Forebears had lactose issues but didn’t milk it

Dairy products consumed without complaint 9,000 years before most humans evolved gene to digest them

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 study shows that lactose intolerant people have been drinking milk for more than 9,000 years without significant health issues.

Scientists say the inability 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 (UCL) 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,” Prof Mark Thomas of UCL told the journal Nature.

The team of scientists 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.

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 the intolerance could prove fatal as severe symptoms caused deadly dehydration and other gastrointestinal problems.

It was during these periods 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, and 284 times more likely in times of disease.

“If you are healthy and lactase nonpersistent, and you drink lots of milk, you may experience some discomfort, but you are not going to die of it,” said Prof George Davey Smith, of Bristol University. “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 highlactose milk – exactly when they shouldn’t. Under these conditions consuming milk would have resulted in increasing death rates, with individuals lacking lactase persistence being especially vulnerable.”

About one in 10 people in Britain are 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 unable to drink milk without some discomfort 5,000 years ago.