Lactose Intolerance: A Story Of Your Genes And Human History

Milk and cheese. No we’re not listing your favorite foods, although some of our tastiest treats do involve these two ingredients. We’re talking about dairy and, more specifically, the inability to consume dairy without some unwanted side effects. Lactose intolerance is somewhat of an enigma, being claimed as a full blown allergy by some and completely ignored by others. While a true intolerance to dairy products may be difficult to pinpoint on symptoms alone, there is actually some genetics involved in our inability to digest dairy products.

So what is it about dairy that makes our tummies grumble? That would be Lactose, the sugar found in any and all milk-based products. When we’re born, our bodies produce an enzyme called Lactase. This enzyme is responsible for breaking down lactose into its two smaller components, galactose and glucose. We produce this enzyme frequently as babies and children so that we’re able to properly digest breast milk, but as we age and wean off of breast milk, our bodies slow the production of the enzyme lactase, meaning that we have a harder time digesting lactose as we get older. This is the reason that so many of us show symptoms of intolerance in late childhood and early adulthood after spending years of consuming dairy without any issues.

Lactose intolerance can vary person to person. In general, symptoms can include bloating, gas, abdominal pain, diarrhea and even nausea. These symptoms normally show themselves anywhere from 30 minutes to two hours after consuming dairy, making it difficult to actually pin down what it was you ate that could be causing so much digestive strife. Eliminating dairy all together for 30 days and then re-introducing it slowly to see how you respond to it is one way to determine intolerance, but an even easier way is to figure it out genetically!

As with most things, there is a gene involved in lactose intolerance and our ability to digest lactose properly. That gene is known as LCT and codes for the production of the lactase enzyme from birth. The issue lies in the gene’s function over time. With age, the LCT gene slows down and codes for less and less of the lactase enzyme. That’s where the MCM6 gene comes into play. Mutations within the MCM6 gene allow for steady performance from the LCT gene, even with age. This means that individuals who carry a specific mutation within the MCM6 gene are actually lactose tolerant and show no symptoms of digestive issues when consuming dairy with age. Mutation at this gene can easily be tested for by extracting DNA from blood or saliva and sequencing it. But this genetic mutation is exciting for reasons other than being able to consume dairy willy nilly with no consequences. It also give science insight into the evolution and history of the human population.

The actual number of people who are lactose intolerant is unknown, but it’s estimated that nearly 65% of the global population exhibits symptoms of intolerance. Interestingly enough, that intolerance varies regionally. Less than 10% of Northern Europeans show any sign if intolerance to dairy while a massive 95% of Asians and Africans exhibit an intolerance in early to late childhood. It’s no surprise that those Europeans who are essentially able to eat lactose without digestive issue carry the MCM6 genetic mutation. In fact, science has traced the mutation back 10,000 to Northwestern Europe, suggesting that the mutation and adaptation occurred alongside the domestication of dairy animals in Europe 12,000 years ago. Because these populations relied to heavily on dairy products as a source of food, their bodies required the enzyme lactase into old age in order to properly digest food. Such domestication of dairy animals wasn’t occurring in Asia and Africa at the same time and so residents there had no need for such a mutation, losing their ability to digest lactose shortly after breast-feeding. Effects of this mutation can still be seen throughout todays population. It’s the reason why most New Zealanders, many of whom descend from Northwestern Europeans, can consume massive amounts of dairy into adulthood without consequence. So, the next time you treat yourself to a milkshake or cheese platter and end up regretting it or don’t notice any digestive symptoms at all, you have both your genes and your ancestors to blame, or maybe even thank.