What is lactose intolerance? Our major source of lactose is milk (cow, goat, sheep, domesticated buffalo, camel and human) or yogurt. It is not found in hard cheese or butter. When we are born, we have a digestive enzyme called lactase to break down lactose in breast milk to its constituent sugars, glucose and galactose, which are then absorbed into the blood.
By the age of five, many people no longer produce their lactase enzyme and can’t digest lactose any more. For them, large amounts of lactose can cause intestinal cramping because gut bacteria convert the lactose to gas and lactic acid. Not comfortable. They are now lactose intolerant.
Why some of us can continue drinking milk after early childhood Scientists have been able to check DNA from around the world and by marrying their findings to human history (who lived where, when), have given us a better understanding why some of us can enjoy milk and yogurt and ice-cream right throughout our lives and others can’t.
Around 10,000 years ago, when humans started to keep cattle as a beasts of burden and a source of meat, the ability to handle lactose in adulthood was absent. However, at some point over the next thousand years or so, a mutation occurred which allowed some people to be able to drink milk well past their fifth birthday and on into adulthood. Researchers who have studied the DNA from skeleton remains in central Europe, report that about 80% of people in this area had the mutation for tolerating lactose about 7000 years ago. This is a rapid spread of a mutation, strongly suggesting that it offered a survival advantage to milk drinkers, according to a new book (and a really terrific read), The 10,000 Year Explosion – How Civilization Accelerated Human Evolution (Gregory Cochran & Henry Harpending).
Over time, the mutation became more dominant in parts of Europe through to northern India. It is thought the mutation occurred independently in parts of Arabia when the camel became domesticated and camel milk became part of the local diet.
In fact, being able to tolerate lactose in the diet, allowed the expansion of Indo-Europeans, tracked by both the spread of lactose tolerance and the Indo-European languages (e.g. Spanish, English, Hindi, Portuguese, Russian, German, French). Put another way, if your native language was Indo-European in origin, then there was a good chance you could handle lactose over the last 7000 years or so. It also explains why eastern and southern Asia, Japan, parts of Africa and the indigenous folk of Australia have both a very different language background and the inability to handle lactose after being weaned.’
Glenn’s complete article is HERE.