Scientists Say: Lactose

This is a sugar found in milk and other dairy products


Milk contains a natural sugar called lactose.


Lactose (noun, “LACK-toes”)

This is a sugar molecule. It’s found in milk and other dairy products, such as cheese and yogurt. For the human body to digest lactose, the sugar molecule must be broken down into smaller molecules. Lactose is broken down by an enzyme — a molecule that speeds up chemical reactions — called lactase. Nearly everyone is born with the ability to produce this enzyme. It’s what allows mammals to drink milk from their mothers. However, people can stop producing the enzyme as they grow up. About 65 percent of adults can’t digest lactose well — or at all — after childhood. This includes many people of East Asian, West African, Greek and Italian descent. Without lactase, a person who eats dairy products with lactose can experience stomach pain, gas and bloating.

In a sentence

Scientists have found that even people from the Stone Age could have been lactose intolerant.  

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Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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