Distribution of the adult lactase phenotypes in Turkey.

The adult lactase phenotype, lactose absorber or malabsorber, was determined using the lactose tolerance test with breath hydrogen assay in a group of young, healthy, male Turks. Out of a total of 470 subjects, 135 (28.7%) were lactose absorbers and 335 (71.3%) lactose malabsorbers. The frequency of the 'lactase suppression gene' in this population sample was 0.844 (S.D. 0.012). The frequency of lactase suppression in Turkey is intermediate between that in southeast Europe and that in agricultural Arab populations and thus compatible with a genetic cline extending from Europe to southwest Asia.