Because of their obvious relationship to the disposition of alcohol in the body, studies have examined the relationship between genes encoding alcohol and aldehyde dehydrogenases and several GI diseases. Variants in ADH and ALDH genes that at least transiently increase acetaldehyde levels generally reduce heavy drinking and risk for alcoholism, as noted above. But among those who drink heavily despite this, the same genes may increase cancer risk by increasing levels of acetaldehyde in the tissues29, 80, 82-86. Studies have been complicated by the difficulty in disentangling these effects, and by the fact that many variants among the ADH genes are in significant linkage disequilibrium (at least partially co-inherited).
