Whether in your fully loaded mac and cheese, ham toastie or a double shot choco mocha with extra sprinkles, most of us take consuming dairy as a normal part of our everyday lives. Even though some of us can’t digest lactose – the sugar found in dairy. How did this come to be?
A study carried out by scientists from the University of Bristol and University College London, tracing human’s dairy consumption for more than 9,000 years, has found that it turns out that our love of dairy may be down our ancestors’ exposure to famine and disease.
“To digest lactose we need to produce the enzyme lactase in our gut. Almost all babies produce lactase, but in the majority of people globally that production declines rapidly between weaning and adolescence,” said the study’s co-author Prof George Davey Smith, from the University of Bristol.
“However, a genetic trait called lactase persistence has evolved multiple times over the last 10,000 years and spread in various milk-drinking populations in Europe, central and southern Asia, the Middle East and Africa. Today, around one third of adults in the world are lactase persistent.”
By computer analysing the pattern of milk and dairy consumption of humans over the last 9,000 years, based on ancient DNA studies, data from the UK Biobank, and archaeological data, the team were able to show that the lactase persistence genetic trait only emerged in around 1,000 BC.
“The lactase persistence genetic variant was pushed to high frequency by some sort of turbocharged natural selection. The problem is, such strong natural selection is hard to explain,” said co-author Prof Mark Thomas of University College London.
To study how lactose persistence evolved, the team gathered together 7,000 organic animal fat residues from more than 13,000 fragments of pottery found in 500 archaeological sites dating back to the earliest farming communities almost 9,000 years ago.
They found that the use of dairy products fluctuated throughout European prehistory and that the presence of the lactase persistence genetic variant occurred around 5,000 years ago.
However, they say that the consumption of dairy was likely high in times of famine or disease for survival – even in the lactose intolerant, despite the unfortunate effects.
“Our findings show milk use was widespread in Europe for at least 9,000 years, and healthy humans, even those who are not lactase persistent, could happily consume milk without getting ill.
“However, drinking milk in lactase non-persistent individuals does lead to a high concentration of lactose in the intestine, which can draw fluid into the colon, and dehydration can result when this is combined with diarrhoeal disease, said Prof Smith.
“If you are healthy and lactase non-persistent, and you drink lots of milk, you may experience some discomfort, but you not going to die of it. However, if you are severely malnourished and have diarrhoea, then you’ve got life-threatening problems. When their crops failed, prehistoric people would have been more likely to consume unfermented high-lactose milk – exactly when they shouldn’t.”