The vices of tolerance

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CONVENTIONAL wisdom has it that people who hold their liquor pretty well can drink with impunity. Not so, apparently. According to an 18-year-long study by Marc Schukit and Tom Smith, at the University of California, San Diego, the reverse is true: youthful tolerance presages alcoholism in later life.

Over the course of their study, Dr Schukit and Dr Smith have followed the drinking careers of 450 men. Each of their subjects entered the trial as a healthy, non-alcoholic 18-29-year-old. At the beginning, each was tested in an attempt to determine how his body and mind responded to a given amount of alcohol (the dose varied with the subject's weight). Dr Schukit and Dr Smith measured how the level of cortisol (a hormone released in response to alcohol) rose in each subject's bloodstream. They measured how much he swayed after he drank. And they asked him to assess how giddy it made him feel.

Some subjects, as in the wider world, were unaffected. Their cortisol levels scarcely budged, they stood steady as rocks, and they did not feel drunk. Others soon became squiffy. Perhaps surprisingly, this response did not depend on how much or how often each man was drinking routinely-it was not, in other words, a question of practice. It did, though, depend quite significantly on whether or not his father was (or subsequently became) an alcoholic.

Dr Schukit and Dr Smith called their subjects back in after eight years to see what had happened in the interval. Around 60% of the "hollow leg" groupthose who, as younger men, had shown high tolerance of alcohol-were found to alcoholics. By contrast those of their counterparts who, in the first phase of the study, had got tipsy on the test dose, had a less-than-15% chance of becoming alcoholics.

The two researchers see a strong genetic influence in this pattern. They tried to control for the possible psychological impact of having an alcoholic father by looking for signs of depression, anxiety and other emotional disturbance in their subjects when they recruited them. There was no discernible link between these pre-existing conditions and eventual alcohol abuse.

On the other hand, it was not the possession of an alcoholic father that predicted the problem, but the high tolerance of alcohol, regardless of father. If genes are involved in creating the tolerance(quite likely), and the subsequent alcoholism (also plausible), it would tend to run in families. But several genes are probably at work. These would need to be present in the right combination to put someone at risk. Sometimes, therefore, parental symptoms may be absent even though some of the relevant genes are carried by each. Like father is not necessarily like son.

The Economist