Significant changes in our knowledge and approach towards lactose intolerance over the past quarter century has inspired us to present an updated review of lactose intolerance in infants children and adolescents. Differences between primary, secondary, congenital and developmental lactase deficiency are discussed. Children with suspected lactose intolerance can be assessed clinically by dietary lactose elimination or by tests including non invasive hydrogen breath testing or invasive intestinal biopsy determination of lactase ( and other disaccharidases) concentration. Treatment consists of use of lactase treated dairy products or oral lactase, supplementation, limitation of lactose containing foods or dairy products. Dairy food is an important source of calcium for bone mineral health and of other nutrients that facilitate growth in children and adolescents. If dairy products are eliminated, other dietary sources of calcium or calcium supplements need to be provided.

Keywords: abdominal pain, breath tests, calcium, dietary, dairy products, diarrhea, flatulence, lactase, malabsorption

American Academy of Pediatrics committee on nutrition presented a revised statement updating initial statements of 1978 (1) incorporating changes from 1990 supplements (2) and current state of art regarding lactose intolerance with updated recommendations regarding dietary calcium (3).

Lactose, a disaccharide that comprises monosaccharides, glucose and galactose, is the primary carbohydrate found extensively in human milk and most standard cow milk based formulas. Lactose is manufactured in mammary epithelial cells from glucose by a reaction involving α- lactalbumin (4). Lactose is specific nutrient for infancy supplying 40% of baby's energy needs, facilitates calcium and iron absorption, promotes healthy gastrointestinal tract (GIT) microflora, provides galactose which is incorporated as galactolipids into tissues of central nervous system. (5) Absorption of lactose requires lactase activity in small intestinal brush border to split the bond linking the 2 monosaccharides. A β. galactosidase termed 'lactase phlorizin hydrolase' (lactase) accounts for most of lactase activity in the intestinal mucosa. (6) Lactase is found in small intestines and localized to the tip of villi, a factor of clinical importance when considering the effect of diarrhoeal illness on the ability to tolerate milk.

Milk intolerance may be attributed to either lactose or protein content. Lactose intolerance can occur among infants and young children with acute diarrheal disease, although the clinical significance of this is limited except in more severely affected children. Symptoms of lactose intolerance are relatively common among older children and adolescents; however associated intestinal injury is infrequently seen. Lactose intolerance is a distinct entity from cow milk-protein sensitivity, which involves immune system, and causes varying degree of injury to intestinal mucosal surface. Cow milk protein intolerance is reported in 2% to 5% of infants within first 1-3 months of life, typically resolves by 1 yrs of age. (7,8)

Pediatricians and other pediatric care providers should maintain, awareness of the benefits and controversies related to consumption of dietary milk products and milk based infant formula. Lactose content of the milk often influences the ultimate decision about the use or continuation of milk in diet. Milk and dairy product avoidance has a negative effect on calcium and vitamin D intake in infants, children and adolescents. Other nutrients such as protein make dairy products an important source of nutrition for growing children.