RESEARCH PROJECT TOPIC ON
Lactose Intolerance In Port Harcourt
Plasma glucose concentration was determined by lactose tolerance test (LTT) in twenty-nine subjects, among who are twenty one females and eight males, before and after ingestion of 170g of liquid milk. Although none of the subjects was milk tolerant but there were remarkable rises and falls in plasma glucose levels at certain time intervals in some of the categories of subjects. The highest rise among two regular milk consumers was 2.2 and 2.3 mmo1/l respectively. And a fall of 2.6mmol/1 registered by a subject among non-milk consumers. The overall conclusion from the results of this survey points to the fact that lactase enzyme may be adaptive in nature.
TABLE OF CONTENTS
Title Page – – – – – – – – – – i
Declaration – – – – – – – – – ii
Dedication – – – – – – – – – iii
Acknowledgement – – – – – – – – iv
Abstract – – – – – – – – – – v
Table of Contents – – – – – – – – vi
Introduction and Literature Review
Materials and Methods
Discussion and Summary
LIST OF FIGURES AND TABLES
Table 1: Plasma Glucose Concentrations (mmo1/1) in all the subjects before and after intake of 170g of milk
Table 2: Plasma Glucose Concentrations (mmo1/1), before and after intake in subjects who take milk regularly.
Table 3: Plasma Glucose Concentrations (mmo1/1), before and after intake in subjects who take milk occasionally.
Table 4: Plasma Glucose Concentrations (mmo1/1), before and after intake in subjects who have symptoms after milk intake.
Table 5: Plasma Glucose Concentrations (mmo1/1), before and after intake in subjects who have not had milk for several years.
Figure 1: Mean Plasma Glucose Concentration (PGC) in 4 different groups of subjects after ingestion of milk (170g each).
Figure 2: Mean Plasma Glucose Concentration (PGC) in 4 different groups of subjects after ingestion of milk (170g each).
Lactose accounts for a tenth of total dietary carbohydrate and is a disaccharide containing glucose and galactose. It is found only in milk, hence it is sometimes called milk sugar, and makes up to half the total solids in milk. Lactose was first identified in 1633 (Guthrie, 1971). It is a reducing disaccharide with a (1 4) – B-D-galactosidic linkage to D-glucose.
The structure of D-glucose and D-galactose pyranose rings differ only in the configuration around C4; a point which is important in the metabolism of D-galactose and therefore of lactose (Montgomery et al, 1974).
Specific mal-digestion of disaccharides (maltose, isomaltose, sucrose and lactose) results from deficiency of a specific enzyme that digests the earlier mentioned disaccharides. Isolated enzyme deficiencies are mainly congenital and with the exception of lactose enzyme deficiency are rare (Muir, 1980).
The deficiency or diminished activity of the enzyme lactose results in lactose or milk intolerance. Lactase is found in the cell membrane of epithelial cells of the brush border in the small intestines. Here it catalyzes the hydrolysis of lactose in milk to glucose and galactose, which are absorbed and transported via the blood in the portal system to the liver. Here galactose is converted to glucose. Some of the latter is stored as glycogen in the liver while the rest is transported by the blood to various body tissues.
Failure to hydrolyze lactose due to lack or reduced activity of lactase in the small intestines results in un-hydrolyzed lactose in the small intestinal lumen. The osmotic effect of un-hydrolyzed lactose and the irritation of the bowel by lactic acid produced due to bacterial action on lactose result in diarrhea as well as bloating and flatulence (Anderson, 1963). These are the clinical symptoms of mal-digestion of lactose when the gut is challenged by milk or lactose meal.
It is reported that most infants have a high level of the enzyme lactase, but this declines after 2 to 4 years of age (Muir, 1980). Yet a few infants have congenital deficiency, just as occurs in older children and adults whose condition has persisted since infancy. This congenital or primary lactase deficiency is believed to be permanent and resulting from a genetically determined enzyme defect or from the environment or both (Cook, 1966; Keusch, 1969). It has been suggested that lactose deficiency is an autosomal recessive supported by Rosenweig et al in 1967, who believe that lactose intolerance is an inherited disorder because of the striking racial differences in the incidence. They have noticed a 100% occurrence of a positive family history of milk intolerance in 9 healthy children. In another survey of 40 healthy adults, they reported that lactase activity tended to fall into three groups:
i. A high activity group, with over 7 units per gram of mucosa in which 8 people are milk and lactose tolerant.
ii. A low activity group, with less than 2 units, in which all 15 people are both lactose and milk intolerant.
iii. An intermediate activity group, ranging from 2 to 7 units, in which there are 17 people. Six of whom have milk and lactose induced symptoms. They suggest that those in the high and low groups might be homozygous while the intermediate group might be heterozygous for lactase deficiency.
The prevalence of congenital lactase deficiency remains disputed, but Sodeman and Sodeman (1974) noticed that lactose intolerance most frequently affects Negroes, Orientals and Cypriot Greeks than Caucasians. This was supported by a report that about 90% of Caucasians of Northern European extraction and 80% of members of two African tribes, continue to secrete lactase and therefore can tolerate lactose and milk, but 70% to 80% of older children and adult of other races and ethnic groups secrete little or no lactase and are therefore lactose and milk intolerant (Muir, 1980).
The incidence of lactase deficiency that leads to lactose intolerance can be as low as 16% (Auriccho et al, 1963) and as high as 89% (Newcomer and McGill, 1966). They also suggest that racial differences may account for part of the variations. Lactase deficiency is noted in 30 of 41 Baltimore blacks (Cauatrecasas et al, 1965) and flat lactose tolerance tests in 31 of 35 Bantus in Uganda (Cook, Kajubi, 1966).
Apart from congenital etiology of lactose intolerance which is considered rare (Cautrecases et al, 1965), lactose mal-digestion and mal-absorption can be acquired in children and adults as a result of many factors, these include:
i. Mucosal abnormalities such as sprue and occasionally regional enteritis (Kern, Jr. and Struthers, Jr. 1966).
ii. Gastrojejunostomy (Gryboski et al, 1963).
iii. Transient infections enteropathies (Kleijers and Van de Kamer, 1962).
iv. Giardiasis (Durand and Lamedica, 1962)
v. Cystic fibrosis (Cozzetto, 1963).
vi. Adult celiac disease and other mal-absorption states with blunting of microvilli (Cooke et al, 1963), Pletkin and Isselbacher, (1964).
Apart from disease states, other investigators suggest that lactose intolerant syndrome may result from:
i. Normal spectrum of development in adult mammal; and
ii. Secondary to lack of stimulation by the substrate lactose (Kern, Jr. and Struthers, Jr. 1966).
Mal-nutrition also plays a role in lactose intolerance especially in cases of advanced Kwashiorkor (Dean, 1957) and mal-nourished children (Cevini et al, 1962; Careddu et al, 1963; Bardare et al, 1965; Kerpel-Fronius et al, 1966).
Drug induced lactose intolerance is significant with several antibiotics. Keating et al. (1974) associated it with ampicillin therapy. This was also supported by Tedesco (1975), Beavis, Parsons and Salfield (1976).
Isolated deficiencies of the various disaccharides have been described but lactase deficiency is the most frequent and best understood (Sodeman and Sodeman, 1974). Temporary lactase mal-absorption has been shown to occur in children during bacterial or non-specific diarrheal diseases (Sunshine and Kretchner, 1964; Cevini et al, 1962), and during massive Giardia lamblia infestation (Durand et al, 1963; Mardio et al, 1963). It is difficult to understand why lactase enzyme should be singled out for damage but sparing the other three alpha glycosidases – namely sucrose, maltase and isomaltase. It is even more difficult to imagine that the defect can be permanent after the under-lying condition is relieved. But lactase normally has a much lower activity than the three – glycosidases and a decrease in all enzymes following a non-specific injury will become manifest primarily by an impaired lactose tolerance. Again, lactase may be the only enzyme most susceptible to permanent damage (Haemmerli et al, 1965).
Most recent studies with rats, rabbits, calves and humans shows that lactase appears late during gestation, reaches a maximum shortly after birth and falls gradually to a plateau (Heilskov, 1952; Alvarez 1961; Doell and Kretchmer, 1962). Attempts to prevent the fall after birth, or to increase the adult level by administering oral or intraperitoneal lactose, have failed (Heilskov, 1952; Alvarez and Sas, 1961; Doell and Kretchmer, 1962; Forster et al, 1963). Fischer (1957) however, found that the diarrhea of rats on 25% lactose diet ceased after prolonged ingestion, and that the total intestinal lactase increased, but this was balanced by a 50% increase in mucosal weight.
Diarrhea can invariably be produced by dietary lactose, although the threshold differs with species and age (Cuatrecases et al, 1965). However absorption can be improved and diarrhea disappear with prolonged intake in animals (Whitter et al, 1935; Riggs and Beauty, 1947, Lawrence, 1950; Fischer and Sutton, 1953) and in human infants (Lamedica et al, 1962). Cuatrecasas et al (1965) have shown the same effect with human adults. Therefore, adaption to lactose evidently occurs but it has an enzymatic basis. Girardet et al (1963) suggested that lactase activity in the gut varies with dietary lactose in adult rats.
Cuatrecasas et al (1965) demonstrated that lactase is not lost with advancing age. They support the thesis that lactase deficiency in the adult results from prolonged milk and lactose that is substrate deprivation. Attempts to improve absorption ratio or raise lactase activity with short-term dietary measures have so far failed. So Cuatrecasas et al suggested long-term dietary measure, consisting of increase intake of milk or lactose for improved tolerance.
Lactase deficiency or lack which culminates in lactose or milk intolerance may be a latent condition, but manifest when the gut is challenged with a diet high in milk or lactose. A previously asymptomatic lactase deficiency may become evident also when combined with other gastrointestinal diseases mentioned earlier because of:
i. An increased lactose load contained in an ulcer diet.
ii. Increased rate of gastric emptying following gastric resecting, or
iii. Concurrent development of functional or inflammatory intestinal disease (Sodeman and Sodeman, 1974).
Proposed criteria for diagnosis of lactase deficiency include:
i. Diarrhea, borborygmi, cramping abdominal pain and flatulence after milk or lactose ingestion;
ii. Absence or diminished lactase activity in mucosal biopsy specimen.
iii. A flat lactose tolerance curve – obtained by serial determination of plasma glucose level at 30 minutes interval for two hours after milk or lactose intake.
In children, the dosage of lactase is 2g/kg of body weight (Basferd, 1967; Gudmand-Hoyer, 1977). Adult dose is 50mg lactose – equivalent to 1 liter of milk or 100mg of lactose. A control test may be performed using 25g glucose and 25g galactose, if the test indicated mal-absorption.
Patients with lactase deficiency exhibit a peak rise less than 20mg/d1 (1.1mmo1) of plasma glucose level. A group in Chicago noticed that a physiological dose of 50mg of lactose did not produce symptoms earlier mentioned, but showed severe symptoms with 100mg lactose in subjects considered lactase deficient. These subjects are said to be “clinically norm” but considered “forme fruste” of the full syndrome (Haemmuli et al, 1965). Peternel (1965) reported that symptoms in patients with lactase deficit appeared to depend on the ingestion of threshold quantities of lactose or milk. And that it is common for milk intolerance to be identified for the first time when the threshold quantities are exceeded. So manifestations of lactose intolerance appeared to be dose related. In their interpretation of reports from a Zurich group of investigators – (Auricchio et al, 1963; Haemmali et al’ 1963; 1964 and 1965) – James et al (1965) suggested that normal lactase levels are almost always associated with a maximal rise of at least 20mg (1.1mmol) while deficit levels are usually associated with sub-stantially smaller increments. For this reason, they disagree with Haemerli et al. who stated that “a flat glucose curve alone after an oral lactose load is meaningless.” They are also in disagreement with the implication of Kochler et al, (1935); Girardet et al, (1963) and Isselbacher et al. (1964) that “flat” lactose tolerance curves may occur in 25% or more of “normal” adults. They experience that lactase-deficient state appears to be common enough to account for high incidence of “flat” curves support their disagreement with the other investigators.
Investigators infer that 55% of adults are intolerance to lactose due to the deficiency of jejunal B-galactosidase and cellobiase, with consequent inability to hydrolyse dietary lactose.
Evidence is strong that lactase deficiency may be an acquired trait and also that it may be an adaptive enzyme, because this deficiency correlates with dietary milk or lactose deprivation, for there is loss of symptoms with prolonged milk or lactose intake, but decreased absorption with milk restriction. For instance, large quantities of milk are consumed in the northern parts of Nigeria with no apparent ill-effects, for milk is part of their cultural dietary intake; especially amongst the nomadic communities, whereas the consumption of relatively smaller quantities of milk in the southern communities of Nigeria causes symptoms of milk intolerance such as mentioned earlier.
As far as is known, there is no published work in the incidence of lactose or milk intolerance in the southern part of Nigeria. The purpose of this work is therefore to investigate the extent and the pattern of milk (lactose) intolerance in a community in southern Nigeria.