Why is Lactose Intolerance Such a Common Digestive Disorder

 by  Isabella Frobisher

What is Lactose Intolerance?

Lactose malabsorption, which around 68% of the world's population has, can lead to the commonly known digestive disorder of lactose intolerance. However, the majority of this number only become lactose intolerant when they reach adulthood. Lactose intolerance is when people are unable to fully digest the lactose (sugar) in milk as there isn't enough lactase produced by your small intestine. Symptoms include bloating and/or feeling nausea after eating or drinking dairy products or in severe cases diarrhoea. Lactose intolerance can lead to you not getting enough nutrients such as Vitamin D and calcium. Vitamin D is essential for keeping your bones, teeth and muscles healthy and calcium is essential for growth and to have healthy bones. Hence, if it does become the case that you aren't getting enough of these vital vitamins, you may need to change your diet or take vitamin pills. However, this is only in extreme cases. Additionally, if you are lactose intolerant it doesn't mean that you are unable to consume dairy products, it just means that you need to be aware of how much of these products you are consuming and the effect they are having on your body. 

How should dairy products be naturally digested?  Dairy products in a lactose tolerant person should be digested by the lactase turning the lactose into two simple sugars - glucose and galactose. These are then absorbed into the bloodstream through the intestinal lining. Whereas, in a lactose intolerant person the lactose moves into your colon instead of being absorbed and digested, causing the uncomfortable symptoms as the lactase is not properly digested.

Why do so many people suffer from this intolerance? Around several thousand years ago, a genetic mutation occurred in a small group of people in Europe or Western Asia, enabling them to produce lactase to digest lactose from cow’s or goat’s milk that they drank. This mutation was then passed down each generation and is now present today amongst around a third of the world's population. Those with this mutation are the lactose tolerant people in today’s society.

Elsewhere in the world at this time, the mutation did not occur as milk-based products were rarely consumed as they were not part of the daily diet. However, a small minority of this group naturally did process the ability to digest dairy products. But as milk wasn’t a key feature of the daily diet in certain areas such as Asia and America, the majority did not process this genetic mutation as it wasn't seen as a genetic advantage to be able to consume milk. Therefore, the mutation genes never propagated throughout the population and no genetic mutations were passed down each generation. Those without this mutation are the lactose intolerant people in today's society.

The fact that now only around a third of the world population can digest lactose is an example of genetic evolution as 10,000 years ago nobody was able to. The number is still increasing today but at a very slow rate. Therefore, in another 20,000 years the number of lactose tolerant people will have increased. 

Why does lactose intolerance not come out until adulthood? Every baby is born with the ability to digest lactose, except in very rare cases. But as you get older, your lactase levels start to decline as you start producing less of it. This means that there is nothing stopping the lactose from being directly avbsorbed into your colon. Your genetics are also a huge contributor to whether you become lactose intolerant as it is the LCT gene that instructs the body to produce lactase. This gene becomes less affected with age and is dependent on the person for how long it acts efficiently for. This is also reliant on your genetics. This decrease in efficacy can begin to occur once you reach the age of 2 but may not manifest until you are much older. Thus, causing lactose intolerance to appear much later in life.

Therefore, the consumption of dairy products that we so greatly take for granted actually goes against the way our digestive system was built and provides a strong example of how the human body is so well equipped to adapt to its surroundings. This adaptation also shows a strong case study of genetic evolution that enables us to survive and thrive in the conditions we face.