Lactose malabsorption among adult Indians of the Great Basin and American Southwest.

The prevalence of primary adult lactose malabsorption and the pattern of milk use were studied among 109 Indians from various tribes of the American Great Basin and Southwest. Included were 100 persons who reported being full-blooded Indians as well as three with Mexican admixture and 6 with some European ancestry. Lactose malabsorption was found in 92% of the full-blooded Indians but in only 50% Indians who acknowledged European admixture. These results agree with those of studies of native Americans done elsewhere which show very high prevalences of such lactose malabsorption among adults reported as fullblooded and lower prevalences among individuals with admitted European ancestors. The suggestion made is that in pre-Colombian times, before interbreeding with Europeans began on any scale, such lactose malabsorption may have been nearly universal among native American adults. Most of the Indians studied consumed abundant milk since childhood but were nevertheless predominantly malabsorbers as adults. This argues against the induction hypothesis advanced by some to explain the striking ethnic differences that occur around the world in primary adult lactose malabsorption.