Types:

There are different types of lactose intolerance, in addition to which there are other causes of intolerance to lactose.

Different reviews and reports group Lactose Intolerance (LI) differently. Some categorise them in two groups while others in three. However, they always refer to the conditions correctly. It is a matter of opinion whether one of the conditions that causes LI fits in one group or is presented in a separate group. I prefer to subdivide LI or Lactase deficiency in three groups as in my opinion this is a more logical way.

Hence, there are three groups of Lactase Deficiency:

• Congenital Lactase Deficiency: two types of very rare genetic disorders
• Primary Lactase Deficiency: most common, around 75% of the world population
• Secondary Lactase Deficiency: caused by a disease or condition and may be only temporary

Congenital Lactase Deficiency

There are two types of Congenital Lactase Deficiency (CLD) and they have identical symptoms. CLD, inherited as an autosomal recessive trait, are rare genetic conditions. In this type there is a marked deficiency of lactase production if any at all in the small intestine from birth. It is caused when a baby inherits two ineffective genes from the parents (one from each). This results in an inability of the genes in the newborn to produce enough lactase or nothing at all. There is abnormal absorption of lactose and other disaccharides from the gastric mucosa. CLD is characterised by severe diarrhoea, abdominal pain, vomiting dehydration, renal tubular acidosis, aminoaciduria, liver damage, lactosuria, cataracts and distension that appear soon after birth when the diet begins to contain lactose. The baby will fail to thrive, but a milk free diet leads to rapid recovery, and after 6 months of age a normal diet with some milk may be tolerated.

Blood sugar rises normally after oral administration of glucose or galactose, but not after lactose, which may induce explosive diarrhoea, flatulence and intestinal discomfort. Bacterial fermentation of ingested lactose in the colon leads to high concentrations of lactic acid which make the stool very acidic.

The second type, also called Familial Lactase Deficiency is the result of a defective lactase enzyme protein. Unlike CLD the level of lactase enzyme production is normal but since the genes are producing a defective enzyme, lactase is deemed dysfunctional and ineffective.

Treatment for both types is initially with a lactose free diet and food treated with commercially available lactase enzymes.

Primary Lactase Deficiency

PLD is usually referred to those persons who do not produce enough lactase after weaning. This type is also called Late Onset Lactase Deficiency. This by far the most popular and accounts for more than half the world population. However, another type of PLD, not talked about very much is present in premature babies whose underdeveloped small intestines are not mature to produce enough lactase.

Late Onset Lactase Deficiency

Also know as Adult Lactase Deficiency. This is by far the commonest of them all. Late Onset Lactase Deficiency is also considered as the commonest genetical disorder of all disorders (but is it really a disorder?). Enzyme levels are highest shortly after birth and decline with aging, despite a continued intake of lactose. Within the animal world, nonhuman mammals usually lose the ability to digest lactose as they reach adulthood. Some populations of the human species, including those of Asian, South American, and African descent, have a propensity for developing lactase deficiency. By contrast, races descended from northern Europe or from the north-western Indian subcontinent are likely to retain the ability to absorb lactose into adulthood. Late onset lactose intolerance occurs several years after birth and is unlikely to be a problem until after 5 to 7 years of age.

Lactose, a disaccharide (two single sugars attached to each other), is present in milk and processed foods. Dietary lactose must be hydrolyzed to a monosaccharide (single sugars) in order to be absorbed by the small intestinal mucosa. A deficiency of intestinal lactase prevents hydrolysis of ingested lactose. The osmotic load of the unabsorbed lactose causes secretion of fluid and electrolytes until osmotic equilibrium is reached. Dilation of the intestine caused by the osmosis induces an acceleration of small intestinal transit, which increases the degree of maldigestion. Within the large intestine, free lactose is fermented by colonic bacteria to yield short-chain fatty acids and hydrogen gas. The combined increase in faecal water, intestinal transit, and generated hydrogen gas accounts for the wide range of gastrointestinal symptoms.

Symptoms of lactose intolerance include loose stools, abdominal bloating and pain, flatulence, nausea, and borborygmi. A diagnosis or even the suggestion of lactose intolerance leads many people to avoid milk and/or consume specially prepared food with digestive aids, adding to health care costs.

It is common for premature babies to be lactase deficient. As they develop most of them will be able to start producing enough lactase.

Development Lactase Deficiency

DLD is the other type of Primary Lactase Deficiency. It results from low lactase levels and is a consequence of prematurely born babies. Lactase activity start during late gestation periods. Hence, a prematurely born baby will acquire lactose intolerance due to lack of enzyme production.

The list below shows the activity of lactase in the foetus as it increases with gestation:

• 23rd week 10% of full term
• between 25th and 34th is 30% of full term
• between 34th and 35th week 70% of full term

Premature infants born at 28 to 32 weeks of gestation have reduced lactase activity that will lead to severe cramps, abdominal pains, diarrhoea, continuous discomfort and crying. These symptoms may be very similar to babies suffering form baby colic.

Lactose free milk, or milk treated with lactase enzyme should alleviate the symptoms.

Secondary Type Lactase Deficiency

Secondary lactase deficiency can result from small intestinal resections, and from gastrectomy and from diseases that damage the intestinal epithelium, e.g. untreated coeliac disease or intestinal inflammation. Another source of secondary type lactase deficiency is a long course of antibiotics. When the epithelium heals, the activity of lactase returns. However, according to American Journal of Clinical Nutrition, Vol 60, 926-929,  Arrigoni et al. secondary maldigestion does not automatically lead to severe symptoms of intolerance.

The following is a list of intestinal diseases that may cause a secondary type lactase deficiency:

• Giardiasis:
• Ascariasis:
• Crohn disease:
• Coeliac sprue:
• Tropical sprue:
• Radiation sprue:
• Diabetic gastropathy:
• Carcinoid syndrome:
• Qhipple syndrome:
• HIV enteropathy:
• Kwashiorkor:
• Chemotherapy:
• Gastrinoma:

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