The authors concluded: “Our study shows how in later prehistoric times, as populations and settlements grew, human health would have been increasingly compromised by poor sanitation and increasing diarrheal diseases, especially those of animal origin.
“Under these conditions, consuming milk would have led to increased mortality rates, with individuals without lactase persistence being particularly vulnerable.”
About 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, with most adults being unable to drink milk 5,000 years ago without any discomfort.
But today’s obsession with our food allergies and intolerances has led to an increase in the popularity of non-dairy products, such as pea, potato, soy and almond milk, as well as lactose-free cheese and non-dairy ice cream.
However, new data suggests they are most likely not needed, as people with lactose have been consume milk and dairy for millennia with no real problem.
Human babies make an enzyme called lactase, which allows them to break down the sugar in milk and dairy — lactose — to make energy.
In people with lactose intolerance, this ability is lost in childhood and they cannot break down sugar naturally. People who are supposedly “lactose persistent” retain the ability and can break down dairy throughout their lives.
It was long thought that this ability arose through natural selection, because it would be useful to be able to consume milk.
This was because prehistoric humans may have had to drink large amounts of milk from cattle when drinking water was scarce.