How is lactose
Lactose intolerance can be hard to diagnose based on
symptoms alone. People sometimes think they suffer from lactose
intolerance because they have the symptoms associated with the
disorder, not knowing other conditions such as irritable bowel
syndrome can cause similar symptoms. A doctor can use tests to
diagnose lactose intolerance but may first recommend
eliminating cow’s milk from the diet to see if the symptoms go
The most common tests used to measure the absorption of
lactose in the digestive system are the lactose tolerance,
hydrogen breath, and stool acidity tests.
- The Lactose Tolerance Test. This test
requires fasting (not eating) before the test and then
drinking a liquid that contains lactose. Several blood
samples are then taken over a 2-hour period to measure the
person’s blood glucose (blood sugar) level. These measures
indicate how well the body is able to digest lactose.
Normally, when lactose reaches the digestive system, the
lactase enzyme breaks it down into glucose and galactose.
The liver then changes the galactose into glucose, which
enters the bloodstream and raises the person’s blood
glucose level. If, however, lactose is incompletely broken
down, the blood glucose level does not rise and a diagnosis
of lactose intolerance is confirmed.
- The Hydrogen Breath Test. This test
measures the amount of hydrogen in a person’s breath. Very
little hydrogen is normally detectable. However, undigested
lactose in the colon is fermented by bacteria and produces
various gases, including hydrogen. The hydrogen is absorbed
from the intestines, carried through the bloodstream to the
lungs, and exhaled. In this test, the person drinks a
lactose-loaded beverage and the breath is analyzed at
regular intervals. Raised levels of hydrogen in the breath
indicate improper digestion of lactose. Certain foods,
medications, and cigarettes can affect the accuracy of the
test and should be avoided before taking the test. People
should check with their doctor to make sure they are not
taking medications that may interfere with test
The lactose tolerance and hydrogen breath tests are not
given to infants younger than 6 months of age. A large lactose
load can be dangerous prior to this age, as infants are more
likely to become dehydrated from diarrhea that can be caused by
- Stool Acidity Test. This test may be
used for infants and young children to measure the amount
of acid in their stool. Undigested lactose fermented by
bacteria in the colon creates lactic acid and other fatty
acids that can be detected in a stool sample. Glucose may
also be present in the sample as a result of unabsorbed
lactose in the colon.
What causes lactose
Some causes of lactose intolerance are well known. Primary
lactase deficiency is a condition that develops over time.
After about age 2 the body begins to produce less lactase,
though most people will not notice symptoms until they are much
Secondary lactase deficiency occurs when injury to the small
intestine or certain digestive diseases reduce the amount of
lactase a person produces. These diseases include celiac
disease, inflammatory bowel disease, and Crohn’s disease.
Researchers have identified a genetic link for lactose
intolerance. Some people are born with a likelihood of
developing primary lactase deficiency because it has been
passed to them genetically (inherited from their parents). This
discovery may be useful in developing a diagnostic test to
identify people with the condition.
How is lactose
Lactose intolerance is easy to treat. No treatment can
improve the body’s ability to produce lactase, but symptoms can
be controlled through diet.
Young children and infants with lactase deficiency should
not consume lactose-containing formulas or foods until they are
able to tolerate lactose digestion. Most older children and
adults do not have to avoid lactose completely, but people
differ in the amounts and types of foods they can handle. For
example, one person may have symptoms after drinking a small
glass of milk, while another can drink one glass but not two.
Others may be able to manage ice cream and aged cheeses, such
as cheddar and Swiss, but not other dairy products. People can
also tolerate more lactose by having smaller amounts of it at
one time. The level of dietary control needed with lactose
intolerance depends on how much lactose a person’s body can
For those who react to very small amounts of lactose or have
trouble limiting their intake of foods that contain it, the
lactase enzyme is available without a prescription to help
people digest foods that contain lactose. The tablets are taken
with the first bite of dairy food. Lactase enzyme is also
available as a liquid. Adding a few drops of the enzyme makes
lactose more digestible for people with lactose
Lactose-reduced milk and other products are available at
most supermarkets. The milk contains all of the nutrients found
in regular milk and remains fresh for about the same length of
time, or longer if it is super-pasteurized.