The Study
A worldwide correlation of lactase persistence phenotype and genotypes
This study looked at where people can digest milk and where they have certain genes, and found that in some places, the genes we know about don't fully explain why people can digest milk. It's like noticing that most kids with red hair have freckles — but not all — so maybe there are other hidden reasons too.
Analysis score
Maximum 85 for a systematic review with meta-analysis.
Where the score came from
Most adults can't digest milk because their bodies stop making the enzyme lactase after babyhood. But in some places, many adults can still drink milk — scientists thought it was just one gene, but now they realize it's more complicated.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 551 / 100
Quality score
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — this means many people in these regions have a different, still-unknown genetic reason for being able to drink milk, which could be important for nutrition and evolution.
- 2Four known gene changes explain milk digestion in Europeans, but not in many African, Middle Eastern, or South Asian populations — even when most people there can digest milk.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
BMC Evolutionary Biology
Year
2010
Authors
Y. Itan, B. L. Jones, Catherine J. E. Ingram, D. Swallow, Mark George Thomas
Related Content
Claims (6)
Most adults worldwide cannot digest lactose after infancy because their bodies stop producing the enzyme lactase, a trait inherited from human ancestors.
In Africa and the Middle East, nearby populations differ in how commonly adults can digest milk, and these differences match their ancestors' historical use of dairy, not shared genetic traits.
In certain populations across Africa, Europe, the Middle East, and Asia, known genetic variants do not fully account for why some people can digest milk as adults, suggesting other genetic variants remain to be discovered.
In populations across western Africa, the Balkans, and parts of South Asia, most people can digest lactose as adults, but this trait is not primarily caused by the four known genetic variants linked to lactase persistence.
Breath hydrogen and blood glucose tests used to identify lactase persistence have unequal rates of false positives and false negatives, and failing to correct for this leads to errors in genetic studies.
There is insufficient genetic and physical trait data from populations in eastern and northern Asia, Indonesia, Melanesia, Australia, and Polynesia to accurately map how lactase persistence evolved in these regions.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.