Are you a milk drinker? Does pouring a cold glass of milk sound good? Your genes control whether you are likely to produce lactase as an adult, and it is very easy to check your 23andMe or other genetic data to see if you are likely to enjoy a big glass of milk.
Personally, I had always thought it a bit strange when people drink a big glass of milk with dinner. It just didn’t appeal to me…. yuck. I didn’t think ever think about lactose intolerance, though, because I still drink small amounts of milk in my coffee and on cereal. Turns out that I am one of those people who doesn’t produce lactase as an adult. I am relying on bacteria in my gut to break down lactose, so I naturally steer away from drinking a lot of milk at once.
Lactose and Lactase:
Lactose, a sugar in milk, is broken down by lactase, an enzyme produced in the small intestines. This is how babies are able to digest breast milk.
While essential for babies and children to be able to breakdown lactose, for many people, the production of the lactase enzyme stops before adulthood.
Whether or not you still produce lactase as an adult is based on your genes. The persistence of lactase is driven by a genetic variation near the LCT gene.
Thus, many adults are genetically predisposed to not be able to digest larger quantities of milk, also known as lactose intolerance. Others may be able to consume all the dairy that they wish to, with no digestive problems.
Lactose intolerance: Asians vs. European Ancestry
The percentage of the population with genetic variations differs quite a bit among people with different backgrounds.
- Producing lactase as an adult is the most common genotype for European Caucasian populations (90%+ can digest lactose).
- In Asian populations, the vast majority (~99%) do not produce lactase as an adult.
A theory for this occurrence seems to be an adaptation by Caucasian populations in Europe who relied on dairy products as a source of protein. Those who were born with the LCT variant were able to thrive on the higher protein afforded by dairy products. This made it a survival advantage to be able to digest dairy, especially in years when harvests weren’t good.
For people with European Caucasian ancestry, the main variant to look at is rs4988235. It is located in the MCM6 gene, which influences the LCT gene. Approximately 90% of Caucasians will have A/A or A/G and still produce lactase to break down milk as an adult. In Asian populations, less than one percent will carry the G allele.
People with African ancestry may find that they carry a different variant (rs145946881) in the MCM6 gene that also causes lactase persistence as an adult.
Bacteria in the gut can also break down lactose, so even those who don’t produce lactase can often handle digesting limited amounts of milk.
Lactose Intolerance Genotype Report
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Check your genetic data for rs4988235 (23andMe v4, v5; AncestryDNA):
- A/A: Still produces lactase as an adult
- A/G: Still produces lactase as an adult, but less than those with A/A[ref]
- G/G: No longer produces lactase as an adult
Members: Your genotype for rs4988235 is —.
For people of African ancestry, a different variant of the MCM6 gene occurs in about 10-25% of the population and is associated with being able to produce lactase as an adult.
Check your genetic data for rs145946881 (AncestryDNA):
- C/C: Still produces lactase as an adult[ref]
- A/C: Still produces lactase as an adult
- A/A: No longer produces lactase as an adult
Members: Your genotype for rs145946881 is —.
Rare mutations: A very small number of people may also have a rare mutation (not covered by 23andMe or AncestryDNA) that causes the lactase gene not to function at all, even in childhood.
Probiotics to the rescue!
Quite a few studies have looked at the effect of probiotics on lactose intolerance. For example, one study from May 2016 found that a specific strain of Lactobacillus acidophilus was significantly effective in reducing the symptoms of lactose intolerance.
There are many types of lactobacillus bacteria available as probiotics and in yogurt or other fermented dairy foods. It is likely that some strains will be much more effective than others in reducing lactose intolerance symptoms for an individual, and thus, it may be worthwhile to try several different types of Lactobacillus probiotics.
Lactase enzyme supplements:
In many countries, you can buy the lactase enzyme in health food stores and take it along with foods containing dairy. Lactose-free dairy products are also readily available.
Osteoporosis? Maybe not.
Interestingly, a Dutch study showed that while the G/G genotype resulted in adults having a lower dietary calcium intake, it did not correspond to a lower bone density or more fractures.
Recap of your genes:
|Gene||RS ID||Risk Allele||Your Genotype||Notes About Risk Allele|
|LCT||rs4988235||G||--||For GG only: no lactase produced as an adult (lactose intolerant)|
|MCM6||rs145946881||A||--||For AA only: no lactase produced as an adult (African ancestry)|
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Debbie Moon is the founder of Genetic Lifehacks. Fascinated by the connections between genes, diet, and health, her goal is to help you understand how to apply genetics to your diet and lifestyle decisions. Debbie has a BS in engineering and also an MSc in biological sciences from Clemson University. Debbie combines an engineering mindset with a biological systems approach to help you understand how genetic differences impact your optimal health.