics, according to a review by Mario Ferruzzi from Purdue University in Physiology & Behavior (doi: 10.1016/j.physbeh.2010.01.035). Of these, the most abundant compounds in coffee are chlorogenic acids, making up to 12% of the green coffee bean. The most abundant of these compounds is caffeic acid.
However, the acute effects of these chlorogenic acids on endothelial function are mixed and the literature contradictory, wrote the Japanese authors of the new study in the journal Nutrition Research.
“The reasons for the discrepant responses remain to be elucidated; however, the caffeine and chlorogenic acid dose in the beverages is hypothesized to have a role,” wrote the authors, from the Health Care Food Research Laboratories at the Kao Corporation, and the Kagoshima University Graduate School of Medical and Dental Sciences.
“The substance responsible for the improved endothelial function after a single ingestion of coffee beverages has not been identified; however, this study indicates that the chlorogenic acids are strong candidates.
“These findings suggest that a single ingestion of coffee polyphenols improves peripheral endothelial function after glucose loading in healthy subjects and thus might have the potential to prevent coronary heart disease.”
The Japanese scientists used coffee polyphenols prepared from green coffee beans using hot-water extraction. This extract was subsequently spray-dried and ground.
Fifteen healthy Japanese men were randomly assigned to consume a 75-g glucose load with or without these coffee polyphenols. Results showed that blood glucose and insulin levels increased after both interventions, and there were no differences between the groups.
The reactive hyperemia index significantly increased in the polyphenol group, compared to baseline levels, said the researchers.
“These findings suggest that a single ingestion of CPP improves peripheral endothelial function after glucose loading in healthy subjects,” they concluded.
Source: Nutrition Research
Published online ahead of print, doi: 10.1016/j.nutres.2013.11.001
“Coffee polyphenols improve peripheral endothelial function after glucose loading in healthy male adults”
Authors: R. Ochiai, Y. Sugiura, Y. Shioya, K. Otsuka, Y. Katsuragi, T. Hashiguchi