DEAR MAYO CLINIC:

I used to be able to eat and drink dairy products without a problem, but lately they make me feel gassy and bloated. Does this mean I'm lactose intolerant? Would that mean giving up all dairy? I'm 42 and have never had any allergies.

ANSWER:

If you regularly develop digestive symptoms shortly after consuming milk or other dairy products, you may indeed have lactose intolerance.

Lactose intolerance is the inability to fully digest lactose, the sugar that's in milk and other milk products. This is caused by a deficiency of lactase, an enzyme that's responsible for breaking lactose into two simpler sugars -- glucose and galactose -- which can be absorbed into your bloodstream. When levels of the lactase enzyme are too low, eating something like a bowl of ice cream or a slice of cheesy pizza can cause a number of signs and symptoms, including abdominal cramps, bloating, gas, diarrhea and nausea.

However, to confirm the diagnosis, your doctor may suggest that you take a hydrogen breath test. This test requires you to drink a lactose-loaded beverage and then have your breath analyzed over a 90-minute period. When lactose isn't properly digested, hydrogen levels typically go up in the breath.

Sometimes, people mistake lactose intolerance for a milk allergy. But a milk allergy is caused by an immune system response to one or more milk proteins and usually appears very early in life. Lactose intolerance, on the other hand, occurs more often in adulthood.

Your body typically produces plenty of the lactase enzyme at birth and during early childhood. In fact, it's rare for babies to be born with lactose intolerance. However, as you get older, you naturally start to lose some of the enzyme, or stop producing as much of it. This decline can lead to symptoms of lactose intolerance.

Another factor that can make you more prone to lactose intolerance is your ethnic background. Research has shown that being black, Asian, Hispanic or American Indian increases your risk. Having certain digestive disorders -- such as celiac disease or Crohn's disease -- also can make you more likely to develop lactose intolerance as a secondary condition. That's because these problems can cause damage to your small intestine, where the lactase enzyme is produced.

The symptoms of lactose intolerance can be controlled through diet. At first, it may be recommended that you eliminate all dairy products to see if your symptoms resolve. However, most people can tolerate small amounts of lactose, so it's usually not necessary to completely avoid dairy products from then on.

If you haven't had any dairy products in a while, you may want to gradually reintroduce them into your diet. Research shows that most people can tolerate 12 grams of lactose at a time -- the equivalent of 1 cup of milk. Some dairy products, such as yogurt and hard cheeses, contain less concentrated amounts of lactose, which could make them easier to digest in small amounts. You may also be able to lessen symptoms of lactose intolerance by consuming dairy products along with a meal or other foods that don't contain lactose.

Many stores also carry lactose-free and lactose-reduced milk and other products. I've recommended them as an alternative for some people, but they may not be helpful in everyone. This also applies to lactase enzyme drops or pills taken by mouth; some people find them beneficial, but they haven't been well studied.

A big concern with restricting dairy products is that you won't get enough calcium and vitamin D in your diet. To make sure you're getting adequate amounts of these nutrients, talk with your doctor about your diet and whether taking supplements would be a good option for you.

Jean Fox, M.D., Gastroenterology, Mayo Clinic, Rochester, Minn.

Medical Edge from Mayo Clinic is an educational resource and doesn't replace regular medical care.

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