LACTOSE INTOLERANCE

What Is Lactose Intolerance? Lactose intolerance is an inability to digest milk sugar due to a specific deficiency of the enzyme lactase, and not, as commonly believed, a "milk allergy." In normal individuals, food sugars are broken down into smaller molecules by chemicals called enzymes in the small intestine. Lactose, the sugar found in milk and dairy products, is normally processed to its two constituent sugars (glucose and galactose) by lactase, an enzyme found in the wall of the small intestine. Lactose intolerant individuals have insufficient amounts of, if any, lactase. Therefore, lactose remains unprocessed in the intestine, and draws in excess water, leading to diarrhea. It is then fermented by intestinal bacteria, producing gas, bloating, and acidic stools.

What Causes Lactose Intolerance? Primary lactose intolerance, a hereditary deficiency, appears most often in older children and young adults. This is the norm rather than the exception in the majority of ethnic groups worldwide. Although fewer than 20% of adults of Western European origin are lactase deficient, over 75% of all other adults lack the enzyme, including up to 90% of Orientals. Secondary lactose intolerance is a condition of lactase deficiency due to gastro-intestinal infection, celiac disease (sprue), or inflammatory bowel disease. In these patients, parts of the lining of the intestine containing lactase have been damaged by disease, and thus less lactase is available. This is the most common form of lactose intolerance in infants.

What Are The Signs And Symptoms Of Lactose Intolerance? Regardless of whether the enzyme deficiency is primary or secondary, the signs and symptoms are the same. Infants with lactase deficiency will have diarrhea and fail to gain weight. Adults have bloating, flatus, nausea, diarrhea and abdominal cramping following ingestion of dairy products.

With What Might Lactose Intolerance Be Confused? Until a clear link is established between a patient's symptoms and the ingestion of dairy products, lactase deficiency might be confused with another enzyme deficiency or, more probably, with irritable bowel syndrome, a bowel motility disorder with the symptoms of abdominal pain, bloating, constipation and diarrhea. Lactase deficiency and irritable bowel syndrome are equally prevalent in North America, and the presence of one does not rule out the other.

How Is Lactase Deficiency Diagnosed? Often, specific diagnostic tests are not required as a trial period of dairy product avoidance may result in cessation of symptoms. Stool samples may be requested, and if found to be acidic, the next step is a lactose tolerance test, which is positive for lactase deficiency if the oral dose of lactose results in discomfort and diarrhea within half an hour, and blood sugar does not rise. (Because the lactose has not been digested, blood sugar is not elevated by ingestion of milk products.) An alternative test is the hydrogen breath test, in which hydrogen produced by lactose-fermenting bacteria can be detected on the patient's breath after a dose of lactose. Finally, an intestinal biopsy may be performed; by removing a small sample of intestinal tissue, the presence of the lactase enzyme can be directly determined.

How Is Lactose Intolerance Treated? Approximately 70% of patients find relief by eliminating milk products from their diet. Alternatives to complete avoidance of dairy foods are the use of lactose-free milk, available in most supermarkets, and over-the-counter preparations of the enzyme lactase, which act in much the same way as the naturally-occurring enzyme. The remaining 30% of patients may not respond to such simple measures due to an underlying irritable bowel syndrome. Currently, research is underway in the area of gene therapy for lactose intolerance. In the future, individuals lacking the gene for lactase could have the gene artificially added to their genetic make-up and thus produce the enzyme.

What Are The Complications Of Lactose Intolerance? Dairy foods are by far the best dietary source of calcium. Therefore, individuals on a milk-free diet are at risk of calcium deficiency and its consequences, namely, osteoporosis and osteopenia, both disorders of lowered bone mineral density and susceptibility to fractures. As a result, lactose-intolerant patients with limited or no dairy intake should have their bone mineral density (BMD) regularly monitored.