Lactose Intolerance

Lactose Intolerance

Lactose is the main carbohydrate in milk and other dairy products. Around 65% of the world's population is lactose intolerant. Lactose intolerance occurs when the body is unable to digest lactose properly. This can result in nausea, abdominal pains and cramps, bloating and diarrhoea - usually occurring a few hours after a person has consumed lactose. The MCM6 gene increases your risk of being lactose intolerant.

What is the MCM6 gene?

The MCM6 gene influences the production of the enzyme lactase. The lactase enzyme is required to break down lactose into glucose and galactose. Only then can it be absorbed into the bloodstream.  

What is the effect of genetic variation at the MCM6 gene?

Genetic variation at the MCM6 gene results in lactose intolerance or lactose tolerance, depending on whether two alleles are present. Historically, there was no genetic variation at the MCM6 gene and lactase was never produced in adulthood, meaning all humans were lactose intolerant. Now, some individuals continue to produce the lactase enzyme into adulthood, allowing them to consume lactose without discomfort.

Individuals who are lactose intolerant do not produce the enzyme lactase during adulthood. Therefore, lactose is unable to be broken down and instead moves through the gut undigested where it is fermented by bacteria. This fermentation is what causes the symptoms associated with lactose intolerance. Nearly 75% of the world is lactose intolerant.

If nearly 75% of the world is lactose intolerant, is lactose not in breast-milk?

Lactose is found in breast milk and almost all newborns are able to digest it (even if they become lactose-intolerant later on in life).

Lactase production is at its peak following birth. At this point in their life, newborns are dependent on milk for their nutrients. Lactase levels are therefore high as it is essential that they are able to break down lactose for their survival. As the child becomes older, the level of lactase production begins to drop and it usually ceases entirely by the age of 9. Despite this, symptoms of lactose intolerance often aren’t detectable immediately.  

Why is lactose intolerance more prevalent in some parts of the world than others?

The prevalence of lactose intolerance varies between different populations of the world. For example, in China 99% of individuals are lactose intolerant, whilst in Northern Europe only 5% of individuals are lactose intolerant.  

The prevalence of lactose tolerance is associated with populations that domesticated cattle. The domestication of cattle occurred nearly 10,000 year ago and in these populations it was beneficial to maintain the ability to digest lactose in milk until adulthood. Hence, the alleles for lactose tolerance were selected for.

Is lactose intolerance an allergy?


Being lactose intolerant is not the same as being allergic to milk or dairy. An allergic reaction occurs when the body reacts to a harmless substance with an immune response. This causes symptoms such as a rash, wheezing and itching. When a person is allergic to something, even a tiny particle can be enough to trigger a reaction.

In comparison, individuals with lactose intolerance can often still consume small amounts of lactose without experiencing any problems.

What can I drink instead of cow’s milk?

Dairy alternatives like soy, oat and almond milk can make great alternatives to cow’s milk. There has been an increase in demand for milk alternatives, so non-dairy options are now widely available in most supermarkets and restaurants. The majority of milk alternatives have added calcium – but do check the label to make sure. Among the milk alternatives, soy milk contains nutrients and vitamins most similar to those found in cow’s milk.

Do probiotics reduce the symptoms of lactose intolerance?

They can do.

Probiotics are live bacteria that are believed to supplement the gastrointestinal flora when consumed. Bifidobacterium animalis is currently the most well-researched and effective strain at reducing lactose intolerance. Supplementation of the probiotic Bifidobacterium animalis have been reported to improve lactose digestion and eliminate symptoms of lactose intolerance by increasing the main groups of colonic microflora.

Other probiotics such as Lactobacillus bulgaricus, Lactobacillus reuteri, and Saccharomyces boulardii show varying degrees of efficacy, many having no effect on the symptoms of lactose intolerance.

Backed by Science

Our in-house scientists have sorted through thousands of studies and we only use genes that are backed by a significant body of peer-reviewed research. Check out Nell’s Science Standard for more information.