Digestive Problems
Diseases: Small Bowel: Lactose Intolerance
Lactose is a special type of sugar which occurs in dairy products. To be absorbed, the lactose needs to be split into its two component sugars (glucose and galactose). This digestion is brought about by enzymes (i.e. lactase) which lie in the microvilla of the lining of the intestine. When there is a deficiency of this enzyme, lactose cannot be broken down. Resulting diarrhea is due to fluid entering into the small intestine due to the osmotic affect of the undigested lactose, but also due to lactose passing to the colon where it is broken down by bacteria to organic acids and fermented. A significant amount of water can be lost into the intestine following the ingestion of a large lactose load.
Lactose intolerance is probably one of the most common genetic deficiencies and occurs in 5 to 10% of Caucasians of northwestern European ancestry, but in greater than 90% of people of African, Chinese or Mediterranean background. However, it is not always clinically significant as this depends on the amount of lactose that is ingested.
Some individuals can develop secondary lactose intolerance. This occurs when the intestinal mucosa is injured such as in celiac disease, Crohn's disease or even infections. The inflammation damages the cells that produce lactase.
The classic clinical features of lactase deficiency are diarrhea, bloating, and gas. Many patients are labeled with the diagnosis of "irritable bowel syndrome" before lactase deficiency is considered. Occasionally, patients may develop osteoporosis as they avoid all milk products and become calcium and vitamin D deficient.
An informal diagnosis of lactose intolerance could be made by asking the patient to avoid all milk products. Alleviation of symptoms can occur in a few days on a modified dairy free diet. A more formal way of diagnosing lactose intolerance is to perform a special breath test. During this test the patient ingests radioactively labeled lactose and is then asked to breathe into a bag which measures labeled hydrogen and methane (produced by the breakdown of lactose by colonic bacteria). If the patient is truly lactose intolerant they may develop significant symptoms during this test. Another way for assessing for lactase deficiency is to perform a blood test after lactose ingestion to measure blood sugar levels, which should rise if it is being digested and absorbed normally.
Treatment includes restriction of dietary lactose, prevention of dietary deficiencies (particularly calcium and vitamin D), and empiric use of lactase preparations which can be taken whenever a small amount of dairy product is eaten.