According to scientists, the inability to digest lactose would have posed little problems to people in good health in ancient times. Photo / Getty Images
According to scientists, the inability to digest lactose would have posed little problems to people in good health in ancient times. Photo / Getty Images
A flat white with soy or oat milk has become a common coffee order among millennials, with many citing lactose intolerance for their dairy avoidance.
But a new study shows that lactose intolerant people have been drinking milk for more than 9000 years without significant health issues.
Scientists say theinability to digest lactose would have posed very few problems to ancient people in good health, simply causing some minor discomfort and digestive symptoms.
Researchers from University College London and the University of Bristol suggest the ability to tolerate milk developed in healthy people who survived famine and disease.
"It's probably the most strongly selected single gene trait to have evolved in Europeans and also in many African and Middle Eastern and Southern Asian populations over the last 10,000 years," said Professor Mark Thomas, professor of Evolutionary Genetics at the University College London.
The study, published in Nature, touts that people have been drinking milk for millenia even if the symptoms are suboptimal.
A team of academics gathered historical data on how much milk was drunk around the world at various times and compared this to when the lactase gene was common.
People consuming soy or oat milk has become common, with many citing lactose intolerance for their dairy avoidance. Photo / Getty Images
They found that there was no link between the two, confirming that drinking milk and being able to digest lactose was of no evolutionary benefit.
However, the evidence did show that during times of famine and disease, when a person was likely to be under more physical stress, the intolerance could prove fatal as severe symptoms caused deadly dehydration and other gastrointestinal problems.
It was at these periods of time, the scientists say, that the prevalence of the lactase gene shot up.
The lactase gene was 689 times more likely to be found in a person during times of famine, the researchers found, and 284 times more likely in times of disease.
"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," said Professor George Davey Smith, director of the MRC Integrative Epidemiology Unit at the University of Bristol and a co-author of the study.
"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."
The lactase gene was 689 times more likely to be found in a person during times of famine, and 284 times more likely in times of disease. Photo / Getty Images
The authors concluded: "Our study demonstrates how, in later prehistory, as populations and settlement sizes grew, human health would have been increasingly impacted by poor sanitation and increasing diarrhoeal diseases, especially those of animal origin.
"Under these conditions consuming milk would have resulted in increasing death rates, with individuals lacking lactase persistence being especially vulnerable."
Around one in 10 Britons are lactose intolerant today, 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 5000 years ago unable to drink milk without some discomfort.
But the modern-day obsession with our food allergies and intolerances has led to a surge in popularity of non-dairy foods, such as pea, potato, soy and almond milks, as well as lactose-free cheese and non-dairy ice cream.
However, new data show they are most likely unnecessary, as lactose people have been consuming milk and dairy for millenia without real issue.
Human babies make an enzyme called lactase, which allows them to break down the sugar in milk and dairy - lactose - to make energy.
In lactose intolerant people, this ability is lost in childhood and they are unable to break down the sugar naturally. People who are so-called "lactose persistent" keep the ability and can break down dairy all their life.
It was long thought that this ability emerged via natural selection, because it would be beneficial to be able to consume milk.
This was because prehistoric people may have had to drink large amounts of milk from cattle when drinking water was scarce.
