Parents often urge children to drink milk for stronger bones, and for good reason it turns out.
Drinking milk may have made ancient humans taller and heavier, researchers have said.
They analysed skeletons from archaeological sites spread over a period of 25,000 years and found that milk led to humans increasing in size between 7,000 and 2,000 years ago.
The size increase took place in areas where people had genes that enabled them to drink milk, the scientists said.
In some areas, ancient humans had higher levels of genes that allowed the production of enzymes – called lactase persistence – that digest milk into adulthood.
Dr Eoin Parkinson, from the School of Natural and Built Environment's department of archaeology and palaeoecology at Queen's University Belfast, said: "Through this study we've found that drinking milk led to increased skeletal growth and taller populations in some parts of the world.
"Everyone probably has memories from their childhood of being told to drink up their milk to help them grow.
"We can almost think of this in the context of our own evolutionary story and we see trends in dairy consumption going back as far as 7,000 years ago having an impact on how people process dairy products today.
"Drinking milk and the consumption of dairy products is a vital component in food culture in many parts of the world, so it is interesting to understand the underlying biological processes related to these practices."
He added: "Agriculture emerged in the Near East before farming groups migrated into Europe, bringing a host of new domesticated plants and dairy-producing animals with them.
"In some parts of northern and central Europe, where local environments were not suited to the newly imported south-west Asian crops, human societies responded through increased consumption of milk."
The study, involving a team of 16 researchers, compared the stature and body mass of 3,507 skeletons from 366 different archaeological sites.
This created a large comparative data set to examine human body variation over time and geographic location.
The data set used in the study was primarily based on European samples, due largely to historically more frequent archaeological exploration within the continent.
Farming developed in different regions independently and migrating farmers brought crops and dairy animals with them to parts of Eurasia occupied by hunter-gatherers.
The ability to digest higher quantities of lactose led to greater energy availability from dairy products.
The legacy of ancient milk consumption is still evident today, through different frequencies of lactose intolerance in populations.
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