Wednesday, February 13, 2008

A Standard Glass or Two...or More?

UPDATE February 19, 2008: Dr Spaak has confirmed that the calculation used to determine the alcohol content was in error (see below).

Canadian researchers have come up with data showing that, unlike one drink, two drinks significantly increases several measures of heart function. Seems about right, I know two glasses of a good wine will increase my heart rate! Although I never find myself all that stressed about it. I wonder why? Should we take this research at face value?

The amount of wine ingested was adjusted for body weight and sex so that one glass (155 ml, or 5.2 oz) of wine with 12% alcohol content given to a 68-kg man equaled 18.6 g of ethanol; the wine was a Wolf Blass 2001 pinot noir (1). The first drink was ingested over 5 min, and the second when blood alcohol had fallen to 25–30 mg/dl. Based on Figure 1 in the study it looks as though both drinks were consumed within one hour. Consuming two drinks in an hour is probably reasonable but one in 5 min is pretty quick, at least for me.

Another problem is the amount of alcohol given. Their own statement argues that they consider one drink to contain 18.6 grams of ethanol. Not only is this high but it seems to be an error brought about by confusing the alcohol content by volume rather than weight. If calculated on a volume per volume basis then 155 ml of a 12% (ABV) wine equals 18.6 mls of alcohol, but not 18.6 grams of alcohol as alcohol (ethanol) is lighter than water (density of ethyl alcohol is 0.789g/ml). So one drink (155 ml of a 12% ABV wine) contains 14.7 grams of alcohol, and two drinks contains 29.4 grams.

In Australia a standard drink is 10 grams of alcohol (calculated using the density of ethyl alcohol as 0.789). In the USA one standard drink is 13.7 grams of alcohol. So the study subjects getting two drinks or 37.2 grams of alcohol consumed 3.7 standard Australian drinks and 2.7 standard USA drinks. If they consumed 29.4 grams then they consumed 2.9 standard Aussie drinks and 2.1 standard USA drinks.

If the authors of the study have made an error in calculation (and its possible that the error only exists in the figure legend) then their study still has relevance. Its all a matter of what you define as a standard drink. I’d also like to know if you really need to drink that first glass in five minutes to get arterial dilation?

1) The verbatim quote from part of the legend to Figure 1 is as follows “The first dose (dose 1) of wine or ethanol in the present study was adjusted for body weight and sex to reflect 1 glass (155 ml, or 5.2 oz) of wine with 12% alcohol content given a 68-kg man, which equals 18.6 g of ethanol.”

No comments: