On February 3rd, 2010, the European Journal of Clinical Nutrition published a study on the acute effects of caffeinated coffee and decaffeinated coffee on endothelial function of 20 healthy workers, volunteers of a hospital, concluding that caffeinated coffee decreases the endothelial function in 22.1%.
Source: Milenka Palacios Chávez
The endothelium or the inner membrane of the arteries regulates the blood flow. When the blood flow through the arteries increases, the blood vessel, as part of its natural function, expands, what is known as flow-mediated dilation (FMD). This dilation mediated by the flow of blood is a measure for the abnormal function of the endothelium, which is used to assess cardiovascular risk.
The study was conducted during 3 months (November 2007 – February 2008) to 20 non-obese workers with normal levels of cholesterol, triglycerides, glucose, insulin, uric acid, blood pressure and heart rate. Moreover, they did not consume tobacco, nor drugs, nor eat chocolates or beverages with antioxidants that could reverse the effect of caffeine. Furthermore, they did not drink more than two cups of coffee a day or more than one commercial decaffeinated beverage a week.
Participants were assessed before, and 30 and 60 minutes after drinking 1 cup of caffeinated espresso coffee (130 mg of caffeine) or one cup of decaffeinated coffee (5 mg of caffeine) without sugar nor milk and so that the participants did not know what they were drinking.
The results indicated that the ingestion of caffeinated coffee for a short term in healthy subjects leads to a significant failure of the dilation of the endothelium. Since the reduction of this dilation was not observed after ingestion of decaffeinated coffee, the effects of caffeinated coffee on the endothelial function can be attributed to the presence of caffeine.
Possible explanations for the reduction of FM are that caffeine reduces the production of nitric oxide (a vasodilator), increases the production of hormones such as dopamine, which promotes the increase of heart rate and blood pressure, and of norepinephrine, which increases blood pressure by vasoconstriction.
For more information about the role of nitric oxide in the endothelium and the consequences of the endotelial dysfunction, see the following video: http://www.youtube.com/watch?v=w2L_vPSwu8g
So, on the contrary, the possible improvement of the endothelial function after drinking decaffeinated coffee could be attributed to the presence of antioxidants in coffee (chlorogenic acid and caffeic acid), which are no longer inhibited by the high content of caffeine that was present before.