Diarrhea, abdominal pain, and flatulence (gas) following ingestion of milk or products containing milk are common complaints in infants and children. Generally, the symptoms are lower in younger children and begins to increase around school age. European and white Americans have the lowest incidence of lactose intolerance. African, Hispanic, Asian and Native Americans have higher incidence.

Dr. P.F. Bass discusses lactose intolerance in a recent journal article in Contemporary Pediatrics. Lactose is a sugar in milk. It is digested by an enzyme called lactase. Lactase deficiency is defined as decreased lactase enzyme activity in the intestinal brush border. The breakdown enzyme is not being made and therefore the sugar lactose cannot be absorbed. Lactose malabsorption is the failure to absorb lactose in the small bowel. Lactose intolerance is the symptoms or the clinical syndrome when the individual cannot absorb lactose.

Normally about 25 percent of the sugar lactose is absorbed in the small intestine. In the colon the remainder of unabsorbed lactose in converted into fatty acids and hydrogen by the bacteria that live in the gut. This process in the colon can help some people absorb lactose when they are deficient of lactase. However, if the normal bacteria are upset by bacterial overgrowth from antibiotics, intestinal infections or other inflammatory gut processes such as celiac disease, there may be lactose malabsorption and all the symptoms that occur with that.

To make the diagnosis of lactose intolerance your doctor may put you or your child on a strict lactose-free diet for a two-week trial. If symptoms go away and lactose is reintroduced to the diet and symptoms come back, the diagnosis is made. There is also a simple, noninvasive test where the patient receives a lactose load and the breath is measured for hydrogen after blowing in a small bag.

Hidden sources of lactose include baked goods such as bread, breakfast cereal, soft drinks and processed meats. Reading food labels can identify hidden ingredients which contain lactose such as the following: butter, buttermilk, casein, cheese, curds, dry milk solids, malted milk, margarine, milk by products, nougat, sour cream, sweet cream, and whey.

A total lactose free diet is associated with lower calcium absorption and lower vitamin D. Most patients can tolerate one to two cups of milk without significant symptoms. Taking this amount over an entire day may be better tolerated. Yogurt and aged cheese may also be better tolerated. There are commercially available lactase enzyme preparations available as liquid or sprinkles. Lactaid may be taken daily by children ages 4 and older (bit.ly/ Lactaid-FAQs).

Your health care provider will encourage calcium rich foods and consider calcium supplements. Vitamin D levels should be monitored and supplements given when indicated.

Sally Robinson is a clinical professor of pediatrics at UTMB Children’s Hospital. This column isn’t intended to replace the advice of your child’s physician.