Lactose intolerance is the inability to digest significant amounts of lactose, which is the predominant sugar of milk. Close to 50 million American adults are lactose intolerant. Certain ethnic and racial populations are more widely affected than others. As many as 75 percent of all African-American, Jewish, Native American, and Mexican-American adults, and 90 percent of Asian-American adults are lactose intolerant. The condition is least common among people of northern European descent.
What Causes Lactose Intolerance?
Lactose intolerance results from a shortage of the enzyme lactase, which is normally produced by the cells that line the small intestine. Lactase breaks down milk sugar into simpler forms that can then be absorbed into the blood stream. When there is not enough lactase to digest the amount of lactose consumed, the results, although not usually dangerous, may be very distressing.
Common symptoms include nausea, cramps, bloating, gas, and diarrhea, which begin about 30 minutes to two hours after eating or drinking foods containing lactose. Many people who have never been diagnosed as lactose intolerant or "lactase deficient" may notice that milk and other dairy products cause problems that donít occur when eating other foods. The severity of symptoms varies depending on the amount of lactose each individual can tolerate.
Some causes of lactose intolerance are well known. For instance, certain digestive diseases and injuries to the small intestine can reduce the amount of enzymes produced. In rare cases, children are born without the ability to produce lactase. For most people, though, lactase deficiency is a condition that develops naturally, over time. After about the age of two years, the body begins to produce less lactase. The reasons for this are unclear and still under study. However, symptoms may occur years after childhood.
What Diagnostic Tests are Used to Detect Lactose Intolerance?
The most common tests used to measure the absorption of lactose in the digestive system are the lactose intolerance test, the hydrogen breath test, and the stool acidity test. A doctor can tell you where to go for these tests, which are performed on an outpatient basis at a hospital or clinic. A clinical response to lactose restriction may also be sufficient, at times, to make the diagnosis.
The lactose tolerance test can be given to older children as well as adults. Before the test, patients fast (do not eat), and blood is drawn to measure the fasting blood glucose (blood sugar) level. Patients then drink a large amount of a liquid that contains 50 grams of lactose. Blood samples are taken over a two-hour period to determine the glucose level, which tells how well the body is able to digest lactose. When the lactose reaches the digestive system, the lactase enzyme breaks the lactose down into glucose and galactose. The liver then changes the galactose into glucose. If this process occurs normally, the glucose enters the bloodstream and raises the fasting blood glucose level. If lactose is incompletely absorbed, the blood glucose level does not rise, and a diagnosis of lactose intolerance is confirmed.
The hydrogen breath test measures the amount of hydrogen in the breath. Normally, no hydrogen is detectable in the breath. However, undigested lactose leads to the formation of various gases including hydrogen, by bacteria in the colon. The hydrogen is absorbed from the intestines, carried through the bloodstream to the lungs, and exhaled. In the test, the patient drinks a lactose-loaded beverage, and the breath is analyzed at regular intervals. Hydrogen in the breath means improper digestion of lactose. Certain foods, medications, and smoking can affect the testís accuracy and may need to be avoided before the test.
The lactose tolerance and hydrogen breath tests are not given to infants and young children who are suspected of having lactose intolerance. Giving these patients a lactose load may be dangerous because they are more prone to the dehydration that can result from the diarrhea caused by the lactose. If a baby or young child is experiencing symptoms of lactose intolerance, many pediatricians simply recommend changing from cowís milk to soy formula and waiting for a decrease in symptoms.
If necessary, a stool acidity test, which measures the amount of acid in the stool and presents no risk to young children, may be given. Undigested lactose fermented by colon bacteria creates lactic acid and other short-chain fatty acids that can be detected in a stool sample. In addition, glucose may be present in the sample as a result of unabsorbable lactose in the colon.
What Treatments are Available to Control Symptoms?
Small children born with lactase deficiency should not be fed any foods containing lactose. Most older children and adults need not avoid lactose completely, but individuals differ in the amounts of lactose they can handle. For example, one person may suffer symptoms after drinking a small glass of milk, while another can drink one glass but not two. Others may be able to manage ice cream and aged cheeses, such as cheddar and swiss, but not other dairy products. Dietary control of the problem depends on each personís knowing, through trial and error, how much milk sugar and what forms of it his or her body can handle.
For those who react to very small amounts of lactose or have trouble limiting their intake of foods that contain lactose, lactase additives are available from drug stores without a prescription. One form is a liquid for use with milk. A few drops are added to a quart of milk, and after 24 hours in the refrigerator, the lactose content is reduced by 70 percent. The process works faster if the milk is heated first, and adding a double amount of lactase liquid produces milk that is 90 percent lactose free. A more recent development is a lactase tablet that helps people digest solid foods that contain lactose. One to three tablets are taken just before a meal or snack.
At a somewhat higher cost, shoppers can buy lactose-reduced milk at most supermarkets. The milk contains all of the other nutrients found in regular milk and remains fresh for about the same length of time.
A Nutrition Balancing Act
Milk and other dairy products are a major source of nutrients in the basic American diet. The most important of these nutrients is calcium. Calcium is needed for the growth and repair of bones throughout life, and in the middle and later years, a shortage of calcium may lead to thin, fragile bones that break easily (a condition called "osteoporosis"). A concern, then, for both children and adults with lactose intolerance is how to get enough calcium in a diet that includes little or no milk.
Although the RDA (recommended daily allowance) for calcium, set in 1980, is 800 mg per day, many experts in bone disease believe this is too low. The results of a 1984 conference at the National Institutes of Health (NIH), suggest that women who have not yet reached menopause and older women who are taking the hormone estrogen after menopause should consume about 1,000 mg of calcium daily (roughly the amount in a quart of milk). Pregnant women and nursing mothers need about 1,200 mg of calcium per day. Postmenopausal women not taking estrogen may need as much as 1,500 mg of calcium per day. The RDA for adult men is 1,000 mg per day and 1,500 mg per day for men in their later years.
It is important, therefore, in meal planning to make sure that each dayís diet includes enough calcium, even if the diet does not contain dairy products. Quite a few foods are high in calcium and low in lactose. Many green vegetables and fish with soft, edible bones are excellent examples. To help in planning a high-calcium/low-lactose diet, the following chart lists some common foods that are good sources of dietary calcium and shows how much lactose the foods contain.
Recent research has shown that yogurt may be a very good source of calcium for many lactose intolerant people, even though it is fairly high in lactose. There is evidence that the bacterial cultures used in making yogurt produce the lactase required for proper digestion.
Clearly, many foods can provide the calcium and other nutrients the body needs, even when intake of milk and dairy products is limited. Still, factors other than calcium and lactose content should be kept in mind when planning a diet. Some vegetables that are high in calcium (Swiss chard, spinach, and rhubarb, for instance) are not listed in this chart because the body cannot use their calcium content. They contain substances called oxalates, which stop the calcium absorption. Remember also that calcium is absorbed and used only when there is enough vitamin D in the body. A balanced diet should provide an adequate supply of vitamin D.
Some people with lactose intolerance may think they are not getting enough calcium and vitamin D in their diet. A doctor is the best person to decide whether any dietary supplements are needed. Taking vitamins or minerals of the wrong kind or in the wrong amounts can be harmful. A dietitian can help in planning meals that will provide the most nutrients with the least chance of causing discomfort.
Some so-called nondairy products such as powdered coffee creamer and whipped topping also may include ingredients that are derived from milk and therefore contain lactose.
Smart shoppers learn to read food labels with care, looking not only for milk and lactose among the contents but also for words such as whey, curds, milk by-products, dry milk solids, and non-fat dry milk powder. If any of these are listed on a label, the item contains lactose.
In addition, lactose is used as the base for more than 20 percent of prescription drugs and about six percent of over-the-counter medicines. Many types of birth control pills, for example, contain lactose, as do some tablets for stomach acid and gas. A pharmacist can answer questions about the amounts of lactose in various medicines.
Watch for Hidden Lactose
Although milk and foods made from milk are the only noteworthy natural sources, lactose is often added to prepared foods. It is important for people with very low tolerance for lactose to know about the many foods that contain lactose, even in small amounts. Grocery items that may contain lactose include: