The role of thiamine deficiency in alcoholic brain disease

Alcohol Research & Health, Spring, 2003 by Peter R. Martin, Charles K. Singleton, Susanne Hiller-Sturmhofel

Acute alcohol exposure interferes with the absorption of thiamine from the gastrointestinal tract at low, but not at high, thiamine concentrations (Hoyumpa 1980). Furthermore, in studies using rats, the activity of the TPK enzyme from various tissues decreased with acute alcohol exposure to about 70 percent of the activity level in control animals, and with chronic alcohol exposure to about 50 percent (Laforenza et al. 1990). Although no studies have addressed whether alcohol directly affects TPK in humans, indirect analyses have found that the ratio of phosphorylated thiamine (primarily ThDP) to thiamine is significantly lower in alcoholics than in nonalcoholics (Poupon et al. 1990; Tallaksen et al. 1992)--that is, that less thiamine is converted to ThDP. This finding suggests that TPK is less active in the alcoholics.

Thiamine malabsorption could become clinically significant if combined with the reduced dietary thiamine intake that is typically found in alcoholics, when other aspects of thiamine utilization are compromised by alcohol, or when a person requires increased thiamine amounts because of his or her specific metabolism or condition (e.g., in pregnant or lactating women).

Impaired Thiamine Utilization

The cells' utilization of thiamine can be affected in different ways by chronic alcohol use. As mentioned earlier, once thiamine is imported into the cells, it is first converted into ThDP by the addition of two phosphate groups. ThDP then binds to the thiamine-using enzymes, a reaction that requires the presence of magnesium. Chronic alcohol consumption frequently leads to magnesium deficiency, however (Morgan 1982; Rindi et al. 1992), which also may contribute to an inadequate functioning of the thiamine-using enzymes and may cause symptoms resembling those of thiamine deficiency. In this case, any thiamine that reaches the cells cannot be used effectively, exacerbating any concurrently existing thiamine deficiency.

Abstinence from alcohol and improved nutrition have been shown to reverse some of the impairments associated with thiamine deficiency, including improving brain functioning (Martin et al. 1986). Researchers also administered thiamine to alcoholic patients and laboratory animals and found that this treatment reversed some of the behavioral and metabolic consequences of thiamine deficiency (Victor et al. 1989; Lee et al. 1995). Most recently, researchers administered different thiamine doses for two days to a group of alcoholics undergoing detoxification, none of whom were diagnosed with WKS, and then tested the participant's working memory. These studies found that participants who received the highest thiamine dose performed best on tests of working memory (Ambrose et al. 2001).

DIFFERENTIAL SENSITIVITY TO THIAMINE DEFICIENCY

Differences in Sensitivity Among People

Several findings suggest that not all people are equally sensitive to thiamine deficiency and its consequences. For example, although thiamine deficiency may occur in up to 80 percent of alcoholics (Tallaksen et al. 1992; Hoyumpa 1980; Morgan 1982), only about 13 percent of alcoholics develop WKS (Harper et al. 1988). This means that the severest consequences of thiamine deficiency develop only in a subset of people who consume alcohol and have poor nutrition on a chronic basis. A possible explanation for this differential sensitivity is that some people are genetically predisposed to develop brain damage after experiencing repeated episodes of alcoholrelated thiamine deficiency. To investigate this hypothesis, researchers have studied the activities of thiamine-using enzymes in patients with and without Korsakoff's psychosis, arguing that variants of these enzymes may exist that could differ in their susceptibility to thiamine deficiency. The results of these investigations, however, have been inconsistent. (2)