Lactose intolerance facts for kids

Kids Encyclopedia Facts
Pig lactation
Baby mammals drink milk

Lactose intolerance is when a person cannot digest milk or milk products (such as cheese or yoghurt).

Lactose is a disaccharide sugar (double sugar molecule), which must be split (digested) into two simple sugars (monosaccharides), glucose and galactose.

An enzyme called lactase is needed to break it down. People with lactose intolerance do not have this enzyme or make only small quantities. Because of this they are unable to digest lactose.

Up to 75% of people worldwide begin to lose the ability to digest lactose as they grow into adults. This loss of ability ranges from 5% in northern Europe, to over 71% in Sicily and to over 90% in parts of Africa and Asia. There is no cure for lactose intolerance. People need to change their diet to only include food with very little lactose. There are many milk substitutes.

Milk is not a fermented product. If is not digested, then it may ferment in the small intestine which can cause a problem called pseudoallergy. Amino acids are changed to other substances, which may act in much the same way as histamine in a true allergy.

Lactose intolerance is not the same as milk allergy, which is an immune reaction to some of the proteins in milk.

Lactase evolution in humans

Normally infant mammals drink their mother's milk. Then the gene which causes the body to make lactase is switched off, and the young move on to adult food. They can no longer digest milk.

Humans are somewhat different from other mammals. Some humans continue to produce lactase, and some do not. It is a type of genetic polymorphism.

The ability to digest lactose into adulthood ('lactase persistence') was useful to humans after the invention of animal husbandry. People kept animals which could provide milk.

Hunter-gatherer people before the Neolithic revolution were mostly lactose intolerant. So are modern hunter-gatherers.

Genetics

A mutation on chromosome 2 stops the shutdown in lactase production. This makes it possible for those with the mutation to continue drinking fresh milk (and eating other dairy products) throughout their lives.

This appears to be a recent adaptation to dairy products. It occurred in both northern Europe and east Africa in people with a historically pastoral lifestyle. Lactase persistence, allowing lactose digestion to continue into adulthood, is a dominant allele, making lactose intolerance a recessive trait.

Genetic studies suggest that the oldest mutations associated with lactase persistence have only become common in human populations in the last 10,000 years. Because of this, lactase persistence is often given as an example of recent human evolution. As lactase persistence is genetic, but animal husbandry a cultural trait, this is geneculture coevolution.

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Lactose intolerance Facts for Kids. Kiddle Encyclopedia.