What you carry at this position in your DNA and what research says about it.
Lactose Digestion: 8/10 evidence, 40 publications.
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Sample genotype (not yours): G/G
Lactose Intolerance and Higher LDL
Adults with this genotype typically experience digestive discomfort after consuming dairy products. There is also an association with slightly higher LDL cholesterol levels but a lower average body mass index.
What this genotype means: Lactose intolerance in adulthood; Slightly lower average BMI; Slightly higher LDL cholesterol.
Sample genotype (not yours): A/A
Lactose Tolerant and Lower LDL
Full lactase persistence allows for easy digestion of dairy products throughout life. This genotype is associated with lower LDL cholesterol but a higher average body mass index.
What this genotype means: Full adult lactase persistence; Slightly higher average BMI; Lower average LDL cholesterol.
Sample genotype (not yours): G/A
Lactose Tolerant with Typical LDL
Most individuals with this genotype can comfortably digest dairy products throughout adulthood. This profile is linked to a slightly higher average body mass index but lower LDL cholesterol.
What this genotype means: Lactase persistence and dairy tolerance; Slightly higher average BMI; Slightly lower LDL cholesterol.
Gene function and biological role
Gene Function: The MCM6 gene provides instructions for making a subunit of the minichromosome maintenance complex, which is essential for DNA replication [1]. Beyond its role in cell division, this gene contains a crucial regulatory enhancer region that controls the activity of the neighboring LCT gene [2]. The LCT gene produces lactase, the enzyme responsible for breaking down lactose in milk [3]. Genetic variations within this enhancer region determine whether lactase production continues into adulthood or shuts down after weaning [4].
Variant Impact: This variant, located in an intron of the MCM6 gene, acts as a genetic switch for the nearby lactase gene [2]. The ancestral G allele typically leads to a natural decline in lactase production after infancy [5]. Conversely, the derived A allele creates a binding site for transcription factors that keep the lactase gene active throughout life [3]. This single nucleotide change is the primary driver of adult lactase persistence in populations of European descent [4].
Read on the Lactose Tolerance page
Key Insight: This genetic variant is not actually inside the lactase gene itself, but rather in a neighboring gene where it acts as a remote control switch. The ability to digest milk as an adult evolved so recently in human history that it is considered one of the strongest examples of rapid natural selection.
Location: MCM6. Chromosome 2 · 2q21.3 · 135.9 Mb
Origin Story: Around 5,000 to 10,000 years ago, the rise of dairy farming in Europe created a powerful evolutionary advantage for individuals who could digest milk. Natural selection rapidly increased the frequency of the A allele, transforming a rare mutation into the dominant genetic profile across northern Europe.
Estimated prevalence by population
Global 42.5%; European 13.3%; African 77.2%; East Asian 99.6%; South Asian 70.0%; Americas 59.7%; Ashkenazi 75.6%; Finnish 17.9%; Middle Eastern 88.1%; Amish 5.4%.
Estimated GG genotype frequency.
Global 35.5%; European 46.3%; African 21.3%; East Asian 0.4%; South Asian 27.4%; Americas 35.1%; Ashkenazi 22.7%; Finnish 48.8%; Middle Eastern 11.5%; Amish 35.7%.
Estimated GA genotype frequency.
Global 22.0%; European 40.4%; African 1.5%; East Asian < 0.1%; South Asian 2.7%; Americas 5.2%; Ashkenazi 1.7%; Finnish 33.4%; Middle Eastern 0.4%; Amish 58.9%.
Estimated AA genotype frequency.
Showing effects for G/G genotype
Nutrition & Metabolism
Food Intolerances
Lactose Digestion. Evidence: 8/10. Source: PMID 11788828. Lactose Intolerant.
Dairy Preference. Evidence: 6/10. Source: PMID 35585065. Higher Liking.
Cardiovascular & Metabolic
Obesity & Body Composition
Body Mass Index. Evidence: 10/10. Source: PMID 25673413. Typical BMI.
Lipids & Cholesterol
LDL Cholesterol. Evidence: 9/10. Source: PMID 33619380. Higher LDL.
Organ Systems
Digestive & Gut Disorders
Gut Microbiome. Evidence: 7/10. Source: PMID 32572223. Altered Microbiome.
Showing effects for A/A genotype
Lactose Digestion. Evidence: 8/10. Source: PMID 11788828. Lactose Tolerant.
Dairy Preference. Evidence: 6/10. Source: PMID 35585065. Typical Liking.
Body Mass Index. Evidence: 10/10. Source: PMID 25673413. Higher BMI.
LDL Cholesterol. Evidence: 9/10. Source: PMID 33619380. Typical LDL.
Gut Microbiome. Evidence: 7/10. Source: PMID 32572223. Typical Microbiome.
Showing effects for G/A genotype
Body Mass Index. Evidence: 10/10. Source: PMID 25673413. Slightly Higher BMI.
LDL Cholesterol. Evidence: 9/10. Source: PMID 33619380. Slightly Higher LDL.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Lactase enzyme production naturally declines after early childhood for individuals carrying two copies of the G allele [1]. Consuming milk, cheese, or ice cream often leads to bloating, gas, and abdominal discomfort due to undigested sugars reaching the colon [2]. Interestingly, this digestive profile is associated with a lower overall body mass index, likely due to reduced lifelong dairy intake [3]. However, genetic studies also link this genotype to slightly elevated low-density lipoprotein (LDL) cholesterol levels [4]. The gut microbiome in these individuals often adapts to process alternative carbohydrate sources, showing distinct bacterial ratios compared to dairy consumers [5]. Managing symptoms usually involves choosing lactose-free alternatives or using lactase enzyme supplements [6].
Lactose intolerance in adulthood; Slightly lower average BMI; Slightly higher LDL cholesterol.
Sample genotype: AA (Homozygous)
Maximum adult lactase enzyme activity is maintained by carrying two copies of the A allele [1]. Dairy products can be consumed freely without experiencing the digestive distress of lactose intolerance [2]. This unrestricted diet is linked to a higher average body mass index and body fat percentage over time [3]. However, metabolic profiles show a beneficial association with lower LDL cholesterol levels [4]. Bone mineral density may benefit from the higher calcium intake typically observed in this group [5]. The gut microbiome reflects a stable, dairy-tolerant composition with specific bacterial signatures [6]. Overall, this genotype represents the fully adapted state for pastoralist, dairy-consuming ancestries [7].
Full adult lactase persistence; Slightly higher average BMI; Lower average LDL cholesterol.
Sample genotype: GA (Heterozygous)
Continued production of the lactase enzyme into adulthood is supported by carrying a single copy of the A allele [1]. This genetic setup provides sufficient enzyme activity to prevent the digestive symptoms typically associated with dairy consumption [2]. Lifelong dairy intake in this group is associated with a slightly higher average body mass index compared to those who avoid lactose [3]. Conversely, this metabolic pattern correlates with slightly lower circulating LDL cholesterol levels [4]. The gut microbiome tends to harbor a stable community of bacteria accustomed to dairy-derived nutrients [5]. Calcium absorption is often more efficient due to regular dairy consumption, supporting bone health [6]. Most people with this profile enjoy unrestricted dietary choices regarding dairy [7].
Lactase persistence and dairy tolerance; Slightly higher average BMI; Slightly lower LDL cholesterol.
Variants with shared genetic architecture
rs182549 · MCM6 Gene · Chr 2 · Lactose Tolerance
rs1446585 · R3HDM1 Gene · Chr 2 · Colorectal Cancer Risk
rs10184004 · COBLL1 Gene · Chr 2 · Type 2 Diabetes Risk
Co-regulatory networks of human serum proteins link genetics to disease.
Identification of a variant associated with adult-type hypolactasia.
Mapping the proteo-genomic convergence of human diseases.
Diversity and scale: Genetic architecture of 2068 traits in the VA Million Veteran Program.
Genetic testing for adult-type hypolactasia in Italian families.
Content updated August 2026.
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