'Lactose intolerance' more common than true milk allergy

Published: Sunday, October 25, 1998

Q: I have always enjoyed milk, and as a vegetarian I eat quite a bit of cheese and yogurt as well. Over the years I have been increasingly bothered by gas after eating. A friend has suggested that I may be allergic to milk. Does this sound likely? V.W., Cincinnati, Ohio

A: True milk allergy is rare. Milk allergy is an abnormal immune reaction to milk and can cause digestive symptoms as well as rashes, hives, swelling of the lips, tongue or throat and breathing difficulties. It typically begins in infancy and is usually outgrown by age three.

A more common problem is ''lactose intolerance,'' a condition caused by difficulty in digesting milk sugar (lactose).

Lactose intolerance results in symptoms such as bloating, diarrhea, flatulence (intestinal gas) and abdominal cramps that usually begin one-half to two hours after consuming foods containing lactose.

Lactose is the major sugar present in both cow's milk and human milk. In order to utilize lactose, it must be broken down into its smaller component sugars, galactose and glucose. Lactase, an enzyme produced in the small intestine, is required for this breakdown to occur.

Babies ordinarily produce large amounts of lactase, enabling them to utilize nature's primary source of infant nutrition, milk. High lactase levels do not usually persist; beginning as early as two years of age, lactase production may begin to decline.

This results in what is called ''primary hypolactasia'' or ''lactase nonpersistence'' and is more appropriately considered a normal process of maturation rather than a disorder.

Nearly 75 percent of adults worldwide are lactase nonpersistent. Decline in lactase production is genetically programmed and varies considerably between ethnic groups.

When lactase levels are insufficient to break down the amount of lactose consumed, some lactose passes intact to the large intestine (colon), where it is digested by bacteria.

This process produces gases that are eliminated through further bacterial activity or absorption into the bloodstream, but in some people this does not occur rapidly enough to avoid symptoms such as bloating and gas.

Colonic lactose not digested by bacteria increases water retention in the colon and may also lead to diarrhea.

Reduced lactase levels do not always cause symptoms even when lactose is consumed.

In those who do develop symptoms, lactose intolerance is not an all-or-nothing proposition. The severity of symptoms, as well as the amount of lactose consumed before symptoms arise, varies from individual to individual.

There is concern that people may be too quick to blame their digestive symptoms on lactose intolerance and unnecessarily reduce their dairy intake, when in fact their symptoms may arise from other causes or simply represent normal sensations.

A University of Minnesota study found 9 of 30 adults who thought they were severely lactose intolerant were not low in lactase and were able to digest lactose with no problem. The results of this study, lead by Dr. Fabrizis Suarez appears in the July 6, 1995, issue of The New England Journal of Medicine.

Poor lactose digestion (maldigestion) can be confirmed through a breath test that checks for hydrogen produced during bacterial fermentation of lactose, evidence that undigested lactose has reached the colon.

Another test measures blood glucose levels which, after consuming lactose, rise only if sufficient lactase is available for lactose digestion.

In the United States over 70 percent of calcium is consumed as dairy products. Calcium is important in preventing osteoporosis, hypertension and possibly some cancers.

Most Americans fall short of consuming the daily requirements for this mineral, and restricting dairy intake makes adequate calcium intake more difficult.

In addition to dairy, calcium is available in some green vegetables, such as broccoli, kale and turnip greens; fish such as salmon and sardines; tofu; and molasses. If necessary, calcium can be obtained by taking supplements.

Several studies have found that most lactose-intolerant individuals can consume at least one cup or two cups of milk per day without problems.

Most people with lactose intolerance may continue to enjoy dairy products in moderation by following a few simple steps:

1. Drink milk with meals rather than on an empty stomach; stagger consumption throughout the day.

2. Consume dairy products that are naturally low in lactose, such as hard cheeses (most of which are nearly lactose-free).

3. Eat ''live culture'' yogurt that, although high in lactose, also contains lactase-producing organisms.

4. Try switching the type of milk you drink. Some people handle chocolate milk better than plain milk, and whole milk better than versions lower in fat.

5. Determine your level of tolerance and consume dairy products regularly. Eating dairy periodically may be more likely to cause symptoms than regular consumption. Regular intake does not raise lactase levels, but appears to increase the rate at which bacteria can digest lactose.

6. Use digestive aids if needed. Aids that contain enzymes to digest lactose can be taken in tablet form prior to meals. There is also a liquid enzyme that can be added to milk. Pretreated milk is also available.

7. Look for hidden lactose. Milk is the only natural source of lactose, but lactose is often added to processed foods such as baked goods, cereals, lunch meats, salad dressings, soups and candy; and it may even be present in some medications or products labeled nondairy. Check labels for terms such as milk solids, whey, curd and sodium caseinate.

Before attributing recurrent digestive symptoms to lactose intolerance, it is prudent to consult a physician to rule out other possible causes, such as irritable-bowel syndrome or, even though unlikely, milk allergy.

Although it can be a source of considerable discomfort, lactose intolerance in itself is not dangerous to adults.

It can be managed using a trial-and-error approach using comfort as a guide in determining which dietary modifications are appropriate.

A free booklet entitled ''Lactose Intolerance'' (NIH Publication No. 94-2751) is available by writing the National Digestive Diseases Information Clearing House at 2 Information Way, Bethesda, Md. 20892-3570, or by visiting their Web site at http://www.niddk.nih.gov.

Send your questions to: The Medical Adviser, c/o Medical Information Foundation, 2420 Sand Hill Road, Suite 101, Menlo Park, Calif. 94025. For a fee, the Medical Information Foundation will conduct a personalized medical literature search. For information, call (800) 999-1999.

