Basics
Description
- Lactose intolerance is defined as the inability to digest the ingested disaccharide lactose secondary to a deficiency of the intrinsic enzyme lactase, resulting in clinical symptoms.
- Lactose is a disaccharide composed of glucose and galactose.
- Lactose is important as a source of energy; it is the major carbohydrate in human and other mammalian milks; promotes the absorption of calcium, phosphorus, and iron; and has a probiotic effect on the gut flora.
- Four types of lactase deficiency
- Congenital lactase deficiency
- Extremely rare
- Presents during the newborn period
- Will cause severe diarrhea and failure to thrive and risk the newborn 's life
- Primary lactase deficiency (adult-type hypolactasia)
- Due to relative or absolute absence of lactase
- Develops during childhood at different ages in different racial groups
- Most common cause of lactose intolerance
- Secondary lactase deficiency
- Results from small bowel injury (acute gastroenteritis, persistent diarrhea, small bowel bacterial overgrowth, chemotherapy)
- Can present at any age, more common in infancy
- Developmental lactase deficiency
- A relative lactase deficiency observed in premature infants <34 weeks ' gestation
Epidemiology
Prevalence
- ~70% of the world 's population is prone to primary lactase deficiency.
- The prevalence of primary lactase deficiency in northern Europeans, who have a diet rich in dairy, is 2%.
- In Hispanic populations, the prevalence of primary lactase deficiency is 50 " “80%.
- In Ashkenazi Jewish and African American populations, the prevalence is 60 " “80%.
- In Asian populations, the prevalence of primary lactase deficiency is nearly 100%.
- Nearly 20% of children <5 years from Hispanic, Asian, or African American descent have lactase deficiency and lactose malabsorption.
- Caucasian children usually do not develop symptoms until after 5 years of age.
Risk Factors
Genetics
- Posttranslational regulatory mechanisms in primary lactase deficiency or adult-type hypolactasia
- Correlation between the genetic polymorphism of mRNA and persistence of lactase activity with early loss at 1 " “2 years in Thai children and late loss at 10 " “20 years in Finnish children
Pathophysiology
- Symptoms depend on the amount of lactose ingested.
- Malabsorbed lactose creates an osmotic load that draws fluid and electrolytes into the bowel lumen, leading to an osmotic diarrhea.
- Nonabsorbed lactose acts as a substrate for intestinal bacteria.
- In the colon, bacteria metabolize lactose, producing volatile fatty acids and gases leading to flatulence, bowel distension, pain, and low pH.
Diagnosis
History
- Classic symptoms include bloating, gaseousness, colicky abdominal pain, and diarrhea after digestion of lactose-containing meal.
- Dietary intake history provides important information.
- Association with milk ingestion may not be evident.
- Symptoms vary in severity with dose of lactose ingested.
- Detailed history of symptoms:
- Blood or mucus in the stools, weight loss, poor growth, fat malabsorption, or any extraintestinal symptoms strongly suggest different causes.
Physical Exam
- Height and weight should be measured and plotted against age-appropriate norms; any deviation should not be attributed to lactose intolerance alone.
- Abdomen percussion: Abdomen may be distended and tympanitic.
- Blood in the stool must be further evaluated as lactose intolerance does not cause bleeding.
Diagnostic Tests & Interpretation
Lab
- Stool-reducing substances and fecal acidity
- A pH <6.0 or reducing substances >0.5% should be interpreted as positive results.
- Positive results indicate malabsorption of carbohydrates.
- Lactose hydrogen breath test
- Noninvasive and highly sensitive
- A rise of breath H2 concentration of ≥20 ppm over baseline has been shown to correlate with enzyme deficiency.
- However, there is poor association between symptoms of lactose intolerance and breath H2 excretion, which underscores the need for caution in the interpretation of the clinical significance of the breath hydrogen test.
- False-positive test results can occur if inadequate fasting before the test, rapid intestinal transit, toothpaste, smoking, and bacterial overgrowth.
- False-negative results occur with diarrhea, hyperventilation, recent antibiotic exposure, and delayed gastric emptying. In addition, up to 10% of the population is colonized with bacteria unable to produce hydrogen, which can lead to a falsely negative result.
- Lactase activity measurement from endoscopically obtained duodenal tissue biopsies (invasive and expensive)
Pathologic Findings
The small bowel intestinal histology will often be normal in primary lactase deficiency (unless the reason is insult/damage to the small bowel mucosa). ‚
Differential Diagnosis
- Infection
- Viral and bacterial infections can cause secondary lactose intolerance due to villous injury.
- Most common pathogen is rotavirus.
- Parasitic infections can mimic lactose intolerance (giardiasis).
- Inflammatory conditions
- Small intestinal Crohn disease
- Celiac disease
- Congenital
- Other carbohydrate enzyme deficiencies can mimic lactose intolerance. These include sucrase " “isomaltase or glucose " “galactose malabsorption.
- Cystic fibrosis
- Shwachman-Diamond syndrome (SDS): Primary features include the following:
- Bone marrow insufficiency
- Pancreatic insufficiency
- Skeletal abnormalities
- Short stature
- Allergic/immune
- Food protein allergies
- Oral medications containing lactose: common in tablets
Treatment
Medication
- Oral lactase replacement capsules
- Calcium supplements to ensure daily recommended intake levels despite dairy restriction
Additional Treatment
General Measures
- Removal of lactose from the diet is effective in eliminating symptoms.
- However, it is important to recognize that a milk-free diet is associated with calcium deficiency.
- Predigestion of lactose can be done by the addition of commercially available enzyme supplementation (extrinsic lactase). Multiple products are available over the counter. Liquid preparations, capsules, and chewable tablets can be obtained.
- Acquired deficiencies, particularly those associated with infection, may resolve over time or with specific treatment. Many patients with lactose intolerance do not recover the ability to digest lactose.
- Supplemental probiotics may improve symptoms of lactose intolerance.
Ongoing Care
Diet
- Lactose-free formula, lactase-containing milk
- Cow milk substitutes (e.g., rice or soy milk)
- Yogurt and aged cheeses, which generally have smaller content of lactose.
Prognosis
- Prognosis of lactase deficiency and clinical intolerance is excellent with lactose reduction or elimination as well as enzyme replacements are possible.
- Lactose intolerance secondary to disease processes should be recognized and treated appropriately.
Additional Reading
- Heyman ‚ MB, Committee on Nutrition. Lactose intolerance in infants, children, and adolescents. Pediatrics. 2006;118(3):1279 " “1286. ‚ [View Abstract]
- Krawczyk ‚ M, Wolska ‚ M, Schwartz ‚ S, et al. Concordance of genetic and breath tests for lactose intolerance in a tertiary referral centre. J Gastrointestin Liver Dis. 2008;17(2):135 " “139. ‚ [View Abstract]
- Law ‚ D, Conklin ‚ J, Pimentel ‚ M. Lactose intolerance and the role of the lactose breath test. Am J Gastroenterol. 2010;105(8):1726 " “1728. ‚ [View Abstract]
- Levitt ‚ M, Wilt ‚ T, Shaukat ‚ A. Clinical implications of lactose malabsorption versus lactose intolerance. J Clin Gastroenterol. 2013;47(6):471 " “80. ‚ [View Abstract]
- Mattar ‚ R, de Campos Mazo ‚ DF, Carrilho ‚ FJ. Lactose intolerance: diagnosis, genetic, and clinical factors. Clin Exp Gastroenterol. 2012;5:113 " “121. ‚ [View Abstract]
- Usai Satta ‚ P, Congia ‚ M, Schirru ‚ E, et al. Genetic testing is ready to change the diagnostic scenario of lactose malabsorption. Gut. 2008;57(1):137 " “138. ‚ [View Abstract]
Codes
ICD09
- 271.3 Intestinal disaccharidase deficiencies and disaccharide malabsorption
ICD10
- E73.9 Lactose intolerance, unspecified
- E73.0 Congenital lactase deficiency
- E73.8 Other lactose intolerance
- E73.1 Secondary lactase deficiency
SNOMED
- 267425008 lactose intolerance (disorder)
- 5388008 Congenital lactase deficiency
- 190751001 Primary lactose intolerance
- 60414003 Acquired lactase deficiency
FAQ
- Q: When is the usual time for presentation of lactose intolerance?
- A: In whites, the age of presentation is after 5 years of age. In African Americans, 2 " “3-year-old children may present with clinical signs and symptoms. The differential diagnosis must distinguish primary from secondary causes.
- Q: Does lactose intolerance prevent a child from ever eating lactose?
- A: No. The patient can take smaller amounts of lactose in the diet or have the enzyme supplemented.
- Q: Does this problem ever get better?
- A: No. It is a lifelong problem, but seems to become less symptomatic for adults, in light of their individual desire to tolerate symptoms. Secondary lactose intolerance may improve with time or treatment of the primary disorder.