A growing body of medical evidence suggests that moderate daily alcohol consumption can be good for the heart. But what qualifies as "moderate drinking?"
A new Canadian study suggests one drink is fine, but two may be too many - at least in one sitting.
For the study, the researchers asked volunteers to consume a variety of drinks - red wine, diluted ethanol (pure alcohol) and water - while measuring their physical reactions.
One alcoholic drink had no significant effect on blood pressure, heart rate or the nervous system. But it did cause arteries to dilate, or open up, allowing blood to flow more easily through the vessels and thus reducing strain on the heart.
Two drinks, however, increased blood pressure, heart rate as well as nervous system activity. To make matters worse, the ability of the blood vessels to expand in response to the increase in blood flow was diminished, according to the findings published in the American Journal of Physiology - Heart and Circulatory Physiology.
"This experiment suggests that one drink may give you some of the putative benefits of alcohol, but many of those benefits may be lost if you increase the blood alcohol concentration quickly with two drinks," said lead researcher John Floras of the Peter Munk Cardiac Centre of the Toronto General Hospital.
In the study, two glasses of wine were downed within 1.5 hours.
He said it may still be fine to have two drinks a day, provided they are not consumed too close together. "If we space the time out and have a second drink four or so hours later, it might have a different effect on the heart," he said.