Before lactose can be absorbed by the body, it must be hydrolysed to its two components, glucose and galactose, by the enzyme lactase.¹ A deficiency of this enzyme can result in lactose malabsorption.⁴ Lactose that is not absorbed is fermented by the gut microbiota which results in the production of gases such as hydrogen, carbon dioxide and methane. Lactose intolerance is clinically defined as substantial lactose malabsorption associated with gastrointestinal symptoms such as bloating, abdominal pain, diarrhea and vomiting.⁴

Normal, healthy infants are born with the ability to tolerate lactose as it is the primary carbohydrate of breastmilk. In most infants, intestinal lactase activity reaches its maximum at birth.¹ Some children experience a physiological gradual decline of lactase activity (hypolactasia) after weaning, however, significant gastrointestinal symptoms generally do not occur before 5 years of age.³ The peak onset of hypolactasia related gastrointestinal symptoms occurs in adolescence and adulthood.³