The research was a real-time study of 13 volunteers to determine whether a red wine with a verified high polyphenol content differs from alcohol in its effects on specific markers associated with a greater risk of high blood pressure, coronary artery disease and heart failure.
Researchers at the Peter Munk Cardiac Centre of the Toronto General Hospital found that though after one drink of either red wine or alcohol, blood vessels were more 'relaxed' or dilated, which reduced the amount of work the heart had to do.
However, after two drinks, the heart rate, amount of blood pumped out of the heart, and action of the sympathetic nervous system all increased.
At the same time, the ability of the blood vessels to expand in response to an increase in blood flow diminished. This counteracted the beneficial effect of one drink of red wine or alcohol.
"We had anticipated that many of the effects of one ethanol drink would be enhanced by red wine. What was most surprising was how similar the effects were of red wine and ethanol. Any benefits that we found were not specific to red wine," said Dr. John Floras, Director of Cardiology Research at the Peter Munk Cardiac Centre, and at Mount Sinai Hospital, in whose laboratory the study was performed.
However, Dr. Floras has warned that this study measured the effects of these drinks on one occasion only. The effects of daily wine or alcohol intake may be quite different.
For the study, healthy, non-smoking adults who were not heavy drinkers or total alcohol abstainers were examined.
Participants attended three separate morning sessions during which 'standard' drinks of red wine, ethanol or water were administered at random, single blind, and two weeks apart.
The findings showed that one drink of either red wine or alcohol has no effect on heart rate, blood pressure or sympathetic nerve activity, which activates the 'fight or flight' reaction and generally modulates heart rate and sets the diameter of blood vessels in order to redistribute blood; and dilates the brachial artery.
On the other hand two drinks of either alcohol or red wine increase sympathetic nerve activity, heart rate, and the amount of blood the heart pumps out, and also blunt the ability of the brachial artery to expand further in response to blood flow.
Rise in heart rate and sympathetic nerve activity are recognized markers for hypertension, heart failure and sudden death.
"Our findings point to a slight beneficial effect of one drink - be it alcohol or red wine - on the heart and blood vessels, whereas two or more drinks would seem to turn on systems that stress the circulation," Dr. Floras said.