In New Zealand, we drink a lot of milk, so you might be surprised to learn that most adults in the world are lactose intolerant and can’t consume dairy products.
Inheriting lactose intolerance
The ability to digest milk or milk products is inherited from our parents. All babies drink milk, but after they’re weaned, some lose the ability to drink milk without feeling ill. This is known asintolerance.
If you are lactose intolerant and you drink a glass of milk, you may become nauseous or have stomach cramps, bloating and diarrhoea. The amount of milk that causes this reaction varies from person to person.
Causes of lactose intolerance
Lactose is a sugar that occurs naturally in milk and most dairy products. Lactose is readily broken down in the gut by ancalled lactase. Babies produce large amounts of lactase until they are weaned.
After about 5 years of age, most people (about 75% of the world’s population) stop producing the lactase enzyme. Without lactase, they can no longer digest milk, and they become lactose intolerant. Typically, people who originate from Africa, Asia or the Pacific stop producing the lactase enzyme after weaning and can’t consume milk or milk products in adulthood. However, there are a number of biotechnology solutions developed to help people who are lactose intolerant to consume dairy products.
Find out more about treating lactose intolerance.
Lactose intolerance is a recessive trait
is a disorder. For a recessive disorder to show, both copies of the , called alleles, have to be identical. Individuals who have a cytosine (C) on both alleles close to the lactase gene do not produce lactase in adulthood and are lactose intolerant.
Genetic mutation helps digest lactose
So how do most New Zealanders consume milk without feeling ill? A single point mutation in thenear to the lactase gene changes the cytosine (C) to a thymine (T). Individuals who have the thymine (T) nucleotide are lactose tolerant and can digest milk products in adulthood.
People who can digest lactose often originate from northwest Europe (like many New Zealanders) and some parts of Africa. Thethat allows them to do this arose relatively recently, about 12,000–10,000 years ago, as farming became a major source of food.
Find out more about a
Ask a geneticist about inheriting lactose intolerance - information about lactose intolerance written for high school students by The Tech Museum of Innovation, California, US
Find out more about lactose intolerance, including the amount of lactose in milk products.
A summary of data from foodreactions.org showing the percentage of people with lactose intolerance in different world regions.