Lactose intolerance — an inability to tolerate dairy products — is one of the most common inherited con- ditions in the world, although the exact prevalence is unknown. Lactose intolerance that develops gradually, called late-onset or adult-onset lactose intolerance, is common in adults. Gastrointestinal disorders can also cause temporary or permanent lactose intolerance. Symptoms of lactose intolerance include gas, diarrhea and abdominal pain 30 minutes to 2 hours after eating dairy products.
The ability to digest lactose, the milk sugar in dairy products, requires the presence of an enzyme called lactase. Produced by cells in the lining of the small in- testine, lactase breaks lactose down into the sugars that can be absorbed into the bloodstream.
Lactase production decreases, starting after age 2 and continuing through adolescence. Most people can tolerate
up to 12 grams of lactose, about the amount found in a 1-cup serving of milk,at a time without symptoms.
Acquired or genetic conditions, such as irritable bowel syndrome, Crohn disease and HIV infection, can cause secondary lactose intolerance in adults. Destruc- tion of the cells that produce lactase because of damage to the lining of the small intes- tine cause lactose intolerance with these conditions. Alcohol can also inhibit lactase production and cause secondary lactose intolerance in adults.
Lactose intolerance can cause temporary problems if you’ve had a viral or bacterial infection of the gastrointestinal tract. In these cases, the infection temporarily disrupts the function of the lactase-producing cells. Lactase is the first enzyme affected and the last to return to normal production.
For many older adults, the production of lactase may decrease with age, causing an increase in lactose intolerance even in people who haven’t previously had a problem digesting lactose. Lactose intolerance is more common in individuals age 74 and older compared to those under age 65, the textbook “Geriatric Gastroenterology” reports. However, the National Institutes of Health points out that little evidence suggests a decrease in lactose production as people age. More research on this topic is needed.