Chapter 6b
LACTASE DEFICIENCY
1. OVERVIEW
Lactase deficiency is widespread throughout the world and is not really a disease: it is normal for young mammals designed to derive energy from maternal milk containing lactose to progressively lose their lactase after weaning. Adult mammals do not normally have access to milk so the possession of small intestinal lactase is redundant. In humans lactase activity falls at about age five. In nature, lactose only occurs in milk; in virtually all placental mammals except sea lions, lactose is the carbohydrate in milk: in macropods such as kangaroos milk does not contain lactose so that baby kangaroos (Joeys) reared on cow’s milk develop cataracts from galactosaemia from their inability to metabolise galactose. However in Northern Europeans and in those living in the north-west of the Indian Subcontinent, lactase tends to persist in the adult, probably because there is a survival advantage in being able to utilise milk products such as cheese, through the winter when food supplies may be limited. Interestingly, the Dutch, renowned for their dairy products such as cheese, have the lowest prevalence of lactase deficiency of any group studied. We may conclude that lactase deficiency (so called alactasia or lactose intolerance) is not a disease but that the persistence into adulthood of lactase is a biological adaptation to the use of milk products in certain societies. The ICD 10AM Code is E73.
Lactase is an enzyme found in the brush border of the small intestine. It breaks down lactose into the six carbon sugars glucose and galactose. From the duodeno-jejunal junction its concentration rises rapidly to a plateau at about 50cms from the duodenal-jejunal junction and declines rapidly from
about 150cms to 0 at the ileocaecal junction but the histology of the small intestine is quite normal.
The frequency of lactase deficiency varies throughout the world.
Table 2 . Prevalence of lactose intolerance (1)
Group Prevalence %
Orientals in the US 100
Black Americans 81
Italians 71
Australian aborigines 67
White Americans 24
Dutch 0
There is a major discordance between the intestinal levels of lactase and the symptomatology. The typical picture is of discomfort soon after milk or milk products. This may take the form of colicky abdominal pain, nausea, a sense of abdominal distension with flatus and possibly brief, brisk, watery diarrhoea. Many people have no symptoms at all with the level of symptoms being modified by factors such as dose of lactose, accompanying food and fibre, the rate of intestinal transit and the colonic flora. Lactose escaping to the colon may be rapidly metabolised by the resident flora without production of symptoms. The range of tolerance to lactose in those deficient in it is illustrated by the fact that one study showed that 50g of lactose will produce symptoms in 70-80% of lactose malabsorbers whereas 10g, such as contained in 200 mls in a glass of milk will only produce symptoms in 30- 60% of subjects. (2)
2. DIAGNOSIS
This may be suggested by a dietary history and the effect of milk upon symptoms, the symptomatology overall and the ethnic background of the patient. Various diagnostic approaches have been suggested. A brisk response to a milkshake is virtually diagnostic but lacks sensitivy. At the other end of the scale is small bowel biopsy with analysis of the enzyme level in a biopsy specimen. Lactose tolerance tests are less invasive. One
68 Chapter 8 6b
LACTASE DEFICIENCY 69 involves the measurement of blood glucose levels or breath hydrogen levels after a lactose load.
3. SECONDARY LACTASE INTOLERANCE
This occurs in a number of situations. A standard one is post gastrectomy due to the rapid dumping of gastric contents into the intestine.
It also occurs in small bowel mucosal diseases such as coeliac disease, tropical sprue, or short bowel syndrome. It has been also reported in other mucosal disorders even duodenal ulcer.
4. MANAGEMENT
The vast majority of patients will respond to a low lactose diet with the restriction of obvious milk products, it is said that rarely patients are even sensitive to the minute amount of lactose in some tablet formulations. The form of the food is important. It has been claimed that equivalent amounts of lactose given as yogurt are much better tolerated than lactose alone (3).
Particularly in children, it is essential to provide an alternative source of calcium. Scrutinizing of food labels is also important. Commercially,
“lactase” preparations, really bacterial or yeast ȕ galactosidases are available and of variable value. Live culture yoghurt, which contains endogenous ȕ galactosidase is an alternative containing both calcium and calories.
Essentially the management of lactose intolerance consists of tailoring the lactose component of the diet to the patient’s tolerance; little is gained by the use of a lactose free diet if the patient can tolerate some lactose.
5. PROGNOSIS
Lactose intolerance has no complications and once established apparently by the primary form is permanent.
6. SECONDARY FORMS
The prognosis of secondary forms depends upon adequate restoration of normal small intestinal anatomy. There is a very rare congenital form of alactasia, a condition with severe consequences for a neonate.
References
1. Buller HA, Grand RJ. Lactose intolerance. Annu. Rev. Med. 41,141-8 (1990).
2. Gudmand-Hoyer E, Simony V. Individual sensitivity to lactose malabsorption. Am. J.
Dig. Dis. 22,177-81 (1977).
3. Kolars J, Levitt MD, Anouiji M, Savaiano DA. Yogurt - auto digestive source of lactose.
N. Engl. J. Med. 310,1-3 (1984).
700 Chapter6b
