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Summary Article: Lactose Intolerance
From Encyclopedia of Global Health

Lactose intolerance is the inability of a person to digest lactose, the predominant sugar in dairy products. It affects people by causing gastrointestinal discomfort, and can make dietary freedom difficult for those afflicted. Lactose intolerance can be seen at birth (congenital), to develop on its own over time (primarily), or due to secondary afflictions than injure the intestinal lining.

The incidence varies according to race. For primary lactose intolerance, about 75 to 90 percent of Native Americans, Blacks, Latinos, Asians, Mediterraneans, and Jews can be affected. On the other end, only 5 percent of northern and central European descendants are affected. This is thought to be due to a genetic mutation leading to a dominant gene for lactase persistence. For secondary lactose intolerance, it can occur at any age, and about 50 percent of infants with diarrhea will have it.

There are many causes of lactose intolerance. In primary lactose intolerance, the amount of lactase enzyme normally declines gradually after weaning from breastfeeding. This is common in most land mammals and the loss is permanent. The diseases causing secondary lactose intolerance include rotavirus, giardia and other parasitic infections, inflammatory bowel disease, celiac disease, cystic fibrosis, and AIDS. Other medical treatment induced causes include chemotherapy, radiation injury, and bowel surgery. The length of time of secondary lactose intolerance persists depends on the causative factor.

Lactose is normally broken down in the small intestine by the enzyme lactase into glucose and galactose. When lactose remains undigested and unabsorbed in the colon, it attracts water which remains in the gut and causes a laxative-like effect. Signs and symptoms of lactose intolerance include bloating, cramping, abdominal pain, diarrhea, flatulence, vomiting, and malnutrition. The amount of lactose consumed is not necessarily related to the severity of the symptoms. People of different ages and races will have varying severities of illness when consuming the same amount of lactose.

Diagnosis of lactose intolerance can be done through multiple routes. There are various laboratory tests, as well as evaluating symptomatic response to ingestion of lactose containing products. (1) Stool acidity test: Stools will have low pH because undigested lactose ferments into lactic acid. Stool specimens must be fresh and processed immediately. (2) Lactose breath hydrogen test: Undigested lactose leads to the production of hydrogen in the gut. This is usually positive in 90 percent of patients with the condition when large doses of lactose are consumed. False-negative results may occur when the gut lacks its normal bacterial flora. Enemas and recent antibiotic use can contribute to this. Other factors such as aspirin use, smoking, and exercise may increase the hydrogen secretion and lead to false-positive results. (3) Lactose tolerance test: Normally, blood glucose levels should rise after digestion of lactose, thus in a lactose-intolerant individual who cannot digest lactose, there would be no obvious rise in blood glucose. (4) There are no diagnostic imaging studies to diagnose the condition, but biopsy of the small bowel may show enzyme deficiency. However, this is invasive and difficult to do. (5) A patient may consume lactose-free dairy products to determine if the symptoms are truly lactose intolerance or a possibly allergy to dairy products.

Treatment for lactose intolerance consists primarily of decreasing lactose consumption. Fermented dairy products are better tolerated as well as whole milk. Having milk with other foods may also reduce symptoms. Substitute milk with lactose-free milk, soy milk, or rice milk. Lactase supplementation through pills or solution added to milk or taken before dairy consumption may reduce symptoms. Treatment of lactose intolerance should also include treatment of the underlying causes of secondary lactose intolerance. Additionally, supplementation with calcium is important whether through ingesting other calcium-rich foods or tablets. Women may need about 1,500 mg per day and men will need at least 1,000mg per day. Dietary sources of calcium include tofu, sardines, oysters, collard greens, and many others.

People with lactose intolerance can make dietary alterations that will allow them to live life with less gastrointestinal discomfort.

  • Allergy; Diarrhea; Gastroenterology.

  • American Gastroenterological Association, Web-based patient center, Lactose Intolerance, (cited July 2007).
  • R. Alexander Rusynyk; Christopher D. Still, “Lactose Intolerance,” Journal of the American Osteopathic Association (v.101/4, Supplement, 2001).
  • Daniel L. Swagerty; Anne D. Walling; Robert M. KleinLactose Intolerance,” American Family Physician (v.64/9, 2002).
  • Kelli Glaser, D.O.
    Independent Scholar
    Copyright © 2008 by SAGE Publications, Inc.

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