Study Finds Humans Developed Lactose Tolerance During Famines and Disease Outbreaks

A new study has found that our ability to enjoy dairy delicacies today may be due to the sacrifice of our ancestors who died of disease and starvation thousands of years ago.

It was previously thought that the genetic variation that allows humans to digest lactose arose at the same time that we started drinking animal milk.

This is because the gene prevented unpleasant symptoms of lactose intolerance, such as diarrhea.

However, a new study by scientists from the University of Bristol and University College London (UCL) suggests that the variation arose later, during famine and contagious diseases.

During these periods, when people were already weakened by hunger or disease, drinking milk could prove fatal to those who suffered from lactose intolerance.

As a result, individuals carrying the lactose tolerance gene were more likely to survive and pass the gene on to their offspring, increasing its prevalence in society.

“When people are severely malnourished, diarrhea can go from a nuisance to a deadly condition,” explained Mark Thomas, a professor of evolutionary genetics at the University of California.

It is known that people began to domesticate animals and consume their milk about 10,000 years ago. At that time, all people could not digest lactose, the main sugar in milk, after they were weaned from breastfeeding. However, since then, the prevalence of a genetic variation that allows the body to digest lactose has increased.

Symptoms of lactose intolerance can be life-threatening if they occur at the same time as fasting or an infectious diarrheal disease.  People without the LP genetic variation are more likely to be affected by this combination than people with it, and therefore less likely to pass on their genes.

Symptoms of lactose intolerance can be life-threatening if they occur at the same time as fasting or an infectious diarrheal disease. People without the LP genetic variation are more likely to be affected by this combination than people with it, and therefore less likely to pass on their genes.

It is known that people began to domesticate animals and consume their milk about 10,000 years ago.

At that time, all people could not digest lactose – the main sugar in milk – after they were weaned from breastfeeding.

The enzyme that breaks down lactose is called lactase, and it is produced in the small intestine during fetal development.

After they stopped breastfeeding, their bodies stopped producing lactase, so they could no longer digest lactose from dairy products.

Thus, sugar can enter the colon and cause symptoms of hypolactasia or lactose intolerance, including cramps, bloating, diarrhea, and flatulence.

However, since then, the prevalence of a genetic variation that continues to produce lactase in the body has increased.

This variant is known as lactase persistence (LP), which is found in about a third of all adults today.

Until a new study published today in NatureIt was believed that the prevalence of LP increased when people began to consume dairy products regularly.

Milk and its products contain healthy calories — minerals like calcium and many micronutrients — so consuming them gives them a nutritional advantage.

Thus, it was assumed that LP variations were transmitted through natural selection; where more people with the LP gene passed on their genes to their offspring than people without it.

Now, however, researchers have discovered that milk consumption was common thousands of years before the LP gene began to spread.

To come to this conclusion, milk fat residues ingested by shards of unglazed earthenware used by ancient farmers were studied to determine when the population began to consume milk.

They showed that European farmers harvested milk almost 9,000 years ago, but this increased and decreased in different regions at different times.

WHY ARE SOME PEOPLE LACTOSE INTOTOLE?

When people started consuming milk, they were all lactose intolerant.

The enzyme that breaks down lactose is called lactase, and it is produced in the small intestine during fetal development.

After babies stopped breastfeeding, their bodies stopped producing lactase, so they could no longer digest lactose after eating dairy products.

Thus, sugar can enter the colon and cause symptoms of lactose intolerance, such as bloating and diarrhea.

About 5,000 years ago, people began to develop a gene that continued the production of lactase.

This is thought to be because hunger and disease are life-threatening, combined with the symptoms of lactose intolerance, which is why the gene allowed humans to survive and pass it on to their offspring.

Now this gene is found in about a third of all adults.

Ancient DNA was also analyzed to see when the LP gene arose and increased in frequency, as well as modern DNA databases that link it to health effects.

While this showed that the LP variation first arose about 5,000 years ago, ancient DNA showed no connection between changes in milk intake over time and natural selection for lactase resistance.

Modern DNA data showed that there were only small differences in milk consumption between people with lactase intolerance and intolerance.

There were also no big differences between them in symptoms and health outcomes, such as bone density and vitamin D levels.

Therefore, it is unlikely that the gene variation arose because it allowed people to digest dairy products without symptoms of lactose intolerance if they were so mild.

The researchers then ran statistical modeling to establish which environmental factors actually stimulated LP in ancient populations.

This included using population size as an indicator of the threat of famine, as more mouths needed to be fed.

Population density was used as an indicator of the risk of infectious diseases, as a denser population meant that bacteria could spread more quickly.

The patterns of these factors were found to correlate with the growth of the LP gene.

This is because the symptoms of lactose intolerance can be life-threatening if they occur at the same time as fasting or an infectious diarrheal disease.

People without the LP genetic variation are more likely to be affected by this combination than people with it, so people with LP are more likely to survive and pass on the gene.

“When their crops were lean, prehistoric humans were more likely to consume high-lactose unfermented milk — just when they shouldn’t have,” said Professor George Davey Smith, director of the MRC’s Integrative Epidemiology Unit at the University of Bristol.

The authors concluded: “The same factors that influence human mortality today seem to have driven the evolution of this amazing gene in prehistoric times.”

The fact that the actual symptoms of lactose intolerance are so mild raises the question of whether some people who believe they suffer from it can actually enjoy milk.

The fact that the actual symptoms of lactose intolerance are so mild raises the question of whether some people who believe they suffer from it can actually enjoy milk.

The results of the study show that it is difficult to tell if a person has the LP variant, since the symptoms of lactose intolerance can be very mild.

The bodily reactions often attributed to lactose intolerance are also easily confused with those of other functional bowel disorders.

So the question arises as to whether some people in the UK who believe they are lactose intolerant can actually enjoy milk and cheese.

Professor Thomas said: “Lactose intolerance is often blamed when in fact people are allergic to cow’s milk.

“Milk is extremely nutritious, so cutting out milk can be a loss to the diet.”

THE GREAT MIGRATION OF THE BRONZE AGE WAS FUEL WITH MILK

A recent study showed that Bronze Age migrations lived on milk.

According to researchers, migrants from Russia brought lactose tolerance genes to Europe.

During the last ice age, milk was a toxin for adults because, unlike children, they couldn’t produce the enzyme needed to break down lactose.

But when agriculture began to replace hunting and gathering in the Middle East about 11,000 years ago, shepherds learned to reduce lactose levels to manageable levels by fermenting milk to make cheese or yogurt.

Read more: Great Bronze Age migration fed on milk

At the beginning of the Bronze Age, the mass migration of people from the steppes of Russia undertook a series of journeys that changed the course of history.  Now a new analysis of tartar (pictured) has revealed that the secret to their success was quite simple: They drank milk.

At the beginning of the Bronze Age, the mass migration of people from the steppes of Russia undertook a series of journeys that changed the course of history. Now a new analysis of tartar (pictured) has revealed that the secret to their success was quite simple: They drank milk.