What is lactose
intolerance?
This is a condition
caused by inability to digest one of the carbohydrate components of milk,
specifically lactose, due to a lack of the intestinal enzyme lactase, which is
essential for the efficient metabolism of lactose (milk sugar).
This condition can
first show itself in the neonatal period with vomiting and profuse diarrhoea
after milk ingestion, which resolves when lactose-free fluids are fed to the
infant. However, it can also show up only in adulthood.
It is
not known why some people are deficient in the enzyme lactase.
Because of the lack of
lactase, the lactose in milk is not broken down. It remains in the gut, where
it causes fluid retention which results in diarrhoea. This, together with
bacterial fermentation of the milk sugar in the colon leads to abdominal
cramps, distension, and gaseous, acidic stools.
A transient lactase
deficiency may develop after an infant has undergone a protracted period of
diarrhoea or has had a large segment of small bowel removed.
Lactase
deficiency occurs normally in about 75% of adults in all ethnic groups except
those of northwest European origin for whom the incidence is less than 20%.
Although statistics are
unreliable, most nonwhites gradually lose the ability to digest lactose between
the ages of 10 to 20 years. It affects 90% of Orientals, 75% of blacks and
Indians, with a high incidence among people from the Mediterranean region
A child
who cannot tolerate lactose will have diarrhoea and fail to thrive.
An adult may have
bloating, flatus, nausea, diarrhoea and abdominal cramps. When lactose
absorption is impaired by deficiency of the enzyme lactase, the resulting
diarrhoea may be severe enough to purge other nutrients before they can be
absorbed.
A history of milk
intolerance may be obtained in patients with lactose intolerance. Some people
recognise this early in life and consciously or unconsciously avoid eating
dairy products, thus making a diagnostic history more obscure. In others,
symptoms may simulate irritable bowel syndrome.
The
diagnosis may be suspected if acidic stools (pH lower than 6) are passed or if,
after a glass of milk, the patient develops abdominal cramps, distension and
watery diarrhoea within 20 to 30 min. It is further substantiated by an oral
lactose tolerance test, and can be absolutely confirmed by the finding of low
lactase activity in a bowel biopsy specimen.
The disorder is readily controlled
by a lactose-free diet, or often simply by avoiding milk drinks. A child who
lacks the enzyme lactase can absorb fructose. If a lactose-free diet is
continued, oral calcium supplements should be given.
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