Whatever your tipple, too much of it and you'll suffer the next day. Yet it's commonly thought that dark-coloured alcoholic drinks such as bourbon produce worse hangovers than colourless alternatives such as vodka. Damaris Rohsenow and colleagues now provide experimental evidence of this (D. J. Rohsenow et al. Alcoholism Clin. Exp. Res. doi:10.1111/j.1530-0277.2009.01116.x; 2009). They also find that hangovers caused by these drinks impair performance in tasks requiring both sustained attention and speed, and that the impairment correlates with the severity of the hangover, but not the colour of the drink.
The colours of alcoholic drinks are often due to congeners — compounds other than alcohol (ethanol) that form during the fermenting process. Bourbon contains 37 times more congeners than vodka, for example. Although the main cause of hangover symptoms is ethanol, congeners are thought to make matters worse.
Rohsenow et al. assessed this theory in a controlled study in which subjects drank vodka or bourbon until their blood alcohol concentration reached an intoxicating level. The intensity of the subjects' hangovers was quantified the next day using a symptom-based scale, and the subjects were given tests to measure their performance in tasks requiring speed and/or sustained concentration. Because alcohol affects the quality and duration of sleep, the authors also monitored these effects in their subjects.
Sure enough, bourbon caused worse hangovers than vodka, and all of the subjects experienced lighter, more disturbed sleep after alcohol consumption than they did when given a placebo (decaffeinated cola). But the effects of bourbon on sleep and on next-day performance in tests were no worse than those of vodka. What's more, although the amount of alcohol-induced sleep disturbance correlated with hangover severity, it was not responsible for the effects on performance in the tests.
Older subjects, or those dependent on alcohol, might have behaved differently from the young, healthy people who took part in the research. Nevertheless, as the authors point out, these findings have implications for people working in safety-sensitive jobs — as well as providing insight into how you feel the morning after the night before.
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Mitchinson, A. Uncongenial congeners. Nature 462, 992 (2009). https://doi.org/10.1038/462992a