What causes lactose intolerance?

Source: Your Body Your Health, Reader’s Digest

Some people are unable to consume dairy products without experiencing abdominal discomfort and bloating along with nausea and diarrhea two to three hours afterwards. These people are described as having lactose intolerance ‘ a situation in which the gut is unable to break down the sugar in cow’s milk, known as lactose.

What are the causes of lactose intolerance?

In order for lactose to be digested and absorbed from the gut, it must be broken down into its two constituent sugars, glucose and galactose. The enzyme responsible for this breakdown process is lactase, which is found in the cells lining the small intestine.

For adults in the majority of the world’s ethnic groups, lactose intolerance is the norm. The ability to produce lactase is lost at weaning, but this does not generally cause problems because dairy products are largely absent from the diet in such cultures. In the Western world, however, where dairy products feature heavily in the normal diet and populations tend to have mixed ethnic backgrounds, the picture is more complicated. Ethnic groups such as Native Americans, Afro-Caribbeans and Asians often retain the tendency to be lactose intolerant. Caucasians normally retain the ability to produce lactase after weaning, but even within this group many people develop lactose intolerance for one of two reasons.
‘ Some babies are born with a complete absence of lactase in the gut ‘ a congenital condition called alactasia.
‘ In others, who initially produce lactase normally, the levels drop with increasing age. A diet rich in dairy products or a significantly reduced level of lactase can give rise to symptoms in such cases.

What are the symptoms of lactose intolerance?

Babies with alactasia develop the following symptoms immediately they are fed with cow’s milk products:
‘ vomiting;
‘ colic;
‘ failure to gain weight.

People who develop lactose intolerance later in life will notice bloating, discomfort and diarrhoea occurring as the undigested lactose is broken down by the gut bacteria.

How is it diagnosed?

Lactose tolerance testing used to be the standard method used to diagnose the condition, but is rarely performed now. The patient fasts for eight hours and is then given a dose of lactose. Blood samples are then taken at regular intervals to measure blood glucose (sugar) levels. If levels do not rise, this indicates that the lactose is not being broken down. Alternatively, the patient may be administered a modified version of this test, using a dose of lactose labelled with hydrogen. In lactose intolerance, the hydrogen can then be detected on the patient’s breath.

Up to 90 percent of Asians and Afro-Caribbeans are lactose intolerant, compared with about 12 percent of Caucasians.

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