Pediatric Lactose Intolerance Clinical Presentation

Updated: Oct 06, 2017
  • Author: Stefano Guandalini, MD; Chief Editor: Carmen Cuffari, MD  more...
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Symptoms of lactose intolerance include the following:

  • GI symptoms

    • Bloating, abdominal discomfort, meteorism, and flatulence that occur from 1 hour to a few hours after ingestion of milk or dairy products may signify lactose intolerance; however, other disorders such as milk-protein sensitivity, allergic-type reactions to other substances in the meal, or other saccharide intolerance may cause similar symptoms.

    • Many individuals with lactose intolerance are concerned about the presence of lactose in many orally administered drugs; however, one investigation concluded that no side effects are experienced by adults with hypolactasia upon ingestion of lactose-containing drugs. [5]

    • Adults and adolescents who have been diagnosed with lactose malabsorption appear able to tolerate as much as 12 g of lactose in a single dose (equivalent to the lactose content found in 1 cup of milk). Even larger amounts can be tolerated if they are ingested with meals and distributed throughout the day. However, 50 g of lactose (the lactose content found in 1 quart of milk) usually causes symptoms in adults with lactose malabsorption when administered as a single dose outside of meals. [2]

    • Although lactose intolerance is often suspected in children with functional recurrent abdominal pain, strong evidence suggests that lactose intolerance plays no role in such condition. [6]

    • Of note, although lactose (as well as fructose) intolerance is associated with gastrointestinal symptoms, the relationship of lactose malabsorption with symptoms in patients with functional gastrointestinal disorders is not clear. [7]

  • Associated food

    • The rate of gastric emptying is important in the development of symptoms, which may develop if lactose moves quickly to an intestine that is low in lactase. Fats decrease the rate of gastric emptying, whereas carbohydrates increase the rate of gastric emptying. Thus, if dairy products that contain lactose are ingested with carbohydrates, especially simple carbohydrates, symptoms are more likely.

    • Allergies to food proteins, particularly milk and grain proteins, can mimic lactose intolerance in part.

    • Inflammation of the intestinal mucosa due to infection or protein-sensitive enteritis causes secondary lactose intolerance.

  • Stool characteristics: Loose, watery, acidic stool often with excessive flatus and associated with urgency that occurs a few hours after the ingestion of lactose-containing substances is typical.

  • Gastroenteritis: Infectious diarrhea, particularly viral gastroenteritis in younger children, may damage the intestinal mucosa enough to reduce the quantity of the lactase enzyme. This does not result in any significant problem and does not require any changes in formula. However, intolerance is rarely more evident, especially in malnourished infants, and requires a few days of lactose-free feedings. Abundant literature conclusively shows that breastfeeding can and should always be continued throughout an episode of gastroenteritis, despite the high content of lactose in breast milk.

  • Food avoidance: Many people with lactose intolerance instinctively avoid products that contain lactose.



Physical examination may reveal the following:

  • Abdominal pain: Nonspecific, nonfocal abdominal pain and cramping are common and are sometimes associated with bloating and flatus. This pain may mildly increase with palpation. Focal abdominal pain significantly worsened by palpation, the presence of rebound tenderness, or guarding should alert the clinician to a more serious and possibly surgical GI diagnosis.

  • Borborygmi: A significant increase in peristaltic activity in the small bowel can cause an audible or palpable increase in bowel activity.



Causes include the following:

  • Lactose intolerance: This is caused by a low or absent activity of the enzyme lactase.

  • Adult-onset lactose intolerance

    • This deficiency results from an unusual mechanism that involves a developmentally regulated change of the lactase gene product, resulting in a reduced synthesis of the precursor protein.

    • Differences in the rate of gene transcription account for much of the differences in lactose intolerance observed among racial groups.

  • Low lactase activity in the small intestine: This allows undigested lactose to pass into the colon. In the colon, bacteria ferment the sugar to hydrogen gas and organic acids. The gas produces distention of the bowel, creating the sensation of bloating, cramping, and abdominal pain. Organic acids can be absorbed, but the quantity produced is rarely large enough to cause systemic symptoms or metabolic acidosis.