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Lactose intolerance

Last updated: November 25, 2020

Summary

Lactose intolerance is caused by the malabsorption of lactose. It may be genetically determined or due to a functional deficiency of the lactase enzyme in the epithelium of the small intestine. After consuming food or beverages containing lactose, affected individuals develop abdominal symptoms such as pain, diarrhea, and bloating. Lactose intolerance is diagnosed with a hydrogen breath test or lactose intolerance test. The condition may be managed well with lactase supplements or by avoiding lactose altogether.

Definition

Lactose intolerance is the inability to absorb lactose; , caused by lactase deficiency.

Epidemiology

  • Approximately 70% of the world's population is lactose intolerant.
  • Lactose intolerance is more common in certain regions, particularly Asia, parts of Africa, and South America, where up to 90% of the population is affected.
  • Prevalence increases with age.

References:[1][2][3]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

References:[4]

Pathophysiology

Lactase deficiency is a malabsorption disorder.

Clinical features

Symptoms occur about an hour to several hours following consumption of milk products. The intensity of symptoms correlates with the amount of lactose consumed. [4]

  • Diarrhea (often watery, bulky, and frothy)
  • Cramping abdominal pain (often periumbilical or in the lower abdomen)
  • Abdominal bloating, flatulence
  • Nausea

Symptoms vary widely as most patients have residual amounts of lactase.

Diagnostics

  • Stool analysis
  • Hydrogen breath test
    • The amount of hydrogen in the expired air increases after administering lactose in the fasting state.
    • Procedure
      • Fasting for 8–12 hours
      • Ingestion of lactose
      • Measurement of breath hydrogen levels at baseline and at 30‑minute intervals over 3 hours
      • Breath hydrogen levels > 20 ppm are considered diagnostic of lactose intolerance.
  • Lactose tolerance test: Following the administration of lactose, the normal rise in blood glucose levels is pathologically reduced (< 20 mg/dL over 2 hours) and symptoms appear (rarely used, as the test has low sensitivity and specificity)
  • Trial lactose‑free diet: to see if symptoms resolve
  • Biopsy of the small intestine: qualitative and quantitative assessment of lactase via endoscopic tissue biopsy (conclusive, but rarely used, as the test is more invasive than other tests).
    • Primary lactose intolerance: normal intestinal architecture
    • Secondary lactose intolerance
      • Mucosal damage (especially injured tips of intestinal villi)
      • Specific histopathological findings corresponding to the underlying condition (see “Etiology”)
  • Genetic test (if primary lactose malabsorption is suspected)

References:[4]

Differential diagnoses

References:[5]

The differential diagnoses listed here are not exhaustive.

Treatment

  • Avoid or reduce intake of milk products: lactose‑free or lactose‑reduced products have become more readily available
    • Many patients tolerate small amounts of milk (∼ 240 mL per day).
    • Use of alternative foods, such as soy‑based products
    • Awareness of lactose in processed foods or foods other than dairy products (e.g., bread, salad dressings)
  • Oral lactase supplements
    • Recommended when traveling or before consuming food or milk products containing lactose
    • A wide variety of nonstandardized over‑the‑counter lactase supplements are available
  • Treatment of the underlying condition in patients with secondary lactose intolerance

References:[4][5]

References

  1. Lactose Intolerance. https://ghr.nlm.nih.gov/condition/lactose-intolerance. Updated: April 4, 2017. Accessed: April 5, 2017.
  2. Lactose intolerance: Overview. https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072452/. Updated: June 17, 2015. Accessed: April 5, 2017.
  3. Suchy FJ, Brannon PM, Carpenter TO et al. Lactose Intolerance and Health. Annals of Internal Medicine. 2010; 152 (12): p.792-796.
  4. Heyman MB. Lactose intolerance in infants, children, and adolescents. Pediatrics. 2006; 118 (3): p.1279-1286. doi: 10.1542/peds.2006-1721 . | Open in Read by QxMD
  5. Swagerty DL Jr, Walling AD, Klein RM. Lactose intolerance. Am Fam Physician. 2002; 65 (9): p.1845-1851.
  6. Herold G. Internal Medicine. Herold G ; 2014
  7. Guandalini S. Pediatric Lactose Intolerance Clinical Presentation. Pediatric Lactose Intolerance Clinical Presentation. New York, NY: WebMD. http://emedicine.medscape.com/article/930971-clinical. Updated: July 17, 2015. Accessed: April 5, 2017.