According to the findings, 8.9 percent of the fathers and 1.6 percent of the mothers who gave their offspring up for adoption had been hospitalized for alcoholism. Heath and colleagues (in press) estimated that the proportion of all adults in the population of Copenhagen who were in the same age range as the biological parents and who had been hospitalized for alcoholism at some stage in their lives was 2 percent for men and 0.5 percent for women. These figures are almost certainly overestimates. Compared with what would be expected for the population as a whole, the lifetime prevalence of hospitalization for alcoholism is at least four times higher in the biological fathers and three times higher in the biological mothers of the children who were given up for adoption. Therefore, if alcoholism is genetically influenced, then adoptees as a group would be at higher risk than the general population and would have elevated rates of alcoholism. The higher genetic risk among adoptees is a recurrent finding in the major adoption studies and should be taken into consideration when analyzing results.
