Lactose intolerance is the common term used to describe a problem with a person’s ability to digest lactose, and it is most often caused by a lack or deficit of the lactase enzyme in the person’s small intestine. What many people might not know is that there is a genetic component to lactose intolerance that most likely evolved due to the domestication of dairy-producing livestock.
Learn more about the science and the symptoms related to this common trait:
What is lactose?
In short, lactose is a sugar that’s composed of galactose and glucose subunits and has the molecular formula C12H22O11. Lactose makes up around 2-8% of milk and is found in dairy products such as cheese, milk, and butter.
What is the usual role of lactose in development?
For mammals (a group which of course includes humans), newborns usually subsist solely on the mother’s milk early in life and then are weaned from milk entirely. Because of this, mammals have evolved with systems that generally turn off of lactase expression after weaning.
What causes lactose intolerance?
As mammals who have evolved with the same propensities, most humans start to show decreased levels of lactase expression in childhood, and are often unable to digest more than small amounts of lactose. This inability to digest moderate or high amounts of lactose is called lactose intolerance, and the related trait is known as lactase non-persistence.
How common is lactose intolerance globally?
Although the majority of the global population has some level of lactose intolerance, there are quite a few lucky people who are still able to process lactose well into adulthood, avoiding the common (and unpleasant) symptoms of lactose intolerance, including cramps, bloating, and diarrhea.
Is genetics involved?
Research has shown that there is indeed a genetic component to lactase persistence (which manifests as lactose intolerance) is a dominant trait that is inherited, and this inheritance keeps some populations from generally having these issues with lactose consumption.
In general, lactose intolerance is shown in most of the world’s populations outside of people with northern European ancestry, as well as other pockets of populations, particularly nomadic groups who roamed with cattle and other milk-producing livestock.
How and where did it evolve?
The difference between lactase tolerance within populations seems to be related to an adaptive response to the domestication of dairy animals, which would explain why people who historically tended these animals and drank their milk as adults evolved with a lactose-persistence mutation.
What are the symptoms?
Symptoms can vary from person to person, and can be from mild to severe depending on how much lactase your body makes. Symptoms usually begin 30 minutes to 2 hours after you consume dairy products. The symptoms may include:
- Pain or cramps
- Rumbling sounds in your belly
- Loose stools or diarrhea
How can you test for lactose intolerance?
- Hydrogen breath test: this is the most common type of test. Your doctor will instruct you to drink a liquid solution containing lactose. You will then breath into a HBT Sleuth hydrogen monitor at set intervals to determine how much hydrogen there is in your body.
- Lactose tolerance test: same as hydrogen test, you are required to drink a liquid with lactose. After two hours, the doctor will take a blood sample to measure how much glucose is in your blood. If your glucose levels don’t rise, it means your body isn’t properly digesting and absorbing the lactose-filled drink.
- Genetic testing: genetic testing such as our OmeHealth DNA test can help you determine your genetic predispositions relating to lactose intolerance.