Lactose Intolerance

Page 1 2 3

What is Lactose Intolerance?

Virtual Medical Centre Video

Lactose intolerance, or intolerance to lactose-containing foods (such as dairy products), affects primarily the gastrointestinal tract, though it can have effects on other systems as a result of nutritional deficits that result from the condition.

Lactose intolerance can be either primary, or secondary to damage to the gastrointestinal tract.

Who gets Lactose Intolerance?

The prevalence of primary lactose intolerance is estimated to be 7 to 20% for people of Caucasian descent, 65 to 75% for African descent, over 90% in some Asian populations and approximately 70% in Australian Aboriginal populations.

The prevalence of secondary lactose intolerance is difficult to measure.

Predisposing Factors

The symptoms of lactose intolerance occur when people with a deficiency of lactase ingest foods containing lactose. Lactose intolerance can be divided as primary or secondary, depending on the cause of lactase deficiency.

Primary lactase deficiency can be caused by:

Racial or ethnic lactase deficiency, which is the most common (see below).
Developmental lactase deficiency, which occurs in premature infants born at 28 to 32 weeks gestation.
Congenital lactase deficiency, which is a rare autosomal recessive condition where infants have diarrhoea from birth, and used to be fatal before the introduction of lactose-free formulas. It is most common in the Finnish population.

Racial or ethnic lactase deficiency is a genetically determined reduction of lactase activity and the most common cause of lactose intolerance. In most of the world's population, a drop in lactase levels occurs at 5 years of age, most prominently in Asian and African populations, and also in Australian Aboriginal populations. In contrast, the majority of the Caucasian population, and in particular in people of Scandinavian background, higher levels of lactase activity persist into adulthood.

In practice, lactase activity is normal in virtually all healthy children of any racial or ethnic group until approximately 5 years of age, and hence lactose intolerance detected in younger children usually indicates an alternative primary cause of lactase deficiency or a secondary cause of lactose intolerance.

Secondary causes of lactose intolerance include:

Bacterial overgrowth, which is associated with increased fermentation of lactose in the small bowel.
Gastrointestinal infections.
Injury to the lining of the gastrointestinal tract, including coeliac disease, inflammatory bowel disease (in particular Crohn's disease) and drug or radiation induced enteritis.

Progression

The natural history of lactose intolerance varies according to the cause. In the most common form of lactose intolerance, lactase activity falls from around 5 years of age, and symptoms begin to occur after consumption of more than approximately 250ml of milk. The symptoms will vary between people in their severity and the discomfort that they cause. Low levels of lactase are permanent in most populations after this age.

In some secondary causes of lactose intolerance, lactase levels fall transiently. For example, many people find that they become relatively lactose intolerant after gastroenteritis, or a viral tummy infection. This is due to damage to the cells that produce lactase, and once these cells recover and begin to produce lactase again, symptoms of lactose intolerance disappear.

Lactose intolerance is not lethal, and morbidity is low. Sometimes people who are lactose intolerant avoid dairy products to an extent in which their intake of calcium is greatly reduced, and if they do not take calcium supplements or otherwise increase their daily intake of calcium, they may develop osteopenia, or thin bones. Most people with lactose intolerance can tolerate enough milk or other dairy products to get their required daily intake of calcium, but if this is not the case, calcium supplementation is recommended to avoid development of osteopenia, which can lead to osteoporosis (brittle bones).

Page 1 2 3