Table 1.

Definition of hypolactasia, lactase non-persistence, lactose malabsorption, and lactose intolerance (modified from [14]).

Hypolactasia	Any deficiency of the lactase enzyme
Lactase non-persistence	This is considered the “wild-type” condition, as most individuals have reduced lactase activity at the jejunal border after weaning. In a minority of humans, a high level of activity of the lactase enzyme is present through all adulthood (lactase persistence phenotype)
Lactose maldigestion	Inefficient digestion of lactose, due to lactase deficiency (either lactase non-persistence or other intestinal conditions)
Lactose malabsorption	Inefficient absorption of lactose, due to lactose maldigestion, as lactose cannot be absorbed in the undigested form
Lactose intolerance	Gastrointestinal symptoms due to lactose malabsorption