Lactose Intolerance

Lactose Intolerance

Definition

Lactose intolerance occurs when a person cannot digest lactose, a sugar

found in milk and other dairy products. Lactose intolerance develops

when lactase, an enzyme that is needed to break down milk sugar into

simpler sugars, is less available or absent.

Description

Lactose intolerance is a very common chronic digestive disorder in which

a person

breaks down lactose, or milk sugar, into two simpler sugars that the body

can use. A person can have a lactase deficiency without having the symptoms

of lactose intolerance.

Lactose intolerance is not the same as being allergic to cow

An allergy to cow

lactose intolerance has to do with the process of digestion.

Lactose intolerance may be caused by any of three different factors. One

is normal aging. As people get older, their small intestine produces lower

amounts of lactase. After the lactase production drops below a certain point,

the person may experience the symptoms of lactose intolerance.

A second cause of lactose intolerance is diseases of the intestines or

surgical procedures in which part of the small intestine is removed. These

disorders or operations may affect the part of the

small intestine that secretes lactase. The third

cause of lactose intolerance is genetic. A few

people inherit lactose intolerance from both

parents and are affected from birth.

The symptoms of lactose intolerance usually

begin within half an hour to two hours after

drinking milk or eating a meal high in dairy products.

The person typically experiences diarrhea,

which is the most common symptom of lactose

intolerance, along with a gassy, bloated feeling,

abdominal cramps, and possibly nausea. The

severity of the symptoms is not necessarily related

to the amount of milk or dairy products that

were consumed but rather to the person

ethnicity, and the speed of his or her digestive

processes.

’s age,

Demographics

In most cases, lactose intolerance is part of the

normal human developmental process. Most

mammals stop producing lactase after they are

weaned because they are eating solid food instead of drinking milk

from the mother. Humans begin to slow down the production of lactase

some time around age three to five years; thus most human adults

are at some risk of developing lactose intolerance.

It is noteworthy, however, that the levels of lactose intolerance

vary quite widely among different ethnic groups. In some groups,

almost 100 percent of the adult population may be lactose intolerant.

In the United States and Canada, lactose intolerance is estimated to

affect between 20 and 60 percent of the adult population. In terms

of specific ethnic groups, people of Dutch, Swedish, German, or

other northern European descent have low rates of lactose intolerance

(about 5 percent); persons of southern European ancestry have rates

between 18 and 25 percent; African Americans have a rate around

45 percent; persons from Japan or southeastern Asia have rates above

95 percent; and Native Americans are almost 100 percent lactose

intolerant.

One theory that has been proposed to explain these differences is the

long-standing differences among human societies in milk consumption

after childhood. In Asia and Africa, children were rarely given milk after

being weaned; in these societies, lactase production generally falls by

90 percent by the time the child is four years old. In societies in which

milk consumption continues into adult life, however, a mutation on

chromosome 2 that bypasses the normal shutdown of lactase production

became widespread in the population. Thus members of these groups

can continue to consume milk and dairy products throughout their adult

lives. Some researchers have traced the mutation back as far as 4500

BCE

in both Sweden and the Middle East.

Causes and Symptoms

Lactose intolerance results from a drop in or disruption of the production

of lactase in the small intestine. Lactase is produced by specialized cells in

the membrane that lines the villi, which are small finger-like projections

on the walls of the small intestine. The production of the enzyme may

drop at a certain age or because a disease or radiation treatment for cancer

has damaged the villi of the small intestine.

The symptoms of lactose intolerance are diarrhea, bloating, nausea,

and a gassy feeling within thirty minutes to two hours following a meal

high in dairy products. They do

digestive tract, or weight loss in adults. People who have these symptoms

should be checked by their doctors for other disorders of the intestines.

not include fever, bleeding from the

Diagnosis

Diagnosis of lactose intolerance is based on a patient

a detailed history of the patient

Many people underestimate the amount of milk or products containing

lactose that they consume; they may not think of yogurt or ice cream, for

example, as milk products. After getting a complete picture of the

patient

for a week or so in order to see whether the symptoms improve. If they

do, further testing may be unnecessary.

There are three tests that can be used, one of which is generally given

only to infants and small children. It is a test that measures the acidity of

the child

and forms an acid that can be measured in the stool sample.

The most common diagnostic test used in adults is the hydrogen

breath test. The patient is asked to drink a liquid containing a high level

of lactose. The doctor then measures the amount of hydrogen in the

breath at certain intervals. Undigested lactose reaches the colon and ferments,

causing hydrogen and other gases to be released, absorbed by the

intestines, and eventually exhaled. Large amounts of exhaled hydrogen

indicate that the patient

that the patient is probably lactose intolerant.

The third type of diagnostic test involves taking a small sample of

tissue from the lining of the small intestine and measuring the amount

of lactase present in the tissue sample. This type of test requires a specialized

laboratory to evaluate the results, however, and is rarely used outside

clinical research.

’s body is not digesting lactose completely and

Treatment

There are several treatment options for lactose intolerance:

•

This change in diet usually requires careful reading of labels on

other foods because many processed foods contain milk or milk

solids (see sidebar). In addition, some drug manufacturers use lactose

as a binding substance to carry the active ingredient in the

medication. The patient may need to check with the doctor or

pharmacist about any prescription medications they may be using

to see if the drugs were formulated with lactose.

Completely eliminating milk and dairy products from the diet.

•

reintroducing small amounts of them. Some people can tolerate

small amounts of yogurt or milk after avoiding them

completely for a few weeks.

Eliminating dairy products from the diet for a time and then gradually

•

products and other plant-based substitutes for milk.

Using specially manufactured lactose-free milk products or soy

•

Lactaid, DairyEase, and Lactogest can be purchased without a

prescription.

People who are concerned about the risk of osteoporosis (brittle bones)

can take calcium supplements to keep their bones strong rather than getting

their calcium from milk. Patients should ask their doctors how much

calcium they should be getting from other sources. Most adults should not

take more than 1,200

Prognosis

Most people recover completely by removing milk products from the

diet or by substituting reduced-lactose or lactose-free dairy products for

those that contain lactose.

Prevention

There is no way to prevent congenital or adult-onset lactose intolerance.

The Future

Lactose intolerance is not a life-threatening condition. Most people can

manage quite well by using milk substitutes, watching the amount of

milk and other dairy products that they consume, or by taking overthe-

counter lactase supplements. There are also a number of cookbooks

with lactose-free recipes or recipes that use milk substitutes.

SEE ALSO

Osteoporosis

Celiac disease; Crohn disease; Irritable bowel syndrome;

For more information

BOOKS

Dobler, Merri Lou.

Dietetic Association, 2003.

Goldberg, Phyllis Z.

Eating Well without Dairy Products

Lactose Intolerance Nutrition Guide. Chicago: AmericanHow to Tolerate Lactose Intolerance: Recipes and a Guide for. Springfield, IL: Charles C. Thomas, 1998.

PERIODICALS

Brody, Jane.

York Times

com/gst/fullpage.html?res=9C03E3D91E3BF935A1575AC0A9669C

8B63&sec=&spon=&pagewanted=all (accessed May 3, 2008).

WEB SITES

International Foundation for Functional Gastrointestinal Disorders (IFFGD).

Lactose Intolerance: Definition, Symptoms and Treatment

PDF format (free download) at http://www.iffgd.org/store/viewproduct/122

(updated September 2007; accessed May 4, 2008).

Mayo Clinic.

com/health/lactose-intolerance/DS00530 (updated February 16, 2008;

accessed May 4, 2008).

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

. Available online inLactose Intolerance. Available online at http://www.mayoclinic.

Lactose Intolerance

nih.gov/ddiseases/pubs/lactoseintolerance/lactoseintolerance.pdf (updated

March 2006; accessed May 4, 2008).

TeensHealth.

teen/nutrition/diets/lactose_intolerance.html (updated September 2006;

accessed May 4, 2008).

 WORDS TO KNOW
Chronic: Recurrent or long-term
Congenital: Present from birth.
Lactase: An enzyme that breaks down lactose
into simpler sugars during the process of
digestion.
Lactose: A complex sugar found in milk and other
dairy products. It is sometimes called milk sugar.
Villi (singular, villus): Small finger-like projections
along the walls of the small intestine that
increase the surface area of the intestinal wall.. Available online in PDF format at http://digestive.niddk.Lactose Intolerance. Available online at http://www.kidshealth.org/“Personal Health: Debate over Milk: Time to Look at Facts.” New, September 26, 2000. Available online at http://query.nytimes.Taking dietary supplements that contain lactase. Products like–1,500 milligrams of calcium per day.’s history, particularly’s consumption of dairy products.’s diet, the doctor will usually suggest cutting out dairy products’s stool sample. Undigested lactose ferments inside the intestine’s intestinal tract lacks the ability to make lactase, an enzyme that’s milk.’s milk concerns a person’s immune system, whereas