The authors concluded: “Our study demonstrates how, in later prehistory, as populations and settlement sizes grew, human health would have been increasingly affected by poor sanitation and increased diarrheal diseases, especially those of animal origin.
“Under these conditions, consuming milk would have resulted in increased mortality rates, and individuals who lack lactase persistence are particularly vulnerable.”
Around one in ten Britons today is lactose intolerant, but this figure is as high as two-thirds elsewhere in the world. The level of lactose intolerance has decreased over time, and most adults 5,000 years ago could not drink milk without discomfort.
But today’s obsession with our food allergies and intolerances has led to a rise in the popularity of non-dairy foods, such as pea, potato, soy and almond milk, as well as lactose-free cheese and dairy-free ice cream.
However, new data shows that they are probably unnecessary, as people with lactose intolerance have been consuming milk and dairy products for millennia with no real problems.
Human babies make an enzyme called lactase, which allows them to break down milk and dairy sugar – lactose – to produce energy.
In lactose intolerant people, this ability is lost during childhood and they are unable to break down sugar naturally. People who are called “lactose intolerant” retain the ability and can break down dairy throughout their lives.
For a long time it was thought that this ability arose through natural selection, because it would be beneficial to be able to consume milk.
This was because prehistoric people may have had to drink large quantities of milk from cattle when drinking water was scarce.