W. Steven Pray, PhD, DPh; Joshua J. Pray, PharmD Candidate

Disclosures

July 01, 2004

During most of the 1960s and 1970s, there was little awareness of lactose intolerance among Americans. The majority of Americans were of Northern European descent, a group that rarely is lactose intolerant. However, multiple factors have led lactose intolerance to slowly assume more prominence in the minds of American pharmacists as one of the most common physical conditions affecting humankind.

During the 1960s and 1970s, dynamic changes in American demography eventually brought an increasing number of lactose-intolerance patients to the pharmacist for counseling. Asian and Hispanic minorities, two groups with high degrees of lactose intolerance, rapidly increased in numbers. Further, mainstream companies successfully marketed products to ethnic minorities, giving more emphasis to specialty markets, such as those predominantly aimed at African-Americans, who also have a high prevalence of lactose intolerance.

Milk is a polynutrient that has many healthy components. Its major carbohydrate is lactose, a disaccharide.[1] Humans cannot absorb lactose for use as a calorie source unless they can first break it down into its monosaccharide component sugars: glucose and galactose. This is achieved through the intervention of lactase, an enzyme belonging to a group known variously as disaccharidases or beta-galactosidases. Inner lumen small intestinal cells known as enterocytes are covered with a membrane that has a brush border. The brush border microvilli produce lactase. (Unfortunately, lactase is produced in the upper, most shallow section of the villi, an area exceedingly prone to damage by secondary insults such as medications or diseases.)

In humans there is a condition known as congenital alactasia, but it is extremely rare; only a few cases have ever been reported. Other mammalian babies, like most humans, produce sufficient lactase to digest maternal milk. The ability to digest milk endures until the baby is weaned. After weaning, other mammals naturally graduate to life as a vegetarian, carnivore, or omnivore. Thus, there is no question of lactose intolerance in the animal world. Most adult animals refuse to drink milk. Although many people give domesticated adult cats milk in the mistaken belief that it is needed, cats that drink milk often have diarrhea due to lactose intolerance. In man, lactase activity drops at about age 2 or 3 and may be absent by age 5 to 10.[1]

Some humans retain the ability to digest milk as adults. The reason for this is unknown, but an intriguing theory involves the role of evolutionary adaptation to environmental stressors. Throughout prehistory, man struggled mightily to obtain the basic resources needed for survival, including shelter, clothing, and food. In regard to food, famine swept through entire countries, devastating the population. Crops failed and game became scarce. In many cultures, famine meant death for most residents. However, experts note, Northern Europeans began to move from a hunter-gatherer lifestyle to an agrarian lifestyle thousands of years ago. One of the innovations was the domestication of ruminants such as cows and goats. If a village were in the throes of widespread famine, the theory suggests that some robbed the domesticated cows of milk, feeding it to the children and adults to stave off starvation. While the infants, who still produced lactase, would survive, most older children and adults would have been unable to use the milk. However, the theory suggests that scattered residents had not undergone the normal postweaning loss of lactase. Rather, due to a genetic mutation, they had been producing lactase on an uninterrupted basis since birth. This phenomenon has since become known as lactase persistence. Lactose-intolerant villagers died, but those with the mutation lived on cow's milk and survived to have children, who received their gene for lactase persistence. Natural selection would have continued with subsequent famines. Eventually, historians conceive of a culture with repeated famines in which lactose intolerance would have been a lethal nonadaptation to prevalent and recurring environmental disasters. Although this is only theoretical, certain demographic data fit well. For instance, domesticated ruminants were characteristic of Northern Europe but not of Africa, Asia, or the Arctic. The primary domesticated animal in Asia is the pig, an animal that does not lend itself to milking. Further, some Bedouin tribesmen are lactase persistent. Perhaps in dry desert areas, water was often unavailable, causing Bedouins to drink milk from the camel, which has an udder like a cow. Thus, they may have eventually developed the same phenotype as their Northern European counterparts.

If a physician wishes to confirm lactose intolerance, a small intestinal biopsy can be ordered to assay for lactase.[1] An alternative test involves administration of 50 grams of lactose, followed by serial withdrawal of blood samples.[1] Lactase persistence is indicated if the blood glucose rises significantly in 15 to 45 minutes. (The 50-gram amount was chosen because it is the amount present in 1 liter of whole milk.[2]) Physicians may also give a lactose load along with ethanol, which prevents hepatic conversion of the galactose to glucose, checking the urine for galactose.

Another method of diagnosing lactose intolerance relies on the fact that those who lack lactase pass undigested lactose into the large intestine, where it undergoes bacterial fermentation, the cause of excessive gas. Among the byproducts of fermentation are fatty acids and gases. Hydrogen, one of the gases, is excreted in the patient's breath.[2,3] Hydrogen in the breath is measured following ingestion of a standard glucose load.

This month's patient leaflet recognizes that most patients do not need to undergo sophisticated tests to determine whether they are lactose intolerant. It describes a method whereby the patient can become an observer of their responses to ingestion of foods to gauge the extent of their ability to digest lactose. This method is particularly useful because some of the traditional tests are less than optimal. For instance, the 50-gram lactose loading is unrealistic. Few patients consume 1 liter of milk in a meal. Most patients consume about 8 ounces of milk, which contains 12 grams of lactose. Thus, discovering their tolerance on their own through experimentation actually educates patients about what is realistic for them to do to avoid troubling symptoms.

The pharmacist can provide assistance to patients with lactose intolerance. In addition to instructing them on the differences between milk allergy and lactose intolerance and the risks of osteoporosis, pharmacists can also point out the benefits of using lactose-free milk, milk substitutes, and tablets and liquids that contain lactase.[4,5,6,7]

Lactose-Free Milk: Lactose-intolerant patients can choose from several lactose-free milks. The Lactaid brand is available as three lactose-free choices: reduced-fat Lactaid, low-fat Lactaid, and nonfat Lactaid milks (45, 20, and 0 fat calories per cup, respectively). Another group is lactose-free Dairy Ease whole milk, reduced-fat 2% milk, and nonfat milk.

Milk Substitutes: Several milk substitutes offer a taste that may be acceptable. Patients should be urged to try another variety if one is not quite to their taste. Milk substitutes include soybean oil mixtures (eg, 8th Continent Soymilk), rice-based products, and mixtures of several ingredients (eg, Vitamite, containing corn syrup solids, canola oil, potassium caseinate, soy protein). Some of the products are enriched with calcium; these are preferable.

Lactase Tablets/Liquids: Patients may try lactose-free milk or milk substitutes and find them unacceptable. Further, most restaurants do not offer lactose-free foods or dairy substitutes. In these cases, ingesting lactose along with exogenous lactase tablets may prevent problems. To assess the usefulness of lactase-containing tablets, the patient can perform a test. The evening before the test, the patient should not eat anything after 10 pm. Along with a normal breakfast, the patient should drink 12 ounces of milk, keeping track of symptoms over the next six hours. On the second day, the patient should repeat the regimen, adding a lactase supplement (eg, Lactaid Ultra) with the first swallow of milk. If symptoms occur, the patient may simply increase the dose of lactase product as directed on the label until he or she is symptom-free. Since ingestion of lactase is free of adverse effects, the patient may continue to increase the dose until symptom-free. From that point, the patient should take care to ingest the same number of tablets for every 12 ounces of milk or its equivalent.

Some products (eg, Lactaid) are also available as drops. The patient may take them orally as an alternative to tablets or may use them to prepare their own lactose-free milk from regular milk. To do this, the patient purchases a cow's milk product, adds the suggested number of lactase drops, and shakes the carton. After approximately 24 hours, digestion of lactose is complete. Patients who choose this option may notice that the milk is sweeter than standard milk. They should be reassured that the enhanced sweetness results from the fact that glucose and galactose are sweeter than lactose, the parent compound. Eventually, they will become accustomed to the difference.

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