Early on when I started experiencing digestive issues, my doctor proposed that I might have lactose intolerance. I wondered, how does one become lactose intolerant as an adult and why does it only occur for some people and not others. Although in the end I am able to process dairy, this thought has lingered so I decided to do some research on this topic.
Lactose is a sugar in milk and other dairy products that requires the enzyme lactase present in our small intestine to break it into the two sugars, glucose and galactose. This allows the sugars to be absorbed and used by our bodies. If we are deficient or have less lactase, then the lactose cannot be broken down and absorbed and instead enters our large intestine (colon) where bacteria feeds off of it and leads to the not so fun consequences of lactose intolerance.
Since the beginning of time, babies have been born with lactase present to aid in the digestion of their mother’s milk. The exceptions are with babies who because of genetics are born without lactase and premature babies born before the third trimester when lactase is produced. Premature babies will eventually produce the lactase needed to digest milk. Lactose is turned off or reduced resulting in lactose intolerance beginning at 2 years old in some cases or during adulthood in others. For some people, lactase is never turned off and they can drink milk with no problems. The reduction of lactase can be due to its gene being turned off, infection in the small intestine, bacterial overgrowth, or damage to the small intestine caused by celiac or Crohn’s disease.
More than 10,000 years ago, very few or no adults were lactose tolerant, whereas now 35% of adults are lactose tolerant. Our ancestors got their calcium and vitamin D, which is needed to help absorb calcium, through eating yogurt and cheese. The yogurt was made by milk, taken from an animal in the morning and being left out in the warm weather until the afternoon. Additionally, there was the discovery of pottery by archaeologists being used as sieves to separate the milk solids from the whey indicating how cheese was made. Both yogurt and cheese use lactose up in their fermentation process that made us able to digest them, which is still the case today for many people.
Sometime around 8,000 years ago in Turkey, it is thought that a genetic mutation occurred in the people living there that allowed the production of lactase, enabling this population, older than 2 years old, to digest milk. The migration of this group to Europe increased the number of people with this mutation and how many people could drink milk into adulthood without getting sick. There is still no explanation for why this mutation happened but the 35% of adults who are lactose tolerant are happy it did. Luckily, there are now so many good lactose free products that allow the rest of, and the majority of, the world population to still have their ice cream cake and eat it too.
1. Lactose Intolerance. Medicinenet.com
2. Lactose Intolerance. National Institute of Diabetes and Digestive and Kidney Diseases
3. Lactose Intolerance. Medline Plus
4. Lactose Tolerance and Human Evolution. Smithsonian.com, 4/7/09
5. The most spectacular mutation in recent history. How did milk help found western civilization? Slate, 10/2012
6. Archaeology: The Milk Revolution. Nature, 7/31/13
7. An evolutionary whodunit: How did humans develop lactose intolerance? NPR: The Salt, 12/27/2012
Photo found on PEXELS